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.

Inter-assay diagnostic accuracy of cerebrospinal fluid kappa free light chains for the diagnosis of multiple sclerosis

Background

Cerebrospinal fluid (CSF) kappa free light chain (κFLC) measures gained increasing interest as diagnostic markers in multiple sclerosis (MS). However, the lack of studies comparing assay-dependent diagnostic cutoff values hinders their use in clinical practice. Additionally, the optimal κFLC parameter for identifying MS remains a subject of ongoing debate.

Objectives

The aim of this study was to compare same-sample diagnostic accuracies of the κFLC index, κIgG index, CSF κFLC/IgG ratio, and isolated CSF κFLC (iCSF-κFLC) between two reference centers using different methods.

Methods

Paired serum and CSF samples were analyzed for κFLC and albumin concentrations by Freelite®-Optilite (Sint-Jan Bruges hospital) and N Latex®-BNII (Ghent University hospital). Diagnostic performance to differentiate MS from controls was assessed using ROC curve analysis.

Results

A total of 263 participants were included (MS, n = 80). Optimal diagnostic cutoff values for the κFLC index (Freelite®-Optilite: 7.7; N Latex®-BNII: 4.71), κIgG index (Freelite®-Optilite: 14.15, N Latex®-BNII: 12.19), and CSF κFLC/IgG ratio (Freelite®-Optilite: 2.27; N Latex®-BNII: 1.44) differed between the two methods. Sensitivities related to optimal cutoff values were 89.9% (Freelite®-Optilite) versus 94.6% (N Latex®-BNII) for the κFLC index, 91% (Freelite®-Optilite) versus 92.2% (N Latex®-BNII) for the κIgG index, and 81.3% (Freelite®-Optilite) versus 91.4% (N Latex®-BNII) for the CSF κFLC/IgG ratio. However, for iCSF-κFLC, optimal diagnostic cutoff values (0.36 mg/L) and related specificities (81.8%) were identical with a related diagnostic sensitivity of 89.9% for Freelite®-Optilite and 90.5% for N Latex®-BNII. The diagnostic performance of the κFLC index [area under the curve (AUC) Freelite®-Optilite: 0.924; N Latex®-BNII: 0.962] and κIgG index (AUC Freelite®-Optilite: 0.929; N Latex®-BNII: 0.961) was superior compared to CSF oligoclonal bands (AUC: 0.898, sensitivity: 83.8%, specificity: 95.9%).

Conclusions

The κFLC index and the κIgG index seem to be excellent markers for identifying MS, irrespective of the method used for κFLC quantification. Based on the AUC, they appear to be the measures of choice. For all measures, optimal cutoff values differed between methods except for iCSF-κFLC. iCSF-κFLC might therefore serve as a method-independent, more cost-efficient, initial screening measure for MS. These findings are particularly relevant for clinical practice given the potential future implementation of intrathecal κFLC synthesis in MS diagnostic criteria and for future multicentre studies pooling data on κFLC measures.

Multiple Sclerosis Diagnostic Delay and Misdiagnosis

Multiple sclerosis (MS) misdiagnosis in the form of an incorrect diagnosis of MS, as well as delayed diagnosis in patients who do have MS, both influence patient clinical outcomes. Contemporary studies have reported data on factors associated with these diagnostic challenges and their frequency. Expediting diagnosis in patients with MS and reducing MS misdiagnosis in patients who do not have MS may be aided by educational efforts surrounding early MS symptoms and proper application of MS diagnostic criteria. Emerging novel MS diagnostic biomarkers may aid early and accurate diagnosis of MS in the future.

Free light chains as a reliable biomarker of intrathecal synthesis in the diagnosis of CNS inflammatory diseases

OBJECTIVE

To address the diagnostic performances of cerebrospinal fluid (CSF) free light chains (FLC) measurements compared to oligoclonal bands (OCB) to support multiple sclerosis (MS) diagnosis.

RESULTS

kFLC index showed the highest diagnostic accuracy to detect MS patients with the highest AUC compared to OCB, IgG index, IF kFLC R, kFLC H, λFLC index and IF λFLC.

