IgG and kappa free light chain CSF/serum indices: evaluating intrathecal immunoglobulin production in HIV infection in comparison with multiple sclerosis

OBJECTIVES

To study intrathecal kappa free light chain (KFLC) synthesis in people living with HIV (PLWH) in comparison with multiple sclerosis (MS).

METHODS

Cross-sectional analysis including 56 untreated and 150 well treated PLWH, and compared with 58 controls, and 223 MS patients.

RESULTS

Elevated serum/cerebrospinal fluid (CSF) IgG and KFLC indices were observed in untreated PLWH. Seventy percent of untreated PLWH had KFLC index above 6.1, a threshold associated with clinically isolated syndrome/MS diagnosis. No association was found between KFCL index and CSF markers of neuronal injury in either PLWH or MS patients.

CONCLUSIONS

HIV-related immune system dysfunction is often associated with an elevated KFLC index akin to those observed in MS. HIV infection should be considered as a differential diagnosis for patients presenting with neurological symptoms and increased intrathecal immunoglobulin synthesis.

Multiple Sclerosis: From the Application of Oligoclonal Bands to Novel Potential Biomarkers

Multiple sclerosis is a chronic immune-mediated disorder of the central nervous system with a high heterogeneity among patients. In the clinical setting, one of the main challenges is a proper and early diagnosis for the prediction of disease activity. Current diagnosis is based on the integration of clinical, imaging, and laboratory results, with the latter based on the presence of intrathecal IgG oligoclonal bands in the cerebrospinal fluid whose detection via isoelectric focusing followed by immunoblotting represents the gold standard. Intrathecal synthesis can also be evidenced by the measurement of kappa free light chains in the cerebrospinal fluid, which has reached similar diagnostic accuracy compared to that of oligoclonal bands in the identification of patients with multiple sclerosis; moreover, recent studies have also highlighted its value for early disease activity prediction. This strategy has significant advantages as compared to using oligoclonal band detection, even though some issues remain open. Here, we discuss the current methods applied for cerebrospinal fluid analysis to achieve the most accurate diagnosis and for follow-up and prognosis evaluation. In addition, we describe new promising biomarkers, currently under investigation, that could contribute both to a better diagnosis of multiple sclerosis and to its monitoring of the therapeutic treatment response.

Laboratory Diagnosis of Intrathecal Synthesis of Immunoglobulins: A Review about the Contribution of OCBs and K-index

The diagnosis of MS relies on a combination of imaging, clinical examinations, and biological analyses, including blood and cerebrospinal fluid (CSF) assessments. G-Oligoclonal bands (OCBs) are considered a "gold standard" for MS diagnosis due to their high sensitivity and specificity. Recent advancements have involved the introduced of kappa free light chain (k-FLC) assay into cerebrospinal fluid (CSF) and serum (S), along with the albumin quotient, leading to the development of a novel biomarker known as the "K-index" or "k-FLC index". The use of the K-index has been recommended to decrease costs, increase laboratory efficiency, and to skip potential subjective operator-dependent risk that could happen during the identification of OCBs profiles. This review aims to provide a comprehensive overview and analysis of recent scientific articles, focusing on updated methods for MS diagnosis with an emphasis on the utility of the K-index. Numerous studies indicate that the K-index demonstrates high sensitivity and specificity, often comparable to or surpassing the diagnostic accuracy of OCBs evaluation. The integration of the measure of the K-index with OCBs assessment emerges as a more precise method for MS diagnosis. This combined approach not only enhances diagnostic accuracy, but also offers a more efficient and cost-effective alternative.

CD138 as a Specific CSF Biomarker of Multiple Sclerosis

BACKGROUND AND OBJECTIVES

The aim of this study was to identify novel biomarkers for multiple sclerosis (MS) diagnosis and prognosis, addressing the critical need for specific and prognostically valuable markers in the field.

METHODS

We conducted an extensive proteomic investigation, combining analysis of (1) CSF proteome from symptomatic controls, fast and slow converters after clinically isolated syndromes, and patients with relapsing-remitting MS (n = 10 per group) using label-free quantitative proteomics and (2) oligodendrocyte secretome changes under proinflammatory or proapoptotic conditions using stable isotope labeling by amino acids in cell culture. Proteins exhibiting differential abundance in both proteomic analyses were combined with other putative MS biomarkers, yielding a comprehensive list of 87 proteins that underwent quantification through parallel reaction monitoring (PRM) in a novel cohort, comprising symptomatic controls, inflammatory neurologic disease controls, and patients with MS at various disease stages (n = 10 per group). The 11 proteins that passed this qualification step were subjected to a new PRM assay within an expanded cohort comprising 158 patients with either MS at different disease stages or other inflammatory or noninflammatory neurologic disease controls.

RESULTS

This study unveiled a promising biomarker signature for MS, including previously established candidates, such as chitinase 3-like protein 1, chitinase 3-like protein 2, chitotriosidase, immunoglobulin kappa chain region C, neutrophil gelatinase-associated lipocalin, and CD27. In addition, we identified novel markers, namely cat eye syndrome critical region protein 1 (adenosine deaminase 2, a therapeutic target in multiple sclerosis) and syndecan-1, a proteoglycan, also known as plasma cell surface marker CD138 and acting as chitinase 3-like protein 1 receptor implicated in inflammation and cancer signaling. CD138 exhibited good diagnostic accuracy in distinguishing MS from inflammatory neurologic disorders (area under the curve [AUC] = 0.85, CI 0.75-0.95). CD138 immunostaining was also observed in the brains of patients with MS and cultured oligodendrocyte precursor cells but was absent in astrocytes.

DISCUSSION

These findings identify CD138 as a specific CSF biomarker for MS and suggest the selective activation of the chitinase 3-like protein 1/CD138 pathway within the oligodendrocyte lineage in MS. They offer promising prospects for improving MS diagnosis and prognosis by providing much-needed specificity and clinical utility.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that CD138 distinguishes multiple sclerosis from other inflammatory neurologic disorders with an AUC of 0.85 (95% CI 0.75-0.95).

Body fluid markers for multiple sclerosis and differential diagnosis from atypical demyelinating disorders

INTRODUCTION

Body fluid markers could be helpful to predict the conversion into clinically definite multiple sclerosis (MS) in people with a first demyelinating event of the central nervous system (CNS). Consequently, biomarkers such as oligoclonal bands, which are integrated in the current MS diagnostic criteria, could assist early MS diagnosis.

AREAS COVERED

This review examines existing knowledge on a broad spectrum of body fluid markers in people with a first CNS demyelinating event, explores their potential to predict conversion to MS, to assess MS disease activity, as well as their utility to differentiate MS from atypical demyelinating disorders such as neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein associated disease.

EXPERT OPINION

This field of research has shown a dramatic increase of evidence, especially in the last decade. Some biomarkers are already established in clinical routine (e.g. oligoclonal bands) while others are currently implemented (e.g. kappa free light chains) or considered as breakthroughs (e.g. neurofilament light). Determination of biomarkers poses challenges for continuous monitoring, especially if exclusively detectable in cerebrospinal fluid. A handful of biomarkers are measurable in blood which holds a significant potential.

A dynamic interpretation of κFLC index for the diagnosis of multiple sclerosis: a change of perspective

BACKGROUND

Previous studies attempted to define the best threshold for κ free light chains (κFLC) index, confirming higher sensitivity (Se) but less specificity (Sp) compared with IgG oligoclonal bands (OCB) for the diagnosis of MS.

OBJECTIVE

To evaluate the diagnostic accuracy of different κFLC index intervals in a miscellaneous cohort of neurological patients, proposing a procedural flowchart for MS diagnosis.

METHODS

We analyzed data from 607 patients diagnosed with MS (179), CIS (116), other inflammatory (94) or non-inflammatory neurological diseases (218). Measures of diagnostic accuracy were reported for different potential thresholds of κFLC index, and for IgG OCB and IgG index. Binary logistic regression was to used to calculate the odds of being diagnosed with MS based on each increase of κFLC index.

RESULTS

CSF IgG OCB showed 72.2% Se (CI 95% 68.4-75.7) and 95.2% Sp (CI 95% 93.1-96.7) in discriminating between MS/CIS and controls, with an AUC of 0.84 (CI 95% 0.80-0.87). The highest diagnostic accuracy was reported for κFLC index cut-off of 5.0 (Se = 85.4%, Sp = 90.4%, AUC = 0.88), while a threshold of 11.0 exhibited higher Sp (95.5%, 95% CI 93.1-97.1) than IgG OCB. AUCs for all thresholds between 4.25 and 6.6 were not significantly different from each other, but were significantly higher than the AUC of IgG OCB (p < 0.05). The odds of being diagnosed with MS/CIS increased by 17.1% for each unit increase of κFLC index (OR = 1.17; 95% CI 1.12-1.23; p < 0.001).

