Proceedings of the 25th BCTRIMS Annual Meeting

Introduction: Multiple Sclerosis (MS) diagnostic criteria have evolved over time and continues to apply a combination of clinical, imaging, and laboratory findings. Although biomarkers of intrathecal cerebrospinal fluid (CSF) synthesis have been less emphasized in successive iterations to the McDonald criteria, it remains a valuable diagnostic test, especially in developing countries and specific populations (atypical findings, children, older patients and overlapping cerebrovascular disease). The last recommendation allows the positive CSF oligoclonal bands (OCBs) as an alternative to dissemination in time. The same last panel suggests that elevated immunoglobulin G (IgG) index should be interpreted with caution when testing for oligoclonal bands is negative or not done.

Objectives: To investigate whether IgG index can reliably predict OCBs findings in a Brazilian setting.

Methods: In this cross-sectional study, we analyzed persons with MS (PwMS) fulfilling the 2017 McDonald criteria, with available OCBs and IgG index results. The IgG index was considered elevated if ≥ 0.700. We calculated the positive predictive value (PPV), negative predictive value (NPV) and receiver-operating characteristic (ROC) area under curve with 95%, with confidence intervals (CIs).

Results: A total of 108 PwMS were analyzed, of which 81.5% were OCB positive and 72.5% showed an elevated IgG index. The IgG index value ≥0.7 showed a PPV of 94.9% (95% CI 87.4-98,6%) when OCBs are positive. The NPV of a normal IgG index was 44.8% (95% CI 26.4-64.3%) when OCBs are negative. The ROC area under curve was 0.817 (95% CI 0.693-0.940; p<0.001).

Conclusions: The high PPV for the presence of OCB can facilitate the MS diagnostic process in typical clinical and imaging situations, especially in developing countries with difficulty or delay in determining OCB (given the low cost and easy accessibility of the IgG index). However, a normal IgG index has a low capacity to predict negative OCB.