A multicenter study on the diagnostic significance of a single cerebrospinal fluid IgG band

Kappa index in the diagnostic work-up of autoimmune encephalitis

BACKGROUND

The presence of inflammatory changes in the cerebrospinal fluid (CSF), including immunoglobulin intrathecal synthesis (IS), can support the diagnosis of autoimmune encephalitis (AE) and allow prompt treatment. The main aim of our study was to calculate the Kappa index as a marker of IS, in patients with AE.

METHODS

Charts of patients undergoing a diagnostic work-up for suspected AE between 2009 and 2023 were reviewed and the Graus criteria applied. CSF and serum kappa free light chains were determined using the Freelite assay (The Binding Site Group) and the turbidimetric Optilite analyzer.

RESULTS

We identified 34 patients with "definite" AE (9 anti-NMDAR AE and 25 limbic AE) and nine patients with "possible" AE. Five patients (15%) with definite AE had pleocytosis and twelve (34%) showed CSF-restricted oligoclonal bands (OCB) at isoelectric focusing. The Kappa index was >6 in 29.4% and > 3 in 50% of the definite AE patients. It was elevated (>3) in 36.4% of patients with definite AE who resulted negative to OCB testing and was the only altered parameter suggestive of an ongoing inflammatory process in the CNS in three definite AE patients with otherwise normal CSF findings (i.e. normal cell count and protein levels, no OCBs). In the possible AE group, one patient had a Kappa index >3 in the absence of OCB.

CONCLUSIONS

The Kappa index could be useful, as a more sensitive marker of IS and as a supportive marker of neuroinflammation, in the diagnostic work-up of suspected AE.

Do we still need OCBs in MS diagnosis and how many?

BACKGROUND

CSF-specific oligoclonal bands (CSF-OCBs) can be used for dissemination in time (DIT) in the 2017 multiple sclerosis (MS) diagnostic criteria. A cut-off of ≥2 CSF-OCBs was recommended but studies have suggested ≥3 CSF-OCBs may be superior.

OBJECTIVES

To assess utility of ≥2 and ≥3 CSF-OCBs as a cut-off for MS diagnosis.

METHODS

Paired serum and CSF-OCBs sent to the Walton Centre, UK between July 2018 and June 2020 were included. CSF-OCBs were assessed using isoelectric focussing and reviewed by two blinded raters. Case records were reviewed.

RESULTS

Of 1334 paired serum and CSF-OCB requests, 945 cases had sufficient clinical information. More than 1 CSF-OCB was detected in 268/945(28%) cases. Of these, 252 had ≥2 and 230 had ≥3 CSF-OCBs. The sensitivity and specificity for MS with ≥2 and ≥3 CSF-OCBs were 91.7%, 91.2%, 90.2% and 93.8% respectively. Only 3/22 patients with 2 CSF-OCBs had MS. In 25% of patients, CSF-OCBs reduced time to MS diagnosis (median 437.5 days (28-1332)).

CONCLUSION

Although cut-offs of ≥2 or ≥3 CSF-OCBs performed similarly well, 2 CSF-OCBs were frequently seen with non-inflammatory pathology. Use of ≥3 CSF-OCBs for MS diagnosis should be considered. CSF analysis reduced time to MS diagnosis by approximately 14 months.

Variation in Processes and Reporting of Cerebrospinal Fluid Oligoclonal Banding and Associated Tests and Calculated Indices across Canadian Clinical Laboratories

OBJECTIVES

Multiple sclerosis is diagnosed based on clinical and laboratory findings, including cerebrospinal fluid (CSF) oligoclonal banding (OCB) analysis. The lack of updated CSF OCB laboratory guidelines in Canada has likely led to variation in processes and reporting across clinical laboratories. As a first step to developing harmonized laboratory recommendations, we examined current CSF OCB processes, reporting, and interpretation across all Canadian clinical laboratories currently performing this test.

DESIGN AND METHODS

A survey of 39 questions was sent to clinical chemists at all 13 Canadian clinical laboratories performing CSF OCB analysis. The survey included questions regarding quality control processes, reporting practices for CSF gel electrophoresis pattern interpretation, and associated tests and calculated indices.

RESULTS

The survey response rate was 100%. Most (10/13) laboratories use ≥2 CSF-specific bands (2017 McDonald Criteria) as their CSF OCB positivity cut-off and only 2/13 report the number of bands with every report. Most (8/13 and 9/13) laboratories report an inflammatory response pattern and monoclonal gammopathy pattern, respectively. However, the process for reporting and/or confirming a monoclonal gammopathy varies widely. Variation was observed for reference intervals, units, and the panel of reported associated tests and calculated indices. The maximum acceptable time interval between paired CSF and serum collections varied from 24 hours to no limit.

CONCLUSIONS

Profound variation exists in processes, reporting, and interpretation of CSF OCB and associated tests and indices across Canadian clinical laboratories. Harmonization of CSF OCB analysis is required to ensure continuity and quality of patient care. Our detailed assessment of current practice variation highlights the need for clinical stakeholder engagement and further data analysis to support optimal interpretation and reporting practices, which will aid in developing harmonized laboratory recommendations.