CONCLUSION

κFLC index performed better than CSF IgG OCB in supporting the diagnosis of MS/CIS, with the advantage of being a cost-effective and quantitative analysis.

Plasma IgG aggregates as biomarkers for multiple sclerosis

We recently reported that multiple sclerosis (MS) plasma contains IgG aggregates and induces complement-dependent neuronal cytotoxicity (Zhou et al., 2023). Using ELISA, we report herein that plasma IgG levels in the aggregates can be used as biomarkers for MS. We enriched the IgG aggregates from samples of two cohorts (190 MS and 160 controls) by collecting flow-through after plasma binding to Protein A followed by detection of IgG subclass. We show that there are significantly higher levels of IgG1, IgG3, and total IgG antibodies in MS IgG aggregates, with an AUC >90%; higher levels of IgG1 distinguish secondary progressive MS from relapsing-remitting MS (AUC = 91%). Significantly, we provided the biological rationale for MS plasma IgG biomarkers by demonstrating the strong correlation between IgG antibodies and IgG aggregate-induced neuronal cytotoxicity. These non-invasive, simple IgG-based blood ELISA assays can be adapted into clinical practice for diagnosing MS and SPMS and monitoring treatment responses.

Establishing the best combination of the kappa free light chain index and oligoclonal bands for an accurate diagnosis of multiple sclerosis

Introduction

The immunoglobulin kappa free light chain (KFLC) index has been proposed as a potentially suitable alternative to oligoclonal IgG bands (OCGB) for diagnosing multiple sclerosis (MS), offering automation and reduced processing time. However, there is no consensus on the preferred approach or how to combine both techniques.

Methods

This prospective cohort study aimed to determine the best utilization of OCGB and KFLC index in patients with a clinically isolated syndrome (CIS) followed for at least two years. OCGB and KFLC were assessed using isoelectric focusing and immunoblotting and turbidimetry, respectively. Sensitivity, specificity, and accuracy for diagnosing MS were calculated for each method.

Results

The study included 371 patients, with 260 (70.1 %) being women, and a median age of 34.9 (27.8 - 43.9) years. Using a cut-off value of 6.1, the KFLC index demonstrated a sensitivity and specificity of 86.3% and 93.9%, respectively. The sensitivity of OCGB (95.3%) was higher (p < 0.001 vs. KFLC index) and the specificity (100%) was comparable to that of the KFLC index (p = 0.5). The concordance between the methods was not uniform across all patients, with 97.8% agreement in patients with KFLC index ≥ 6.1 and 56.0 % in patients with KFLC index < 6.1. In patients with a KFLC index < 6.1, OCGB still identified 75.0 % of MS patients due to its higher sensitivity. An algorithm using the KFLC index as a screening tool and OCGB as an alternative for patients with a negative KFLC index result achieved an accuracy of 96.3 %.

Discussion

Combining the KFLC index and OCGB can provide an easily reproducible and accurate method for diagnosing MS, with OCGB primarily reserved for patients with a KFLC index < 6.1.

Kappa free light chain and neurofilament light independently predict early multiple sclerosis disease activity-a cohort study

BACKGROUND

Inter-individual courses of multiple sclerosis (MS) are extremely variable. The objective of this study was to investigate whether κ-free light chain (κ-FLC) index and serum neurofilament light (sNfL) have an additive predictive value for MS disease activity.

METHODS

Patients with early MS who had cerebrospinal fluid (CSF) and serum sampling at disease onset were followed for four years. At baseline, age, sex, disease duration, number of T2-hyperintense (T2L), and contrast-enhancing T1 lesions (CEL) on MRI were determined. During follow-up, the occurrence of a second clinical attack and start of disease-modifying treatment (DMT) were registered. κ-FLC was measured by nephelometry, and κ-FLC index calculated as [CSF κ-FLC/serum κ-FLC]/albumin quotient. sNfL was determined by single-molecule array, and age- and body-mass-index adjusted Z scores were calculated.

FINDINGS

A total of 86 patients at a mean age of 33 ± 10 years and with a female predominance of 67% were included; 36 (42%) patients experienced a second clinical attack during follow-up. Cox regression analysis adjusted for age, sex, T2L, CEL, disease and follow-up duration, and DMT use during follow-up revealed that both κ-FLC index as well as sNfL Z score independently predict time to second clinical attack. The chance for freedom of relapse within 12 months was 2% in patients with high levels of κ-FLC index (>100) and high sNfL Z score (>3), 30% in patients with high κ-FLC index (>100) and lower sNfL Z score (≤3), 70% in patients with lower κ-FLC index (≤100) but high sNfL Z score (>3), and 90% in patients with lower levels of κ-FLC index (≤100) and sNfL Z score (≤3).

INTERPRETATION

κ-FLC index and sNfL Z score have an additive predictive value for early MS disease activity that is independent of known predictors.

FUNDING

This study was funded by a grant of the charitable foundation of the Austrian Multiple Sclerosis Society.

Determination of sensitivities and specificities of cerebrospinal fluid free light chains to diagnose multiple sclerosis- a multicentric case-control study

BACKGROUND

CSF free light chains help diagnose multiple sclerosis, but no data is available on the Asian population. Our objective was to study the diagnostic utility of CSF free light chains for diagnosing multiple sclerosis in Indian patients.

METHODS

Prospective multicentric case-control study. Cases included those who were tested for oligoclonal bands and fulfilled the modified McDonald criteria 2017 for multiple sclerosis and clinically isolated syndromes. Those tested for oligoclonal bands (OCB) but with other diagnoses- inflammatory and non-inflammatory were included as controls. Clinical details were collected from electronic medical records. CSF and serum kappa and lambda free light chains were measured, apart from oligoclonal bands, immunoglobulin, and albumin in paired serum and CSF samples.

RESULTS

There were 70 patients (31 cases and 39 controls). The mean age was 43.41(SD 16.073) years, and 43(61.4%) were females. CSF kappa showed highest specificity 97.4%, at a cut off 2.06 mg/L (sensitivity 71%) and highest sensitivity 90.3%, at a cut off 0.47 mg/L (specificity 79.5%). Best balance of sensitivity and specificity for CSF kappa was seen at a cut-off of ≥ 0.63 mg/L {sensitivity 87·1 (CI - 70.17-96.37), and specificity 87·18 (CI -72.57-95.70)}. The ratio of Kappa/lambda showed highest specificity of 100%(similar to OCB) with a sensitivity of 71% at a cut off of 1.72. The ratio of sum of kappa and lambda light chains, and Qalb (∑CSF FLC/Qalb), showed the highest specificity (94.87%)among the blood brain barrier corrected ratios.

CONCLUSION

This study showed that the diagnostic utility of CSF kappa was comparable to OCB to diagnose multiple sclerosis in sensitivity, but not specificity, so can be a screening test before testing for OCB in our population.

Cerebrospinal fluid kappa free light chains for the diagnosis of multiple sclerosis: A systematic review and meta-analysis

BACKGROUND

Intrathecal immunoglobulin-G synthesis is a hallmark of multiple sclerosis (MS), which can be detected by oligoclonal IgG bands (OCB) or by κ-free light chains (κ-FLC) in cerebrospinal fluid.

OBJECTIVE

To perform a systematic review and meta-analysis to evaluate whether κ-FLC index has similar diagnostic value to identify patients with clinically isolated syndrome (CIS) or MS compared to OCB, and to determine κ-FLC index cut-off.

METHODS

PubMed was searched for studies that assessed diagnostic sensitivity and specificity of κ-FLC index and OCB to discriminate CIS/MS patients from control subjects. Two reviewers following preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines performed study eligibility assessment and data extraction. Findings from studies were analyzed with bivariate mixed models.

RESULTS

A total of 32 studies were included in the meta-analysis to evaluate diagnostic value of κ-FLC index. Sensitivity and specificity ranged from 52% to 100% (weighted average: 88%) and 69% to 100% (89%) for κ-FLC index and from 37% to 100% (85%) and 74% to 100% (92%) for OCB. Mean difference of sensitivity and specificity between κ-FLC index and OCB was 2 and -4 percentage points. Diagnostic accuracy determined by mixed models revealed no significant difference between κ-FLC index and OCB. A discriminatory cut-off for κ-FLC index was determined at 6.1.

CONCLUSION

The findings indicate that κ-FLC index has similar diagnostic accuracy in MS as OCB.