CONCLUSIONS

FLC indices are biomarkers of intrathecal Immunoglobulin synthesis and central nervous system (CNS) inflammation. kFLC index can discriminate between MS and other CNS inflammatory disorders, while λFLC index is less informative for MS but can play a role to support the diagnosis of other inflammatory CNS disorders.

Diagnostic significance of IgG and albumin indices versus oligoclonal band types in demyelinating disorders

AIMS

The laboratory diagnosis of demyelinating inflammatory disorders (DIDs) relies on both intrathecal oligoclonal band (OCB) positivity and IgG index. Although OCB typing remains the gold-standard test for DIDs, it can be laborious and ambiguous, complicating diagnostics, and unduly increasing diagnostic time. We examined whether serum or cerebrospinal fluid (CSF) parameters can classify OCB types and, thus, be used as a replacement test to standard OCB typing.

METHODS

We retrospectively analysed >1000 prospectively collected samples of patients with DIDs and quantified albumin and IgG levels in the CSF and serum. We determined OCB types by isoelectric focusing combined with immunofixation and evaluated the diagnostic accuracies of IgG and albumin indices in discriminating OCB types by receiver operating characteristic curves and multinomial regression.

RESULTS

An IgG index cut-off of 0.589 differentiated types 2/3 from types 1/4 (area under the curve 0.780, 95% CI 0.761 to 0.812, p<0.001; specificity: 71.10%, sensitivity: 73.45%). Albumin quotient cut-off values of 6.625 and of 6.707 discriminated type 1 from type 4 and type 2 from type 3, respectively (specificity: <55%, sensitivity: <75%). Female sex, age, IgG index, CSF IgG and serum albumin were associated with different OCB types.

CONCLUSIONS

Our study reveals that IgG and albumin index can differentiate OCB types with adequate accuracy, especially if refined by age and gender.

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.

Novel CSF Biomarkers Tracking Autoimmune Inflammatory and Neurodegenerative Aspects of CNS Diseases

The accurate diagnosis of neuroinflammatory (NIDs) and neurodegenerative (NDDs) diseases and the stratification of patients into disease subgroups with distinct disease-related characteristics that reflect the underlying pathology represents an unmet clinical need that is of particular interest in the era of emerging disease-modifying therapies (DMT). Proper patient selection for clinical trials and identifying those in the prodromal stages of the diseases or those at high risk will pave the way for precision medicine approaches and halt neuroinflammation and/or neurodegeneration in early stages where this is possible. Towards this direction, novel cerebrospinal fluid (CSF) biomarker candidates were developed to reflect the diseased organ's pathology better. Μisfolded protein accumulation, microglial activation, synaptic dysfunction, and finally, neuronal death are some of the pathophysiological aspects captured by these biomarkers to support proper diagnosis and screening. We also describe advances in the field of molecular biomarkers, including miRNAs and extracellular nucleic acids known as cell-free DNA and mitochondrial DNA molecules. Here we review the most important of these novel CSF biomarkers of NIDs and NDDs, focusing on their involvement in disease development and emphasizing their ability to define homogeneous disease phenotypes and track potential treatment outcomes that can be mirrored in the CSF compartment.

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).

An Update on Diagnostic Laboratory Biomarkers for Multiple Sclerosis

PURPOSE

For many patients, the multiple sclerosis (MS) diagnostic process can be lengthy, costly, and fraught with error. Recent research aims to address the unmet need for an accurate and simple diagnostic process through discovery of novel diagnostic biomarkers. This review summarizes recent studies on MS diagnostic fluid biomarkers, with a focus on blood biomarkers, and includes discussion of technical limitations and practical applicability.

RECENT FINDINGS

This line of research is in its early days. Accurate and easily obtainable biomarkers for MS have not yet been identified and validated, but several approaches to uncover them are underway. Continue efforts to define laboratory diagnostic biomarkers are likely to play an increasingly important role in defining MS at the earliest stages, leading to better long-term clinical outcomes.

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.

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 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.