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.

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.

Oligoclonal IgG bands in chronic inflammatory polyradiculoneuropathies

BACKGROUND

Cerebrospinal fluid (CSF) albumincytologic dissociation represents a supportive diagnostic criterion of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP).Few studies have investigated possible systemic or intrathecal humoral immune response activation in CIDP.Aim of our study was to investigate whether the search of oligoclonal IgG bands (OCBs) might provide additional data helpful in CIDP diagnostic work-up.

METHODS

Forty-eight consecutive patients with CIDP (34 men, mean age 59.4, range 16-83) were recruited. CSF analysis included nephelometric measurement of albumin and IgG concentrations, calculation of Q_ALB, QAlb_LIM and intrathecal IgG synthesis, and OCBs detection with isoelectric focusing. Data were compared with those from CSF and serum of 32 patients with Guillain-Barré syndrome (GBS), 18 patients with anti-myelin associated glycoprotein (MAG) antibody neuropathy, 4 patients with multifocal motor neuropathy and 32 patients with non-inflammatory neuropathies (NINPs).

RESULTS

Patients with CIDP and anti-MAG antibody neuropathy had significantly higher CSF albumin concentrations and Q_ALB values than NINPs (p=0.0003 and p=0.0095, respectively). A total of 9 (19%) patients with CIDP presented identical serum and CSF OCBs ('mirror pattern') versus 3 patients (16.6%) with anti-MAG antibody neuropathy, 13 patients (40.6%) with GBS and 12.5% patients with NINPs. Only one patient with CIDP showed unique-to-CSF OCBs. First-line therapy was effective in 80.4% of patients with CIDP, irrespective of CSF findings.

CONCLUSIONS

Compared with NINP, CIDP, GBS and anti-MAG antibody neuropathies had a significantly increased CSF protein and blood-spinal nerve root barrier damage. Intrathecal humoral immune response is rare in our patients with CIDP. Systemic oligoclonal activation is more frequent, but not significantly different from what was detected in the control groups.

Early multiple sclerosis: diagnostic challenges in clinically and radiologically isolated syndrome patients

PURPOSE OF REVIEW

With the introduction of new diagnostic criteria, the sensibility for multiple sclerosis (MS) diagnosis increased and the number of cases with the clinically isolated syndrome (CIS) decreased. Nevertheless, a misdiagnosis might always be around the corner, and the exclusion of a 'better explanation' is mandatory.There is a pressing need to provide an update on the main prognostic factors that increase the risk of conversion from CIS or from radiologically isolated syndrome (RIS) to MS, and on the potential 'red flags' to consider during the diagnostic workup.

RECENT FINDINGS

We discuss diagnostic challenges when facing patients presenting with a first demyelinating attack or with a RIS, with a focus on recently revised diagnostic criteria, on other neuroinflammatory conditions to be considered in the differential diagnosis and on factors distinguishing patients at risk of developing MS.A correct definition of a 'typical' demyelinating attack, as well as a correct interpretation of MRI findings, remains crucial in the diagnostic process. The cerebrospinal fluid examination is warmly recommended to confirm the dissemination in time of the demyelinating process and to increase the diagnostic accuracy.

SUMMARY

An early and accurate diagnosis of MS requires careful consideration of all clinical, paraclinical and radiological data, as well the reliable exclusion of other mimicking pathological conditions. This is advocated to promptly initiate an appropriate disease-modifying therapy, which can impact positively on the long-term outcome of the disease.

Clinical significance of a single cerebrospinal fluid immunoglobulin band: A retrospective study

BACKGROUND

To demonstrate an inflammatory process in the central nervous system, the presence of at least two immunoglobulin (Ig) bands in the cerebrospinal fluid (CSF) is required. So far, the presence of a single abnormal Ig band is considered as negative.

OBJECTIVE

The objective was to assess retrospectively the significance of a single CSF Ig band in clinical practice.

METHODS AND RESULTS

Out of 10,286 CSF analyses, we retained 214 results with single Ig. An inflammatory neurological disorder was diagnosed in 41% of patients.

CONCLUSION

Despite a modest sensitivity, the presence of a single CSF Ig band may be a biomarker of an inflammatory mechanism and, as such, may prompt the clinician to repeat the analysis when the clinical context remains suggestive.