Cerebrospinal fluid kappa free light chains for the diagnosis of multiple sclerosis: A consensus statement

Cerebrospinal fluid (CSF) analysis is of utmost importance for diagnosis and differential diagnosis of patients with suspected multiple sclerosis (MS). Evidence of intrathecal immunoglobulin G (IgG) synthesis proves the inflammatory nature of the disease, increases diagnostic certainty and substitutes for dissemination in time according to current diagnostic criteria. The gold standard to determine intrathecal IgG synthesis is the detection of CSF-restricted oligoclonal bands (OCBs). However, advances in laboratory methods brought up κ-free light chains (FLCs) as a new biomarker, which are produced in excess over intact immunoglobulins and accumulate in CSF in the case of central nervous system-derived inflammation. Overwhelming evidence showed a high diagnostic accuracy of intrathecal κ-FLC synthesis in MS with sensitivity and specificity of approximately 90% similar to OCB. κ-FLCs have advantages as its detection is fast, easy, cost-effective, reliable, rater-independent and returning quantitative results which might also improve the value of predicting MS disease activity. An international panel of experts in MS and CSF diagnostics developed a consensus of all participants. Six recommendations are given for establishing standard CSF evaluation in patients suspected of having MS. The panel recommended to include intrathecal κ-FLC synthesis in the next revision of MS diagnostic criteria as an additional tool to measure intrathecal immunoglobulin synthesis.

Insight into Early Diagnosis of Multiple Sclerosis by Targeting Prognostic Biomarkers

Multiple sclerosis (MS) is a central nervous system (CNS) immune-mediated disease that mainly strikes young adults and leaves them disabled. MS is an autoimmune illness that causes the immune system to attack the brain and spinal cord. The myelin sheaths, which insulate the nerve fibers, are harmed by our own immune cells, and this interferes with brain signal transmission. Numbness, tingling, mood swings, memory problems, exhaustion, agony, vision problems, and/or paralysis are just a few of the symptoms. Despite technological advancements and significant research efforts in recent years, diagnosing MS can still be difficult. Each patient's MS is distinct due to a heterogeneous and complex pathophysiology with diverse types of disease courses. There is a pressing need to identify markers that will allow for more rapid and accurate diagnosis and prognosis assessments to choose the best course of treatment for each MS patient. The cerebrospinal fluid (CSF) is an excellent source of particular indicators associated with MS pathology. CSF contains molecules that represent pathological processes such as inflammation, cellular damage, and loss of blood-brain barrier integrity. Oligoclonal bands, neurofilaments, MS-specific miRNA, lncRNA, IgG-index, and anti-aquaporin 4 antibodies are all clinically utilised indicators for CSF in MS diagnosis. In recent years, a slew of new possible biomarkers have been presented. In this review, we look at what we know about CSF molecular markers and how they can aid in the diagnosis and differentiation of different MS forms and treatment options, and monitoring and predicting disease progression, therapy response, and consequences during such opportunistic infections.

Kappa Free Light Chain Biomarkers Are Efficient for the Diagnosis of Multiple Sclerosis

Background and Objectives

Kappa free light chains (KFLC) seem to efficiently diagnose MS. However, extensive cohort studies are lacking to establish consensus cut-offs, notably to rule out non-MS autoimmune CNS disorders. Our objectives were to (1) determine diagnostic performances of CSF KFLC, KFLC index, and KFLC intrathecal fraction (IF) threshold values that allow us to separate MS from different CNS disorder control populations and compare them with oligoclonal bands' (OCB) performances and (2) to identify independent factors associated with KFLC quantification in MS.

Methods

We conducted a retrospective multicenter study involving 13 French MS centers. Patients were included if they had a noninfectious and nontumoral CNS disorder, eligible data concerning CSF and serum KFLC, albumin, and OCB. Patients were classified into 4 groups according to their diagnosis: MS, clinically isolated syndrome (CIS), other inflammatory CNS disorders (OIND), and noninflammatory CNS disorder controls (NINDC).

Results

One thousand six hundred twenty-one patients were analyzed (675 MS, 90 CIS, 297 OIND, and 559 NINDC). KFLC index and KFLC IF had similar performances in diagnosing MS from nonselected controls and OIND (p= 0.123 andp= 0.991 for area under the curve [AUC] comparisons) and performed better than CSF KFLC (p< 0.001 for all AUC comparisons). A KFLC index of 8.92 best separated MS/CIS from the entire nonselected control population, with better performances than OCB (p< 0.001 for AUC comparison). A KFLC index of 11.56 best separated MS from OIND, with similar performances than OCB (p= 0.065). In the multivariate analysis model, female gender (p= 0.003), young age (p= 0.013), and evidence of disease activity (p< 0.001) were independent factors associated with high KFLC index values in patients with MS, whereas MS phenotype, immune-modifying treatment use at sampling, and the FLC analyzer type did not influence KFLC index.

Discussion

KFLC biomarkers are efficient tools to separate patients with MS from controls, even when compared with other patients with CNS autoimmune disorder. Given these results, we suggest using KFLC index or KFLC IF as a criterion to diagnose MS.

Classification of Evidence

This study provides Class III evidence that KFLC index or IF can be used to differentiate patients with MS from nonselected controls and from patients with other autoimmune CNS disorders.

Neurodegeneration and humoral response proteins in cerebrospinal fluid associate with pediatric-onset multiple sclerosis and not monophasic demyelinating syndromes in childhood

BACKGROUND

Pediatric-onset multiple sclerosis (POMS) represents the earliest stage of disease pathogenesis. Investigating the cerebrospinal fluid (CSF) proteome in POMS may provide novel insights into early MS processes.

OBJECTIVE

To analyze CSF obtained from children at time of initial central nervous system (CNS) acquired demyelinating syndrome (ADS), to compare CSF proteome of those subsequently ascertained as having POMS versus monophasic acquired demyelinating syndrome (mADS).

METHODS

Patients were selected from two prospective pediatric ADS studies. Liquid chromatography-mass spectrometry (LC-MS) was performed in a Dutch discovery cohort (POMS n = 28; mADS n = 39). Parallel reaction monitoring-mass spectrometry (PRM-MS) was performed on selected proteins more abundant in POMS in a combined Dutch and Canadian validation cohort (POMS n = 48; mADS n = 106).

RESULTS

Discovery identified 5580 peptides belonging to 576 proteins; 58 proteins were differentially abundant with ⩾2 peptides between POMS and mADS, of which 28 more abundant in POMS. Fourteen had increased abundance in POMS with ⩾8 unique peptides. Five selected proteins were all confirmed within validation. Adjusted for age, 2 out of 5 proteins remained more abundant in POMS, that is, Carboxypeptidase E (CPE) and Semaphorin-7A (SEMA7A).

CONCLUSION

This exploratory study identified several CSF proteins associated with POMS and not mADS, potentially reflecting neurodegeneration, compensatory neuroprotection, and humoral response in POMS. The proteins associated with POMS highly correlated with age at CSF sampling.

K index utility as diagnostic and prognostic biomarker in the assessment of patients with suspected Multiple Sclerosis

The aim of the present study is to evaluate the composite role of k index in the initial assessment of Multiple Sclerosis (MS) patients and to select useful cut-offs exportable in clinical practice. We analysed CSF/serum samples of 140 patients and followed-up the CIS/MS subgroup for 7 years. Our results suggest κ index as a quantitative diagnostic and prognostic biomarker in MS, significantly associated to baseline lesion load and to successive clinical course. We propose k index ≥106 as a prognostic cut-off to select patients at major risk of relapse, potentially influencing initial therapeutic decisions.

The Use of Kappa Free Light Chains to Diagnose Multiple Sclerosis

Background: The positive implications of using free light chains in diagnosing multiple sclerosis have increasingly gained considerable interest in medical research and the scientific community. It is often presumed that free light chains, particularly kappa and lambda free light chains, are of practical use and are associated with a higher probability of obtaining positive results compared to oligoclonal bands. The primary purpose of the current paper was to conduct a systematic review to assess the up-to-date methods for diagnosing multiple sclerosis using kappa and lambda free light chains. Method: An organized literature search was performed across four electronic sources, including Google Scholar, Web of Science, Embase, and MEDLINE. The sources analyzed in this systematic review and meta-analysis comprise randomized clinical trials, prospective cohort studies, retrospective studies, controlled clinical trials, and systematic reviews. Results: The review contains 116 reports that includes 1204 participants. The final selection includes a vast array of preexisting literature concerning the study topic: 35 randomized clinical trials, 21 prospective cohort studies, 19 retrospective studies, 22 controlled clinical trials, and 13 systematic reviews. Discussion: The incorporated literature sources provided integral insights into the benefits of free light chain diagnostics for multiple sclerosis. It was also evident that the use of free light chains in the diagnosis of clinically isolated syndrome (CIS) and multiple sclerosis is relatively fast and inexpensive in comparison to other conventional state-of-the-art diagnostic methods, e.g., using oligoclonal bands (OCBs).