Kappa free light chain index as a diagnostic biomarker in multiple sclerosis: A real-world investigation

Kappa free light chain (KFLC) index, a measure for intrathecal production of free kappa chains, has been increasingly recognized for its diagnostic potential in multiple sclerosis (MS) as a quantitative alternative to IgG oligoclonal bands (OCBs). Our objective was to investigate the sensitivity, specificity, and overall diagnostic accuracy of KFLC index in MS. KFLC index was prospectively determined as part of the diagnostic workup in patients with suspected MS (n = 327) between May 2013 and February 2020. Patients with clinically isolated syndrome (CIS), radiologically isolated syndrome (RIS), and MS had markedly higher KFLC index (44.6, IQR 16-128) compared with subjects with other neuro-inflammatory disorders (ONID) and symptomatic controls (SC) (2.19, IQR 1.68-2.98, p < 0.001). KFLC index had a sensitivity of 0.93 (95% CI 0.88-0.95) and specificity of 0.87 (95% CI 0.8-0.92) to discriminate CIS/RIS/MS from ONID and SC (AUC 0.94, 95% CI 0.91-0.97, p < 0.001). KFLC index and intrathecal fraction (IF) KFLC had similar accuracies to detect MS. Treatment with disease-modifying therapy (DMT) did not influence the level of KFLC index and it was not affected by demographic factors or associated with degenerative or inflammatory biomarkers in cerebrospinal fluid (CSF). KFLC index in MS diagnostics has methodological advantages compared to OCB and is independent to subjective interpretation. Moreover, it is an attractive diagnostic tool since the diagnostic specificity and sensitivity of KFLC index are similar with that of OCBs and KFLC_IF and better than for IgG index. We show that KFLC index was influenced neither by DMT nor by demographic factors or other inflammatory or degenerative processes in MS as determined by biomarkers in CSF.

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.

Diagnostic performance of cerebrospinal fluid free light chains in Lyme neuroborreliosis - a pilot study

Background The aim of this study was to evaluate the diagnostic performance of cerebrospinal fluid (CSF) free light chains (FLCs) in the diagnosis of Lyme neuroborreliosis (LNB). Methods Serum and CSF levels of κ- and λ-FLC, albumin and total concentration of immunoglobulin M (IgM) were determined together with CSF chemokine CXCL13 in 23 patients with definite LNB, 35 inflammatory neurological disease control (INDC) and 18 non-inflammatory control (NIC) patients. Indices and intrathecal fractions (IFs) of FLC and IgM were calculated. Results Significant differences in FLC indices and IFs were found between the LNB group and both control groups, p ≤ 0.007. Sensitivity of intrathecal κ- and λ-FLC synthesis reached 78%-87% in LNB patients with a specificity of 94%-100% in NIC patients, whereas specificity in INDC patients was 69%. The corresponding frequencies of positive results for IF and index of IgM and CSF CXCL13 in these three diagnostic groups were 74%-96% in LNB patients, 0% in NIC patients and 3%-6% in INDC patients at the chosen cut-off levels. Conclusions The findings of this study show a moderate to high sensitivity of CSF κ- and λ-FLC in LNB patients with a high specificity in NIC patients. However, overlap in CSF κ- and λ-FLC levels between LNB and INDC patients calls for caution in the interpretation and limits the diagnostic usefulness in the LNB diagnosis. CSF CXCL13 appears to be the most valuable additional biomarker of LNB aside from routine parameters such as CSF pleocytosis and anti-Borrelia antibody index.

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.

Saliva immunoglobulin free light chain analysis for monitoring disease activity and response to treatment in multiple sclerosis

BACKGROUND

Immunoglobulin free light chains (FLC) have recently gained considerable interest as new promising intrathecal biomarkers of multiple sclerosis (MS). However, lumbar puncture is invasive and not practical for monitoring disease course. This study aimed to assess the utility of saliva FLC as a biomarker of disease activity and response to treatment in MS METHODS: Western blotting was used to study saliva FLC monomers and dimers. The intensity of immunoreactive FLC bands was quantified by electrophoresis analysis, and the obtained values were used as FLC indices to account for kappa and lambda FLC monomer and dimer levels. Firth's logistic regression analysis suitable to study small cohorts was applied to compare FLC levels between M.S. patients in relapse, MS patients in remission, and healthy controls. Association between FLC levels and clinical and radiological parameters was analyzed.