Kappa Index Versus CSF Oligoclonal Bands in Predicting Multiple Sclerosis and Infectious/Inflammatory CNS Disorders

Background: Cerebrospinal fluid (CSF) kappa free light chains (KFLC) are gaining increasing interest as markers of intrathecal immunoglobulin synthesis. The main aim of this study was to assess the diagnostic accuracy (AUC) of the kappa index (CSF/serum KFLC divided by the CSF/serum albumin ratio) compared to CSF oligoclonal IgG bands (OCB) in predicting Multiple Sclerosis (MS) or a central nervous system infectious/inflammatory disorder (CNSID). Methods: We enrolled patients who underwent a diagnostic spinal tap throughout two years. KFLC levels were determined using a Freelite assay (Binding Site) and the turbidimetric Optilite analyzer. Results: Of 540 included patients, 223 had a CNSID, and 84 had MS. The kappa index was more sensitive (0.89 versus 0.85) and less specific (0.84 versus 0.89), with the same AUC (0.87) as OCB for MS diagnosis (optimal cut-off: 6.2). Adding patients with a single CSF IgG band to the OCB-positive group slightly increased the AUC (0.88). Likewise, the kappa index (cut-off: 3.9) was more sensitive (0.67 versus 0.50) and less specific (0.81 versus 0.97), with the same AUC (0.74) as OCB, for a CNSID diagnosis. Conclusion: The kappa index and CSF OCB have comparable diagnostic accuracies for a MS or CNSID diagnosis and supply the clinician with useful, complementary information.

Cerebrospinal fluid oligoclonal IgM test in routine practice: Comparison with quantitative assessment of intrathecal IgM synthesis

BACKGROUND

Intrathecal IgM synthesis demonstrated either as cerebrospinal fluid (CSF)-restricted oligoclonal (o-) IgM bands or calculated using various formulas has been linked to more aggressive multiple sclerosis (MS) course. However, the proportion of MS patients showing intrathecal IgM synthesis varies largely between studies. We aimed to explore the relation between different formulas and results of o-IgM, and to assess the frequency of o-IgM bands in an unselected series of samples.

METHODS

432 samples were analyzed for o-IgM, o-IgG and quantitative measures of IgM and IgG synthesis. IgM index and formulas of Reiber, Auer and Öhman were compared to the result of the o-IgM test.

RESULTS

At the cut-off commonly used, the non-linear formulas for intrathecal synthesis were specific (>94%) but rather insensitive (<40% even at a cut-off of 4 CSF-restricted bands) compared to o-IgM. No significant difference was noted in the performance of different formulas. At a cut-off of 4 bands, 61% of MS patients, but none of the controls were positive for o-IgM.

CONCLUSIONS

Formulas for intrathecal IgM synthesis are insensitive compared to o-IgM. We propose to evaluate samples with 2 or 3 extra-CSF IgM bands as borderline and only samples with 4 or more as definitely positive.

Diagnostic value of kappa free light chains in patients with one isolated band in isoelectric focusing

OBJECTIVES

Oligoclonal band (OCB) determination in cerebrospinal fluid (CSF) is the gold standard to detect intrathecal inflammation. However, there is uncertainty about the significance of one isolated band in CSF. Free light chains kappa (FLC-k) are gaining interest as a complementary method to detect intrathecal inflammation. The aim of this study was to investigate the performance of an additive measurement of FLC-k in patients with one isolated band in CSF.

MATERIALS & METHODS

FLC-k were analyzed using the nephelometric Siemens FLC-k kit in paired samples of CSF and sera (n = 56) in patients with one isolated band in isoelectric focusing. According to medical diagnosis, samples were subdivided in inflammatory neurological disease, non-inflammatory neurological disease controls and symptomatic controls. Intrathecal fraction of FLC-k was plotted in a FLC-k quotient diagram. OCB interpretation was done blinded by three experienced raters.

RESULTS

Of 6695 OCB analyses, 91 (1.4%) had one isolated band in CSF. After exclusion of patient samples due to unclear OCB pattern after reevaluation and sample availability, 56 patient samples were included in the study. All patients with an inflammatory origin of disease (n = 13) had FLC-k values above the upper discrimination line (Qlim) in the FLC-k quotient diagram, resulting in a sensitivity of 100% with a positive predictive value of 52% and a negative predictive value of 100%. Fourteen patients (36%) with a non-inflammatory origin of disease (n = 39) had FLC-k values above Qlim.

CONCLUSIONS

In patients with one isolated band in CSF, a lack of intrathecal fraction of FLC-k strongly favors a non-inflammatory orgin of disease. Implementation of FLC-k measurement can help the clinician in the diagnostic process of neurological diseases.

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.

Cerebrospinal fluid analysis and the determination of oligoclonal bands

This document presents the guidelines for the cerebrospinal fluid (CSF) analysis and the determination of oligoclonal bands (OCBs) as pivotal tests in neuroinflammatory pathologies of the central nervous system. The guidelines have been developed following a consensus process built on questionnaire-based surveys, internet contacts, and discussions at workshops of the sponsoring Italian Association of Neuroimmunology (AINI) congresses. Essential clinical information on the pathologies in which the CSF analysis is indicated, and, particularly, on those characterized by the presence of OCBs in the intrathecal compartment, indications and limits of CSF analysis and OCB determination, instructions for result interpretation, and agreed laboratory protocols (Appendix) are reported for the communicative community of neurologists and clinical pathologists.