Intrathecal B cell-related markers for an optimized biological investigation of multiple sclerosis patients

In multiple sclerosis (MS) disease, the importance of the intrathecal B cell response classically revealed as IgG oligoclonal bands (OCB) in cerebrospinal fluid (CSF) was reaffirmed again in the recently revised diagnostic criteria. We aimed to optimize Laboratory investigation by testing the performance of new B cell-related molecules in CSF (Ig free light chains (FLCκ and λ) and CXCL13 (B-Cell Attracting chemokine1)) for MS diagnosis. 320 paired (CSF-serum) samples were collected from 160 patients with MS (n = 82) and non-MS diseases (n = 78). All patients benefited from IgG index determination, OCB detection, CSF CXCL13 and FLC (κ and λ) measurement in CSF and serum for metrics calculation (κ/λ ratio, FLC-related indexes, and κFLC-intrathecal fraction (IF)). CXCL13 and FLC metrics in CSF were higher in patients with MS and positive OCB. As expected, κFLC metrics—in particular, κFLC index and κFLC IF—had the highest accuracy for MS diagnosis. κ index showed the best performance (sensitivity 83% and specificity 91.7%) at a cut-off of 14.9. Most of the FLC-related parameters were positively correlated with IgG index and the level of CXCL13. In conclusion, the quantitative, standardizable, and technically simple CSF FLCκ metrics seem to be reliable for MS diagnosis, but could not replace OCB detection. CXCL13 appears to be an effective parameter reflecting the intrathecal B cell response. An optimized way for CSF testing combining the conventional and the new B cell-related parameters is proposed in this study.

Evaluation of CSF kappa free light chains for the diagnosis of multiple sclerosis (MS): a comparison with oligoclonal bands (OCB) detection via isoelectric focusing (IEF) coupled with immunoblotting

This study was done to evaluate the diagnostic accuracy of cerebrospinal fluid kappa free light chain (KFLC) for diagnosis of multiple sclerosis, against isoelectrofocusing (IEF) to detect oligoclonal bands (OCB) as gold standard. 64 cases were divided into positive and negative based on the OCB results. Diagnostic accuracy was calculated for the 1 mg/L cut-off. The 1 mg/L cut-off yielded a percent agreement of 86.1% and Cohen's kappa value of 0.8. Youden's index, yielded a cut-off of 0.92 mg/L as optimal (90.3% specificity and 90.9% sensitivity). The analytical time was 3 hours and 55 min for IEF and 25 min for KFLC. The cost of a single OCB test was PKR12 000 (US$68.17) compared with PKR4150 (US$23.58) for KFLC. KFLC proved to be an accurate, cheaper and time-saving alternative and can be performed prior to the contemporary testing.

Evidence for an Intrathecal Immunoglobulin Synthesis by Kappa Free Light Chains in Neurological Patients with an Isolated Band in Isoelectric Focusing

The gold standard for detecting intrathecal immunoglobulin synthesis is the determination of the oligoclonal band (OCB) in the cerebrospinal fluid (CSF) using isoelectric focusing (IEF). Controversy still exists regarding the significance of an isolated band in the CSF. A highly promising alternative method for the assessment of intrathecal inflammation is the quantification of kappa free light chains (k-FLC). Our aim was to evaluate the clinical significance of quantitative k-FLC in patients with an isolated band in the CSF. Using the Human Kappa Freelite Mx Kit on a turbidimetric Optilite®, we quantified the k-FLCs in paired CSF and serum samples in 47 patients with a single band in IEF. We classified patients into 27× inflammatory neurological disorders (IND), 2× peripheral inflammatory neurological disorders (PIND), 9× non-inflammatory neurological disorders (NIND) and 9× symptomatic controls (SC) based on their medical diagnosis. k-FLC were below the lower measurement limit of the analyser (LML) in all SC and PIND, as well as in 8 out of 9 NIND and 11 IND. Only 1 NIND and 16 IND were above the LML, and of these, only 14 IND were above the upper discrimination limit (Qlim). A neuroinflammatory nature of the diseases can be indicated in many cases by positive k-FLC in patients with an isolated band in IEF. The measurement of k-FLC can support the diagnosis of neurological diseases if they are included in the routine work-up.

A Scoping Review on Body Fluid Biomarkers for Prognosis and Disease Activity in Patients with Multiple Sclerosis

Multiple sclerosis (MS) is a complex demyelinating disease of the central nervous system, presenting with different clinical forms, including clinically isolated syndrome (CIS), which is a first clinical episode suggestive of demyelination. Several molecules have been proposed as prognostic biomarkers in MS. We aimed to perform a scoping review of the potential use of prognostic biomarkers in MS clinical practice. We searched MEDLINE up to 25 November 2021 for review articles assessing body fluid biomarkers for prognostic purposes, including any type of biomarkers, cell types and tissues. Original articles were obtained to confirm and detail the data reported by the review authors. We evaluated the reliability of the biomarkers based on the sample size used by various studies. Fifty-two review articles were included. We identified 110 molecules proposed as prognostic biomarkers. Only six studies had an adequate sample size to explore the risk of conversion from CIS to MS. These confirm the role of oligoclonal bands, immunoglobulin free light chain and chitinase CHI3L1 in CSF and of serum vitamin D in the prediction of conversion from CIS to clinically definite MS. Other prognostic markers are not yet explored in adequately powered samples. Serum and CSF levels of neurofilaments represent a promising biomarker.

The kappa free light chain index and oligoclonal bands have a similar role in the McDonald criteria

Intrathecal production of kappa free light chains (KFLC) occurs in multiple sclerosis and can be measured using the KFLC index. KFLC index values can be determined more easily than oligoclonal bands (OB) detection and seem more sensitive than the immunoglobulin (Ig)G index to diagnose multiple sclerosis. We assessed the value of OB, KFLC index cut-offs 5.9, 6.6, and 10.61, and IgG index to diagnose multiple sclerosis with prospectively acquired data from a clinically isolated syndrome (CIS) inception cohort. We selected patients with sufficient data to determine OB positivity, MRI dissemination in space (DIS) and time (DIT), IgG index, and sufficient quantities of paired CSF and blood samples to determine KFLC indexes (n = 214). We used Kendall´s Tau coefficient to estimate concordance; calculated the number of additional diagnoses when adding each positive index to DIS and positive OB; performed survival analyses for OB and each index with the outcomes second attack and 2017 MRI DIS and DIT; and estimated the diagnostic properties of OB and the different indexes for the abovementioned outcomes at five years. OB were positive in 138 patients (64.5%), KFLC-5.9 in 136 (63.6%), KFLC-6.6 in 135 (63.1%), KFLC-10.61 in 126 (58.9%) and IgG index in 101 (47.2%). The highest concordance was between OB and KFLC-6.6 (τ=0.727) followed by OB and KFLC-5.9 (τ=0.716). Combining DIS plus OB or KFLC-5.9 increased the number of diagnosed patients by 11 (5.1%), with KFLC-6.6 by 10 (4.7%), with KFLC-10.61 by 9 (4.2%), and with IgG index by 3 (1.4%). Patients with positive OB or indexes reached second attack and MRI DIS and DIT faster than patients with negative results (P < 0.0001 except IgG index in second attack: P = 0.016). In multivariable Cox models [aHR (95% CI)], the risk for second attack was very similar between KFLC-5.9 [2.0 (0.9-4.3), P = 0.068] and KFLC-6.6 [2.1 (1.1-4.2), P = 0.035]. The highest risk for MRI DIS and DIT was demonstrated with KFLC-5.9 [4.9 (2.5-9.6), P < 0.0001], followed by KFLC-6.6 [3.4 (1.9-6.3), P < 0.0001]. KFLC-5.9 and KFLC-6.6 had a slightly higher diagnostic accuracy than OB for second attack (70.5, 71.1, and 67.8) and MRI DIS and DIT (85.7, 85.1, and 81.0). KFLC indexes 5.9 and 6.6 performed slightly better than OB to assess multiple sclerosis risk and in terms of diagnostic accuracy. Given the concordance between OB and these indexes, we suggest using DIS plus positive OB or positive KFLC index as a modified criterion to diagnose multiple sclerosis.

Mono/polyclonal free light chains as challenging biomarkers for immunological abnormalities

Free light chain (FLC) kappa (k) and lambda (λ) consist of low molecular weight proteins produced in excess during immunoglobulin synthesis and secreted into the circulation. In patients with normal renal function, over 99% of FLCs are filtered and reabsorbed. Thus, the presence of FLCs in the serum is directly related to plasma cell activity and the balance between production and renal clearance. FLCs are bioactive molecules that may exist as monoclonal (m) and polyclonal (p) FLCs. These have been detected in several body fluids and may be key indicators of ongoing damage and/or illness. International guidelines now recommend mFLC for screening, diagnosis and monitoring multiple myeloma and other plasma cell dyscrasias. In current clinical practice, FLCs in urine indicate cast nephropathy and other renal injury, whereas their presence in cerebrospinal fluid is important for identifying central nervous system inflammatory diseases such as multiple sclerosis. Increased pFLCs have also been detected in various conditions characterized by B cell activation, i.e., chronic inflammation, autoimmune disease and HCV infection. Monitoring the coronavirus (COVID-19) pandemic by analysis of salivary FLCs presents a significant opportunity in clinical immunology worthy of scientific pursuit.

