Serum neurofilament light chain levels in patients with small-fiber neuropathy

BACKGROUND: Serum neurofilament light chain (sNfL) levels are an increasingly employed tool for the assessment of active axonal injury in a variety of neurological disorders including polyneuropathy. Injury to the small nerve fibers can lead to small fiber neuropathy (SFN), a neurological condition which is clinically manifested by combination of burning pain, various sensory disturbances and symptoms of autonomic dysfunction. SFN is evident by identifying reduced epidermal nerve fiber density (ENFD) in skin biopsy. OBJECTIVE: To assess the utility of sNfL measurement as a marker for active axonal injury in a population of patients who were referred for skin biopsy as part of the evaluation of chronic sensory symptoms. METHODS: sNfL levels were measured in 94 patients at the time of skin biopsy. Clinical, electrodiagnostic, and imaging data were collected and neurological comorbidities including central nervous system disorders, large-fiber polyneuropathy, and radiculopathy which may increase sNfL levels were reviewed. RESULTS: Eighty-six patients had pathological skin biopsy result supporting the diagnosis of SFN. sNfL was increased in 9 (10%) SFN patients. Seven of them had neurological comorbidities which may explain the elevated sNfL. The other two patients had history of hypothyroidism and endometriosis. CONCLUSIONS: sNfL levels are typically normal in patients with SFN. Furthermore, when sNfL are elevated, evaluation for another neurological disorder should be considered.