RESULTS

55 MS patients and 40 healthy controls were evaluated. Saliva FLC levels were significantly higher in relapse compared to remission. Logistic regression analysis employing a combination of FLC indices confirmed the significant difference between these two groups. The FLC levels were significantly reduced by treatment with corticosteroids. During remission, patients treated with disease-modifying therapies had lower levels of FLC compared to untreated patients. The increased FLC levels were associated with the presence of gadolinium-enhancing lesions, but not with MRI T2 lesion load and EDSS scores. During individual patient follow-up, the changes of the saliva FLC levels were in concordance with the disease activity status.

CONCLUSIONS

Saliva FLC levels may be a useful biomarker for discriminating between stable remission and active disease. The developed test may serve as a new, non-invasive, and inexpensive tool for monitoring disease activity and response to treatment in MS.

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 Analysis in Multiple Sclerosis Diagnosis: An Update

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system (CNS) with brain neurodegeneration. MS patients present heterogeneous clinical manifestations in which both genetic and environmental factors are involved. The diagnosis is very complex due to the high heterogeneity of the pathophysiology of the disease. The diagnostic criteria have been modified several times over the years. Basically, they include clinical symptoms, presence of typical lesions detected by magnetic resonance imaging (MRI), and laboratory findings. The analysis of cerebrospinal fluid (CSF) allows an evaluation of inflammatory processes circumscribed to the CNS and reflects changes in the immunological pattern due to the progression of the pathology, being fundamental in the diagnosis and monitoring of MS. The detection of the oligoclonal bands (OCBs) in both CSF and serum is recognized as the “gold standard” for laboratory diagnosis of MS, though presents analytical limitations. Indeed, current protocols for OCBs assay are time-consuming and require an operator-dependent interpretation. In recent years, the quantification of free light chain (FLC) in CSF has emerged to assist clinicians in the diagnosis of MS. This article reviews the current knowledge on CSF biomarkers used in the diagnosis of MS, in particular on the validated assays and on the alternative biomarkers of intrathecal synthesis.

The clinical significance of single or double bands in cerebrospinal fluid isoelectric focusing. A retrospective study and systematic review

BACKGROUND

The presence of ≥3 oligoclonal bands (OCB) in the cerebrospinal fluid (CSF) without corresponding bands in serum represents a definite pathological pattern, whereas the clinical significance of 1-2 CSF bands (borderline pattern) is poorly investigated.

METHODS

We screened 1986 consecutive CSF and serum samples which were collected over a four-year time period and had results of isoelectric focusing (IEF) available. Of patients with borderline OCB we reviewed individual medical charts for assessment of clinical diagnoses. Where feasible, IEF was replicated and results of follow-up samples were obtained. IEF was performed using polyacrylamide gel followed by immunoblotting and IgG-specific antibody staining. Additionally, we performed a systematic literature review of the diagnostic specificity of OCB using different cut-offs for CSF-restricted bands.

RESULTS

Out of 253 patients with borderline OCB, 21.7% had an inflammatory neurological disease (IND) of the central nervous system, comprising 4% multiple sclerosis patients, and 14.2% had a peripheral IND, whereas the remaining 64.1% of patients showed non-inflammatory diseases. Frequency of one or two CSF bands without corresponding serum bands did not differ between the disease groups. In a subgroup of 100 patients IEF was repeated. Of those, 73% were OCB negative, while no sample was positive. In 26 patients IEF results were available of a follow-up sample collected after a median of 27 months. Of those, 4 (15.4%) turned positive. Systematic literature review revealed a diagnostic specificity of OCB of 97% and 92% using a cut-off ≥3 and ≥2 CSF bands in patients with mainly non-inflammatory neurological diseases.

CONCLUSION

The clinical significance of one or two CSF-restricted bands is moderate and, hence, indicates a possible but not reliable proof of intrathecal B-cell activity. Sample re-testing, introduction of an additional diagnostic category, e.g. "possible intrathecal IgG synthesis", and follow-up lumbar puncture might be possible options to address this scenario.