Oligoclonal M bands unveils occult inflammation in multiple sclerosis

Introduction: Recent works demonstrate that patients with multiple sclerosis (pwMS) and oligoclonal M bands (OCMB) in cerebrospinal fluid (CSF) are at higher risk of conversion to secondary progressive course, suggesting a distinct pathophysiology pathway in these patients. Objectives: To analyze the relationship of serum neurofilament light chain (s-NFL) in absence of inflammatory activity in people with multiple sclerosis (pwMS) according to the presence of OCMB versus healthy controls (HC), and the effect of aging. Methods: Two cohorts of HC were compared to a cohort of pwMS without clinical or radiological signs of acute inflammation. Lack of inflammation was defined as the absence of relapses or gadolinium-enhancing lesions (GEL) brain in an MRI performed within three months before and after s-NFL determination. S-NFL was measured with SIMOa technology. OCMB in the cerebrospinal fluid (CSF) were analyzed with isoelectric focusing and immunoblotting. Results: 254 people were studied: 124 healthy voluntary controls and 130 pwMS. Despite the absence of inflammatory activity, pwMS and OCMB showed higher levels of s-NFL compared to those without OCMB and HC (11.4 pg/mL, 8.9 pg/mL and 9.0 pg/mL, respectively). A positive and exponential correlation between age and s-NFL was observed, with highest increases among pwMS and OCMB in the CSF. Discussion: In absence of overt inflammatory activity, pwMS and OCMB exhibit higher s-NFL levels, and a greater age-related increase. Thus, OCMB may portray an underlying inflammatory process not detected by conventional MRI studies and may explain the poorer prognosis of these patients.