Inter-Laboratory Concordance of Cerebrospinal Fluid and Serum Kappa Free Light Chain Measurements

The kappa index (K-Index), calculated by dividing the cerebrospinal fluid (CSF)/serum kappa free light chain (KFLC) ratio by the CSF/serum albumin ratio, is gaining increasing interest as a marker of intrathecal immunoglobulin synthesis. However, data on inter-laboratory agreement of these measures is lacking. The aim was to assess the concordance of CSF and serum KFLC measurements, and of K-index values, across different laboratories. KFLC and albumin of 15 paired CSF and serum samples were analyzed by eight participating laboratories. Four centers used Binding Site instruments and assays (B), three used Siemens instruments and assays (S), and one center used a Siemens instrument with a Binding Site assay (mixed). Absolute individual agreement was calculated using a two-way mixed effects intraclass correlation coefficient (ICC). Cohen's kappa coefficient (k) was used to measure agreement on positive (≥5.8) K-index values. There was an excellent agreement in CSF KFLC measurements across all laboratories (ICC (95% confidence interval): 0.93 (0.87-0.97)) and of serum KFLC across B and S laboratories (ICC: 0.91 (0.73-0.97)), while ICC decreased (to 0.81 (0.53-0.93)) when including the mixed laboratory in the analysis. Concordance for a positive K-Index was substantial across all laboratories (k = 0.77) and within S laboratories (k = 0.71), and very good (k = 0.89) within B laboratories, meaning that patients rarely get discordant results on K-index positivity notwithstanding the testing in different laboratories and the use of different platforms/assays.

Molecular Biomarkers and Their Implications for the Early Diagnosis of Selected Neurodegenerative Diseases

The degeneration and dysfunction of neurons are key features of neurodegenerative diseases (NDs). Currently, one of the main challenges facing researchers and clinicians is the ability to obtain reliable diagnostic tools that will allow for the diagnosis of NDs as early as possible and the detection of neuronal dysfunction, preferably in the presymptomatic stage. Additionally, better tools for assessing disease progression in this group of disorders are also being sought. The ideal biomarker must have high sensitivity and specificity, be easy to measure, give reproducible results, and reflect the disease progression. Molecular biomarkers include miRNAs and extracellular microvesicles known as exosomes. They may be measured in two extracellular fluids of the highest importance in NDs, i.e., cerebrospinal fluid (CSF) and blood. The aim of the current review is to summarize the pathophysiology of the four most frequent NDs—i.e., Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS)—as well as current progress in the research into miRNAs as biomarkers in these major neurodegenerative diseases. In addition, we discuss the possibility of using miRNA-based therapies in the treatment of neurodegenerative diseases, and present the limitations of this type of therapy.

Kappa Free Light Chains in Cerebrospinal Fluid in Inflammatory and Non-Inflammatory Neurological Diseases

Background: Oligoclonal bands represent intrathecal immunoglobulin G (IgG) synthesis and play an important role in the diagnosis of multiple sclerosis (MS). Kappa free light chains (KFLC) are increasingly recognized as an additional biomarker for intrathecal Ig synthesis. However, there are limited data on KFLC in neurological diseases other than MS. Methods: This study, conducted at two centers, retrospectively enrolled 346 non-MS patients. A total of 182 patients were diagnosed with non-inflammatory and 84 with inflammatory neurological diseases other than MS. A further 80 patients were classified as symptomatic controls. Intrathecal KFLC production was determined using different approaches: KFLC index, Reiber’s diagram, Presslauer’s exponential curve, and Senel’s linear curve. Results: Matching results of oligoclonal bands and KFLC (Reiber’s diagram) were frequently observed (93%). The Reiber’s diagram for KFLC detected intrathecal KFLC synthesis in an additional 7% of the patient samples investigated (4% non-inflammatory; 3% inflammatory), which was not found by oligoclonal band detection. Conclusions: The determination of both biomarkers (KFLC and oligoclonal bands) is recommended for routine diagnosis and differentiation of non-inflammatory and inflammatory neurological diseases. Due to the high sensitivity and physiological considerations, the assessment of KFLC in the Reiber’s diagram should be preferred to other evaluation methods.

CSF Kappa Free Light Chains: Cutoff Validation for Diagnosing Multiple Sclerosis

OBJECTIVE

To determine and validate a cerebrospinal fluid (CSF) κ (KCSF) value statistically comparable to detection of CSF-specific oligoclonal bands (OCB) to support the diagnosis of multiple sclerosis (MS).

PATIENTS AND METHODS

A total of 702 retrospective and 657 prospective paired CSF/serum samples from residual waste samples of physician-ordered OCB tests were obtained and tested for KCSF at Mayo Clinic. Charts were reviewed by a neurologist blinded to KCSF results. Specificity and sensitivity for MS diagnosis were evaluated to establish a diagnostic cutoff value for KCSF in the retrospective cohort and then validated in the prospective cohort.

RESULTS

Retrospective and prospective subgroups, respectively, included MS (n=85, 70), non-MS (n=615, 585), and undetermined diagnosis (excluded, n=2, 2). The retrospective data established a KCSF cutoff value of 0.1 mg/dL to be comparable to OCB testing. In the retrospective subgroup, KCSF vs OCB sensitivities for diagnosis of MS were 68.2% vs 75.0% (P=.08) and specificities were 86.1% vs 87.6% (P=.27). The KCSF area under the receiver operating characteristic curve was 0.772 (95% CI, 0.720 to 0.824), and for OCB was 0.813 (95% CI, 0.764 to 0.861). The prospective cohort was then used to validate the diagnostic KCSF value of 0.1 mg/dL; KCSF vs OCB sensitivities were 78.6% for both (P>.99) and specificities were 87.1% vs 89.4% (P=.09).

CONCLUSION

The KCSF value of 0.1 mg/dL is a valid alternative to OCB testing, offering a standardized quantitative measure, eliminating human error, reducing cost and turnaround time, with no significant difference in sensitivity and specificity. This study provides class I evidence that a KCSF value of 0.1 mg/dL can be used in place of OCB testing to support the diagnosis of MS.

Cerebrospinal fluid kappa free light chains as biomarker in multiple sclerosis—from diagnosis to prediction of disease activity

Multiple sclerosis (MS) is a chronic immune-mediated disorder of the central nervous system that shows a high interindividual heterogeneity, which frequently poses challenges regarding diagnosis and prediction of disease activity. In this context, evidence of intrathecal inflammation provides an important information and might be captured by kappa free light chains (κ-FLC) in the cerebrospinal fluid (CSF). In this review, we provide an overview on what is currently known about κ‑FLC, its historical development, the available assays and current evidence on its diagnostic and prognostic value in MS. Briefly, intrathecal κ‑FLC synthesis reaches similar diagnostic accuracy compared to the well-established CSF-restricted oligoclonal bands (OCB) to identify patients with MS, and recent studies even depict its value for prediction of early MS disease activity. Furthermore, detection of κ‑FLC has significant methodological advantages in comparison to OCB detection.

The Influence of Renal Function Impairment on Kappa Free Light Chains in Cerebrospinal Fluid

Background

The determination of kappa free light chains (KFLC) in cerebrospinal fluid (CSF) is an upcoming biomarker for the detection of an intrathecal immunoglobulin synthesis. Since renal function impairment leads to altered serum KFLC and albumin concentrations, interpretation of KFLC in CSF may be influenced by these parameters.

Methods

In this two-center study, the influence of renal function (according to the CKD-EPI creatinine equation) on KFLC and albumin concentrations was investigated in patients with "physiological" (n = 139), "non-inflammatory" (n = 146), and "inflammatory" (n = 172) CSF profiles in respect to the KFLC index and the evaluation in quotient diagrams in reference to the hyperbolic reference range (KFLC IF).

Results

All sample groups displayed declining KFLC indices and KFLC IF values with decreasing renal function (P-values between <.0001 and .0209). In "inflammatory" CSF profile samples, 15% of the patients presented a KFLC index <5.9 while 10% showed an intrathecal KFLC fraction below Q_Kappa(lim), suggesting possible false negative KFLC results.

Conclusions

The influence of renal function should be considered while interpreting KFLC results in patients with neuroinflammatory diseases. The interpretation of KFLC in quotient diagrams is less susceptible to renal function impairment than the KFLC index and should be preferentially used.

