To identify active axonal damage by measurement of serum neurofilament light chain (sNfL) levels in patients with small fiber neuropathy (SFN) and ongoing neuropathy symptoms.

SFN is associated with sensory symptoms and is evident by skin biopsy which show a reduction of the intraepidermal nerve fiber density (IENFD) indicating skin denervation. SFN patients may complain of prolonged/worsening symptoms, but it is not clear if this is associated with continuous axonal damage.  

Blood samples were collected from 95 consecutive patients that were referred for a skin biopsy due to suspected SFN. All patients had symptoms that were consistent with a clinical diagnosis of SFN. Patients were excluded if they had clinical or imaging evidence for a central nervous system disorder, electrodiagnostic abnormalities or absence of electrodiagnostic evaluation. Following these exclusions, 34 patients were included for analysis. Skin biopsy was performed 2-3 months from symptoms onset by 4 patients, 4-12 months by 7, and after more than 12 months by 23. Severe skin denervation was defined by an intraepidermal nerve fiber density (IENFD) below the 5^th percentile per age, mild denervation when the IENFD was at the 5-20^th percentiles, and above the 20^th percentile was considered normal.