High sensitivity and specificity of elevated cerebrospinal fluid kappa free light chains in suspected multiple sclerosis

Multiple sclerosis: assay of free immunoglobulin light chains

Over the past five years, a number of papers have appeared describing the assay of free immunoglobulin light chains in cerebrospinal fluid to assist in the diagnosis of multiple sclerosis. The assay of kappa free immunoglobulin chains is being advocated as a technically simpler and cheaper quantitative alternative to the qualitative detection of oligoclonal bands. This article reviews the analytical and clinical characteristics of these immunoglobulin free light chain assays and places them in their historical context and possible future developments.

[Cerebrospinal fluid diagnostics in multiple sclerosis]

As a chronic inflammatory disease of the central nervous system (CNS), multiple sclerosis (MS) is associated with characteristic abnormalities in cerebrospinal fluid (CSF). Thus, in addition to magnetic resonance imaging, CSF examination is a central diagnostic procedure in patients with MS, which can corroborate a diagnosis of MS and may also help to discern differential diagnoses. The most important CSF finding in MS is the detection of persistent polyspecific intrathecal immunoglobulin synthesis. This review summarizes CSF findings of patients with MS and addresses issues of relevance for clinical practice, potential diagnostic pitfalls as well as new developments in CSF diagnostics of MS.

Free kappa light chains in cerebrospinal fluid as a biomarker to assess risk conversion to multiple sclerosis

Background

Multiple sclerosis (MS) initiates with a first attack or clinically isolated syndrome (CIS). The importance of an early treatment in MS leads to the search, as soon as possible, for novel biomarkers which can predict conversion from CIS to MS.

Objective

The purpose of this study was to assess the predictive value of the kappa index (κ index), using kappa free light light chains (κFLCs) in cerebrospinal fluid (CSF), for the conversion of CIS patients to MS, and compare its accuracy with other parameters used in clinical practice.

Methods

FLC levels were analysed in CSF from 176 patients: 70 as control group, 77 CIS, and 29 relapsing–remitting MS. FLC levels were quantified by nephelometry.

Results

κ Index sensitivity and specificity (93.1%; 95.7%) was higher than those from the immunoglobulin G (IgG) index (75.9%; 94.3%), and lower than those from oligoclonal IgG bands (OCGBs) (96.5%; 98.6%). The optimal cut-off for κ index was 10.62. Most of the CIS patients with κ index >10.62 presented OCGBs, IgG index >0.56 and fulfilled magnetic resonance imaging (MRI) criteria.

Conclusion

CIS patients above κ index cut-off of 10.62 present 7.34-fold risk of conversion to MS than CIS below this value. The κ index correlated with positive OCGBs, IgG index above 0.56 and MRI criteria.

Diagnostic and Prognostic Value of the Cerebrospinal Fluid Concentration of Immunoglobulin Free Light Chains in Clinically Isolated Syndrome with Conversion to Multiple Sclerosis

Background and objective

In this study, we evaluated the diagnostic and prognostic significance of cerebrospinal fluid free light chains (CSF FLC) at the time of clinically isolated syndrome (CIS).

Methods

We compared FLC-parameters at the moment of CIS in patients with conversion to multiple sclerosis (MS) after 2 years (CIS-MS), patients who remained stable both clinically and radiologically after 2 years (CIS-nonMS), patients with non-inflammatory neurologic diseases (NIND) as a comparison group and patients with other inflammatory neurologic diseases (IND) with intrathecal oligoclonal bands (OCB) synthesis. ROC-analysis was conducted to define FLC-assay characteristics and cut-off values. We also compared FLC-concentrations in CIS patients to determine their OCB-status. A correlation analysis was performed between FLC-concentrations and the expanded disability scale score (EDSS), annualized relapse rate (ARR) and MRI-activity (i.e., number of new and gadolinium-enhancing (Gd+) lesions) in patients.

Results

The levels of kappa-FLC (k-FLC_CSF) and lambda-FLC (λ-FLC_CSF) as well as kappa- and lambda-quotients (Q-k and Q-λ) were elevated in CIS-MS compared to the CIS-nonMS and NIND groups. These levels did not differ significantly when compared with the IND group. We identified several patients with high k-FLC_CSF and λ-FLC_CSF in OCB-negative CIS and IND groups. The level of k-FLC_CSF production was significantly higher in OCB-positive patients in the CIS-MS group compared to the CIS-nonMS group. The concentrations of k-FLC_CSF and Q-k in the CIS-MS group showed significant correlation with the level of EDSS after 2 years (k-FLC: r = 0.4477,p = 0.0016; Q-k: r = 0.4621, p = 0.0016). λ-FLC_CSF and Q-λ inversely correlated with the number of Gd+ lesions (CSF λ-FLC: r = -0.3698, p = 0.0223; Q-λ: r = -0.4527, p = 0.0056).

Conclusion

The concentration of CSF FLC predicts conversion to MS within 2 years following CIS. OCB-positive patients with an early conversion have a higher concentration of CSF-FLC. We have also shown a prognostic significance of k-FLC_CSF for future EDSS-progression.

Update on clinically isolated syndrome

Optic neuritis, myelitis and brainstem syndrome accompanied by a symptomatic MRI T2 or FLAIR hyperintensity and T1 hypointensity are highly suggestive of multiple sclerosis (MS) in young adults. They are called "clinically isolated syndrome" (CIS) and correspond to the typical first multiple sclerosis (MS) episode, especially when associated with other asymptomatic demyelinating lesions, without clinical, radiological and immunological sign of differential diagnosis. After a CIS, the delay of apparition of a relapse, which corresponds to the conversion to clinically definite MS (CDMS), varies from several months to more than 10 years (10-15% of cases, generally called benign RRMS). This delay is generally associated with the number and location of demyelinating lesions of the brain and spinal cord and the results of CSF analysis. Several studies comparing different MRI criteria for dissemination in space and dissemination in time of demyelinating lesions, two hallmarks of MS, provided enough substantial data to update diagnostic criteria for MS after a CIS. In the last revision of the McDonald's criteria in 2010, diagnostic criteria were simplified and now the diagnosis can be made by a single initial scan that proves the presence of active asymptomatic lesions (with gadolinium enhancement) and of unenhanced lesions. However, time to conversion remains highly unpredictable for a given patient and CIS can remain isolated, especially for idiopathic unilateral optic neuritis or myelitis. Univariate analyses of clinical, radiological, biological or electrophysiological characteristics of CIS patients in small series identified numerous risk factors of rapid conversion to MS. However, large series of CIS patients analyzing several characteristics of CIS patients and the influence of disease modifying therapies brought important information about the risk of CDMS or RRMS over up to 20 years of follow-up. They confirmed the importance of the initial MRI pattern of demyelinating lesions and of CSF oligoclonal bands. Available treatments of MS (immunomodulators or immunosuppressants) have also shown unequivocal efficacy to slow the conversion to RRMS after a CIS, but they could be unnecessary for patients with benign RRMS. Beyond diagnostic criteria, knowledge of established and potential risk factors of conversion to MS and of disability progression is essential for CIS patients' follow-up and initiation of disease modifying therapies.