The Increasing Role of Kappa Free Light Chains in the Diagnosis of Multiple Sclerosis

Free light chains (FLC) are a promising biomarker to detect intrathecal inflammation in patients with inflammatory central nervous system (CNS) diseases, including multiple sclerosis (MS). The diagnostic use of this biomarker, in particular the kappa isoform of FLC ("KFLC"), has been investigated for more than 40 years. Based on an extensive literature review, we found that an agreement on the correct method for evaluating KFLC concentrations has not yet been reached. KFLC indices with varying cut-off values and blood-CSF-barrier (QAlbumin) related non-linear formulas for KFLC interpretation have been investigated in several studies. All approaches revealed high diagnostic sensitivity and specificity compared with the oligoclonal bands, which are considered the gold standard for the detection of intrathecally synthesized immunoglobulins. Measurement of KFLC is fully automated, rater-independent, and has been shown to be stable against most pre-analytic influencing factors. In conclusion, the determination of KFLC represents a promising diagnostic approach to show intrathecal inflammation in neuroinflammatory diseases. Multicenter studies are needed to show the diagnostic sensitivity and specificity of KFLC in MS by using the latest McDonald criteria and appropriate, as well as standardized, cut-off values for KFLC concentrations, preferably considering non-linear formulas such as Reiber's diagram.

Evaluation of Kappa Index as a Tool in the Diagnosis of Multiple Sclerosis: Implementation in Routine Screening Procedure

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. Previous studies have shown that cerebrospinal fluid (CSF) kappa free light chains (K-FLCs) may have a role in MS diagnosis. In this regard, the kappa index (K-Index) has demonstrated higher sensitivity, and slightly lower specificity than oligoclonal bands (OCBs), the gold standard for the detection of intrathecal immunoglobulin synthesis, a feature of MS. Here, we evaluated the performance of the K-Index (K-Index = CSF/serum K-FLC divided by CSF/serum albumin) for the differential diagnosis of MS in a cohort of patients with suspected MS. K-FLCs were quantitatively measured in parallel serum and CSF samples by turbidimetry (Freelite Mx reagent on an Optilite system, The Binding Site Group Ltd). From 160 (63.4%) of a total of 252 patients who had K-FLC in CSF <0.03 mg/dl, below the sensitivity limit of the technique, only one had a diagnosis of MS. However, the absence of OCB in this same patient suggested no synthesis of intrathecal immunoglobulin. Globally, MS patients presented significantly higher K-Index levels than patients without an MS diagnosis (66.96 vs. 0.025, respectively; p < 0.0001). In agreement, patients with positive OCB testing also exhibited higher K-Index levels than patients negative for OCB (65.02 vs. 0.024, respectively; p < 0.0001). An optimal K-Index cutoff of 3.045 was defined by receiver operating characteristic (ROC) analysis for screening suspected MS, achieving a higher diagnostic sensitivity and slightly lower specificity than OCB (Sens. 0.9778 and Spec. 0.8629 vs. Sens. 0.8889 and Spec. 0.9086, respectively). A previously reported K-Index cutoff of 6.6 also showed good diagnostic performance (Sens. 0.9333; Spec. 0.8731), validating its power as a diagnostic biomarker for MS. Finally, a time- and cost-effective algorithm for MS screening is proposed that would offer an initial rapid evaluation of the intrathecal immunoglobulin synthesis through the K-FLC in CSF and K-Index analysis, followed by reflexing OCB testing that may be ordered more selectively.

[Herpesviruses and biomarkers in disseminated encephalomyelitis and multiple sclerosis in children (part II)]

Recently, the problem of demyelinating diseases in children is still very acute. This occurs, on the one hand, by high access and specificity of diagnostic methods and, on the other hand - by high morbidity of children different neuroinfectious diseases which can lead to demyelinating diseases. This literature review presents the currently available information on the autoantibodies and neurospecific protein role in the development of multiple sclerosis and acute disseminative encephalitis in children. The authors also describe their experience of complex etiopatogenic therapy and cytoflavin use that helps to reduce frequency and expression of demyelinating process and endothelium dysfunction in case of active herpesvirus infection.

Kappa-Free Light Chains in CSF Predict Early Multiple Sclerosis Disease Activity

Objective

To investigate whether κ-free light chain (κ-FLC) index predicts multiple sclerosis (MS) disease activity independent of demographics, clinical characteristics, and MRI findings.

Methods

Patients with early MS who had CSF and serum sampling at disease onset were followed for 4 years. At baseline, age, sex, type of symptoms, corticosteroid treatment, and number of T2 hyperintense (T2L) and contrast-enhancing T1 lesions (CELs) on MRI were determined. During follow-up, the occurrence of a second clinical attack and start of disease-modifying therapy (DMT) were registered. κ-FLCs were measured by nephelometry, and κ-FLC index calculated as [CSF κ-FLC/serum κ-FLC]/albumin quotient.

Results

A total of 88 patients at a mean age of 33 ± 10 years and female predominance of 68% were included; 38 (43%) patients experienced a second clinical attack during follow-up. In multivariate Cox regression analysis adjusting for age, sex, T2L, CEL, disease and follow-up duration, administration of corticosteroids at baseline and DMT during follow-up revealed that κ-FLC index predicts time to second clinical attack. Patients with κ-FLC index >100 (median value 147) at baseline had a twice as high probability for a second clinical attack within 12 months than patients with low κ-FLC index (median 28); within 24 months, the chance in patients with high κ-FLC index was 4 times as high as in patients with low κ-FLC index. The median time to second attack was 11 months in patients with high κ-FLC index whereas 36 months in those with low κ-FLC index.

Conclusion

High κ-FLC index predicts early MS disease activity.

Classification of Evidence

This study provides Class II evidence that in patients with early MS, high κ-FLC index is an independent risk factor for early second clinical attack.

[Herpesviruses and biomarkers in disseminated encephalomyelitis and multiple sclerosis in children]

The relevance of the study of demyelinating diseases is due to their increasing frequency in children, clarification of the role of infectious agents in their genesis, as well as the possibility of transformation of disseminated encephalomyelitis into multiple sclerosis. The literature review presents the currently available information on the causes of the development of demyelinating diseases, biomarkers of disseminated encephalomyelitis and multiple sclerosis, the causes of an unfavorable course and possible laboratory parameters indicating the transition from one disease to another, which can be used as prognostic factors. The authors also noted the experience of the authors on the importance of adequate etiopathogenetic therapy in changing the nature of the course of the disease, in particular, when confirming the relationship between the frequency of exacerbations of ADEM and MS with the activation of herpesvirus infections, courses of specific antiviral therapy are effective, as well as pathogenetic therapy aimed at correcting endothelial dysfunction using the drug cytoflavin.

Evidence of Oligoclonal Bands Does Not Exclude Non-Inflammatory Neurological Diseases

Cerebrospinal fluid analysis is an essential part of the diagnostic workup in various neurological disorders. Evidence of an intrathecal immunoglobulin synthesis, as demonstrated by Reiber’s diagram or the more sensitive oligoclonal bands (OCB), are typical for neuroinflammatory diseases, and normally not expected in non-inflammatory neurological diseases. Therefore, patients with non-inflammatory neurological diseases are often used in control groups in studies investigating autoimmune diseases of the central nervous system. However, data about the frequency of intrathecal immunoglobulin synthesis in non-inflammatory neurological disease are scarce. The cerebrospinal fluid (CSF) records of a total of 3622 patients were screened and 2114 patients included with presumably non-inflammatory neurological diseases like dementia, idiopathic peripheral neuropathy, motoneuron disease, stroke, and epileptic seizures. Evidence of an intrathecal immunoglobulin synthesis can be found with low frequency also in non-inflammatory neurological diseases. A much higher rate of patients showed intrathecal immunoglobulin synthesis as demonstrated by OCB than by Reiber’s diagram. In patients with disorders of the peripheral nervous system the frequency of OCB was much lower than in patients presenting with central nervous system manifestations. Evidence of an intrathecal immunoglobulin synthesis should not automatically lead to exclusion of non-inflammatory neurological diseases but should rather prompt the way to investigate for the origin of the intrathecal immunoglobulin synthesis.

