Plasma neurofilament light chain is associated with clinical instability in chronic autoimmune neuropathies.

Neurofilament light chain (NfL) is a sensitive biomarker of axonal damage, but its clinical relevance in chronic autoimmune neuropathies remains incompletely defined. This study evaluated plasma NfL levels in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and multifocal motor neuropathy (MMN), compared with hereditary neuropathy (Charcot–Marie–Tooth disease type 1 A, CMT1A) and healthy controls, focusing on disease activity rather than diagnostic discrimination. Plasma NfL concentrations were measured using single molecule array (Simoa) technology in 41 patients (CIDP n = 16, MMN n = 7, CMT1A n = 18) and 25 age- and sex-matched controls. Disease severity was assessed using the Inflammatory Rasch-built Overall Disability Scale for autoimmune neuropathies and the Charcot–Marie–Tooth Neuropathy Score version 2 for CMT. Plasma NfL levels were significantly higher in patients with autoimmune neuropathies and CMT compared with controls. No significant differences were observed between inflammatory and hereditary neuropathies, and NfL levels did not correlate with disability scores. However, patients with autoimmune neuropathies and an unstable disease course, defined by more than two relapses, exhibited significantly higher plasma NfL levels. Across all groups, NfL concentrations showed a strong correlation with age. These findings suggest that while plasma NfL lacks diagnostic specificity among chronic neuropathies, it may be associated with disease instability in autoimmune neuropathies.