Intrathecal kappa free light chains as markers for multiple sclerosis

Cerebrospinal fluid (CSF) kappa free light chain (KFLC) index has been described as a reliable marker of intrathecal IgG synthesis to diagnose multiple sclerosis (MS). Our aims were: (1) to compare the efficiency of KFLC through different interpretation approaches in diagnosing MS. (2) to evaluate the prognostic value of KFLC in radiologically and clinically isolated syndromes (RIS-CIS). We enrolled 133 MS patients and 240 with other neurological diseases (93 inflammatory including 18 RIS-CIS, 147 non-inflammatory). Albumin, lambda free light chain (LFLC) and KFLC were measured in the CSF and serum by nephelometry. We included two groups of markers: (a) corrected for blood-CSF barrier permeability: immunoglobulin G (IgG), KFLC and LFLC indexes. (b) CSF ratios (not including albumin and serum-correction): CSF KFLC/LFLC, CSF KFLC/IgG, CSF LFLC/IgG. KFLC were significantly higher in MS patients compared to those with other diseases (both inflammatory or not). KFLC index and CSF KFLC/IgG ratio showed high sensitivity (93% and 86.5%) and moderate specificity (85% and 88%) in diagnosing MS. RIS-CIS patients who converted to MS showed greater KFLC index and CSF KFLC/IgG. Despite OB are confirmed to be the gold-standard to detect intrathecal IgG synthesis, the KFLC confirmed their accuracy in MS diagnosis. A “kappa-oriented” response characterizes MS and has a prognostic impact in the RIS-CIS population.

Free light chains in the cerebrospinal fluid. Comparison of different methods to determine intrathecal synthesis

Background Free light chains (FLC) have been proposed as diagnostic biomarkers in the cerebrospinal fluid (CSF) of patients with inflammatory central nervous system (CNS) diseases. However, which method to use for determining an intrathecal FLC synthesis has not yet been clarified. The objective of this study was to compare the diagnostic performance of CSF FLC concentration, FLC quotient (QFLC), FLC index and FLC intrathecal fraction (FLCIF). Methods κ- and λ-FLC were measured by nephelometry under blinded conditions in CSF and serum sample pairs of patients with clinically isolated syndrome (CIS; n = 60), multiple sclerosis (MS; n = 60) and other neurological diseases (n = 60) from four different MS centers. QFLC was calculated as the ratio of CSF/serum FLC concentration, the FLC index as QFLC/albumin quotient and the percentage FLCIF by comparing QFLC to a previously empirically determined, albumin quotient-dependent reference limit. Results CSF FLC concentration, QFLC, FLC index and FLCIF of both the κ- and λ-isotype were significantly higher in patients with CIS and MS than in the control group, as well as in oligoclonal bands (OCB) positive than in OCB negative patients. Each parameter was able to identify MS/CIS patients and OCB positivity, however, diagnostic performance determined by receiver operating characteristic (ROC) analyses differed and revealed superiority of FLC index and FLCIF. Conclusions These findings support the diagnostic value of FLC measures that correct for serum FLC levels and albumin quotient, i.e. blood-CSF barrier function.

Prognostic value of kappa free light chains determination in first-ever multiple sclerosis relapse

Given its highly variable clinical course, an unmet need for objective prognostic assessment in Multiple Sclerosis (MS) persists. In this work, we suggest that CSF kappa free light chains (KFLC) determination at first relapse may provide insight into future disease activity and disability worsening. We quantified KFLC by nephelometry in paired CSF/serum samples of 28 patients, collected within one month of first-ever MS relapse, and explored correlations with clinical data on disease activity, retrospectively registered across a median follow-up time of 79 months. We documented KFLC ratio (CSF-FKLC/Serum-KFLC) as an independent predictor of second relapse occurrence and disability worsening at follow-up, in this cohort.

Cerebrospinal Fluid Testing for Multiple Sclerosis

Multiple sclerosis is one of the most common autoimmune diseases affecting the central nervous system. Current guidelines characterize multiple sclerosis and related conditions based on clinical, imaging, and body fluid markers. In this review, we describe how laboratory analysis of cerebrospinal fluid is currently performed and discuss new approaches under development for multiple sclerosis diagnostics.

Kappa free light chains is a valid tool in the diagnostics of MS: A large multicenter study

OBJECTIVE

To validate kappa free light chain (KFLC) and lambda free light chain (LFLC) indices as a diagnostic biomarker in multiple sclerosis (MS).

METHODS

We performed a multicenter study including 745 patients from 18 centers (219 controls and 526 clinically isolated syndrome (CIS)/MS patients) with a known oligoclonal IgG band (OCB) status. KFLC and LFLC were measured in paired cerebrospinal fluid (CSF) and serum samples. Gaussian mixture modeling was used to define a cut-off for KFLC and LFLC indexes.

RESULTS

The cut-off for the KFLC index was 6.6 (95% confidence interval (CI) = 5.2-138.1). The cut-off for the LFLC index was 6.9 (95% CI = 4.5-22.2). For CIS/MS patients, sensitivity of the KFLC index (0.88; 95% CI = 0.85-0.90) was higher than OCB (0.82; 95%CI = 0.79-0.85; p < 0.001), but specificity (0.83; 95% CI = 0.78-0.88) was lower (OCB = 0.92; 95% CI = 0.89-0.96; p < 0.001). Both sensitivity and specificity for the LFLC index were lower than OCB.

CONCLUSION

Compared with OCB, the KFLC index is more sensitive but less specific for diagnosing CIS/MS. Lacking an elevated KFLC index is more powerful for excluding MS compared with OCB but the latter is more important for ruling in a diagnosis of CIS/MS.

Diagnostic accuracy of intrathecal kappa free light chains compared with OCBs in MS

OBJECTIVE

To determine what kappa free light chain (KFLC) metric has the highest capacity to separate healthy patients from patients with MS, we evaluated the sensitivity, specificity, and the overall diagnostic accuracy of 4 different KFLC metrics. To assess the usefulness of KFLC in the diagnostics of MS, we compared the different KFLC metrics with oligoclonal bands (OCBs), the current gold standard biochemical method to demonstrate intrathecal antibody production.

METHODS

CSF and plasma were collected from patients with confirmed or suspected MS, other neurological diseases, as well as symptomatic and healthy controls between May 2017 and May 2018 (n = 335) at the Department of Neurology, Karolinska University Hospital, as part of routine diagnostic workup. KFLC analysis and isoelectric focusing for the detection of oligoclonal bands (OCB) were determined and correlated with diagnosis. Receiver operating characteristic (ROC) curve analysis was used to determine accuracy.

RESULTS

OCBs yielded a sensitivity of 87% and a specificity of 100%. All KFLC metrics showed a high sensitivity (89%-95%) and specificity (95%-100%). Using the optimal cutoff according to the Youden Index resulted for the KFLC intrathecal fraction in a cutoff of -0.41 with a sensitivity of 95% and a specificity of 97% and for CSF KFLC/CSF albumin with a cutoff of 1.93 × 10^-3 with a sensitivity of 94% and specificity of 100%.

CONCLUSION

All evaluated KFLC metrics have excellent accuracy, and both KFLC intrathecal fraction and CSF KFLC/CSF albumin are at least as good as OCB in separating patients with MS from a control group.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that CSF KFLC accurately distinguishes patients with MS from healthy controls.

Free light chain kappa and the polyspecific immune response in MS and CIS - Application of the hyperbolic reference range for most reliable data interpretation

OBJECTIVES

Free light chain kappa (FLC-k) in cerebrospinal fluid (CSF) is involved in intrathecal immune responses and is being investigated frequently for its diagnostic sensitivity. The objective of this study was the application and interpretation of FLC-k data in quotient diagrams with a hyperbolic reference range and to confirm the superior evaluation in comparison with another proposed reference method and cut-off values. Secondly, the performance of the FLC-k quotient diagram was analyzed in respect to MS and CIS patients and in relation to the polyspecific immune response.

MATERIALS AND METHODS

FLC-k was analyzed in a control cohort (n = 302) and in patients with MS/CIS (n = 98) using a nephelometric FLC-k kit. The intrathecal fraction of FLC-k based on the hyperbolic reference range was calculated in comparison to various linear FLC-k indices and routine CSF parameters [oligoclonal bands (OCB), polyspecific antiviral immune response].

RESULTS

Using the new hyperbolic reference range, intrathecal FLC-k synthesis was found in 20 / 302 OCB negative controls. The sensitivity in the definitive MS cohort was 100%, compared to 93% positive OCB. The linear FLC-k Index interpretation with similar sensitivity for MS, however, bares the risk for the control samples,depending on the reference range, of false positive interpretations (up to 7 at low QAlb) or false negative interpretations (up to 17/20 FLC-k positives at high QAlb). The quantitative mean intrathecal FLC-k synthesis in the CIS cohort (later MS) was even slightly higher than in initially definitive MS questioning a pathophysiological difference. A positive MRZ reaction found in 53% percent of CIS patients with intrathecal FLC-k synthesis could have allowed diagnosis of MS immediately, i.e. earlier than with the Mc Donald criteria.

CONCLUSIONS

The evaluation of FLC-k with hyperbolic reference range in quotient diagrams is superior to other analytical methods like the linear FLC-k index. We suggest a sequential CSF testing with FLC-k Reibergram evaluation, potentially followed by isoelectric focusing. With the MRZ reaction we obtain highest specificity for MS diagnosis.

Clinical Use of κ Free Light Chains Index as a Screening Test for Multiple Sclerosis

Objective

To assess the usefulness of the κ free light chain index (κFLCi) as a screening test to identify patients with suspected MS.

Methods

The study included 56 patients with a request to test for oligoclonal bands (OCBs). OCBs were detected by isoelectric focusing, followed by immunofixation. Cerebrospinal fluid (CSF) and serum κFLC were measured by a turbidimetric assay. Also, the κFLC index (κFLCi) was calculated.

Results

CSF κFLC levels and κFLCi were significantly higher in patients with multiple sclerosis (MS) than in patients with other neurological diseases (NDs; P &lt; .001 and P &lt; .001, respectively). At the cutoff value of 2.9, the κFLCi detected MS with sensitivity of 97% and specificity of 65%. Overall, 92% patients with κFLCi of 2.9 or greater and who had tested positive for OCBs were diagnosed as having MS.

Conclusion

Our findings support the use of κFLCi as a screening test when MS is suspected, followed by OCB detection as a confirmatory test for the diagnosis of MS.

Reiber's Diagram for Kappa Free Light Chains: The New Standard for Assessing Intrathecal Synthesis?

Oligoclonal bands are the gold standard for determination of an intrathecal immunoglobulin G synthesis and were recently included in the McDonald criteria of 2017 to diagnose relapsing multiple sclerosis (MS) as a substitute for dissemination in time. Intrathecally produced kappa free light chains (KFLC) are a novel promising biomarker with similar characteristics and the advantage for automated determination. However, different approaches exist to determine the intrathecal KFLC fraction. The most common method is to calculate the CSF/serum KFLC quotient with reference to the albumin CSF/serum quotient (QKappa/QAlb) the so-called KFLC index. Recently, Reiber developed a theoretically and empirically founded hyperbolic function similar to his traditional hyperbolic function for the immunoglobulins A, G, M. Our study included a total of 168 patients with either MS according to the McDonald criteria of 2017, clinically isolated syndrome (CIS) with conversion to MS during follow-up, or stable CIS. Positive oligoclonal bands were compared with the KFLC index, Reiber's KFLC diagram, Presslauer's KFLC exponential curve, and Senel's linear curve for KFLC. Reiber's diagram detected an intrathecal production of KFLC in 98/100 patients with MS, only one patient fewer than oligoclonal bands positivity (99/100). By using the KFLC index ≥ 5.9, Presslauer's KFLC exponential function, and Senel's linear curve two more patients would not have been identified (96/100). For the group of patients who converted from CIS to MS similar results were obtained for both the oligoclonal bands and the Reiber graph (21/24, 88%). The KFLC index ≥ 5.9, Presslauer's method, and Senel's linear function each identified two patients fewer (19/24, 79%). In patients with stable CIS, 11/44 patients (25%) displayed oligoclonal bands in contrast to 9/44 patients (20%) with elevated KFLC by using Reiber's diagram and Presslauer's method, 8/44 patients (18%) with elevated KFLC as detected by Senel's linear function, and 7/44 patients (16%) with KFLC index ≥ 5.9. In conclusion, Reiber's KFLC diagram shows a great diagnostic performance to detect an intrathecal KFLC production in patients with MS.

Cerebrospinal fluid free light chains compared to oligoclonal bands as biomarkers in multiple sclerosis

Cerebrospinal fluid (CSF) free light chains (FLC) may be an alternative biomarker to oligoclonal bands (OCB) in multiple sclerosis (MS). Herein, we compared the diagnostic accuracy of CSF OCB and FLC and we tested the prognostic value of FLC in a cohort of 64 MS patients and 106 controls. A κ-index >7.83 was more sensitive but less specific than OCB in discriminating MS patients from controls. Additionally, a κ-index >10.61 performed better than OCB in the discrimination between MS and controls with inflammatory neurological diseases (p < .001). In clinically isolated syndrome (CIS) patients, a κ-index >10.61 significantly predicted time to conversion to MS (p = .020). κ-index might be a valid alternative to OCB as a diagnostic biomarker for MS and might also be a prognostic marker in CIS.

Association of cerebrospinal fluid kappa free light chains with the intrathecal polyspecific antiviral immune response in multiple sclerosis

The polyspecific B-lymphocyte response to neurotropic viruses such as measles (M), rubella (R) and varicella zoster (Z), known as MRZ reaction, is to-date the most specific neurochemical marker for multiple sclerosis (MS). The aim of this study was to investigate a possible association of immunoglobulin (Ig) kappa (κ-) and lambda (λ-) free light chains (FLC) with the presence of the MRZ reaction in multiple sclerosis. Immunoglobulin κ- and λ-FLC, MRZ reaction, oligoclonal IgG bands (OCB), and cerebrospinal fluid (CSF) routine parameters were measured in 65 MS patients. OCB were detected in 97% of MS patients, intrathecal IgG synthesis according to Reiber was detectable in 57%, an elevated IgG index (>0.7) in 66% and the MRZR was positive in 45%. All investigated κ-values (CSF κFLC, CSF-serum ratio of κFLCs (QκFLC), and κFLC index (κFLC/QAlbumin)) were significantly higher in patients with positive MRZ reaction as compared to MRZ negative MS patients. In contrast, λ-values showed no significant differences. Additionally to the putative diagnostic sensitivity and prognostic value of κFLC, the association of κFLC with a highly specific neurochemical marker for MS - the MRZ reaction, especially the determination of κFLCs is an informative tool to assess the B-cell response and determine its extent in MS patients.

Diagnostic relevance of free light chains in cerebrospinal fluid - The hyperbolic reference range for reliable data interpretation in quotient diagrams

BACKGROUND

Free light chains, type kappa (FLC-K), in cerebrospinal fluid (CSF) were compared to oligoclonal IgG in many studies for sensitive detection of immune reactions in brain. The missing consensus about CSF data interpretation prevents reliable conclusions. This can be overcome by a theory-based hyperbolic reference range in CSF/serum quotient diagrams.

METHODS

Mean Quotients for FLC-K, Q_Kappa, and albumin, QAlb, of grouped, biochemically defined controls (N = 433) are fitted with the hyperbolic function Q_Kappa(mean) = a/b (QAlb² + b²)^0.5 - c by a generally applicable procedure excluding outliers.

RESULTS

With Q_Kappa(mean), the coefficient of variation CV (22.5%) and the reference range (Q_Kappa(mean) ± 3 CV) we got the discrimination line Q_Kappa(lim) = (3.27(QAlb² + 33)^0.5-8.2) ×10^-3 in a FLC-K Reibergram. Intrathecal FLC-K was found in 8% of another control group without OCB (N = 388) but was missed in 7% of patients with definite Multiple sclerosis (N = 95). In MS the mean intrathecal fraction was threefold larger for FLC-K (95%) compared to total IgG (36%). Similar mean quantities of intrathecal FLC-K contradict an immunological conversion between a Clinically isolated syndrome and MS.

DISCUSSION

The hyperbolic reference range is superior to linear FLC-K Index (10 to 15% false negatives) and exponential curves (30% false positive interpretations for controls) in the analytical range of MS data, with excellent data fit for up to ten-fold larger QAlb values. Dynamics of the small molecule FLC-K contribute to the understanding of molecular size dependent barrier functions.

Cerebrospinal fluid free light chains as diagnostic biomarker in neuroborreliosis

BACKGROUND

Free light chains (FLC) have been proposed as diagnostic biomarker in patients with inflammatory central nervous system diseases. The objective of this study was to investigate the diagnostic utility of intrathecal κ- and λ-FLC synthesis in patients with neuroborreliosis.

METHODS

κ- and λ-FLC were measured by nephelometry under blinded conditions in cerebrospinal fluid (CSF) and serum sample pairs of 34 patients with neuroborreliosis and compared to a cohort of 420 control patients. κ-FLC index was calculated as [CSF κ-FLC/serum κ-FLC]/[CSF albumin/serum albumin], and λ-FLC index in analogy.

RESULTS

κ-FLC and λ-FLC index were significantly elevated in patients with neuroborreliosis compared to the control group. At a specificity level of 95%, κ-FLC and λ-FLC index showed a diagnostic sensitivity of 88.2% and 100%. In comparison, IgM and IgG synthesis according to Reiber formula, IgG index >0.7 and OCB status reached a sensitivity of 83.9%, 44.1%, 58.8% and 64.7%.

CONCLUSION

These findings support the diagnostic value of intrathecal FLC synthesis in neuroborreliosis patients and demonstrate a valid, easy and rater-independent alternative for the detection of an intrathecal immunoglobulin production.