Define population based characteristics and disability progression among patients with objective evidence of small fiber neuropathy.

Small fiber neuropathy is a common referral to neurology practices. Lacking are uniform diagnostic criteria, consensus definitions, and an understanding of the natural history making anticipatory guidance difficult.

This is a retrospective chart review (1998-2017).  An electronic record retrieval system identified adult patients diagnosed with painful small fiber neuropathy residing in Olmsted or adjoining counties.  All patients had to have completed an EMG and have one objective small fiber test abnormality by quantitative sudomotor reflex screen (QSART), thermoregulatory sweat test (TST), quantitative sensory testing (QST), intraepidermal nerve fiber skin biopsy. Disability and impairment status decline was calculated against baseline with a questionnaire including daily living skills and serial neurological exams for neuropathy impairment score (NIS).

Inclusion criteria were met in 104 patients. The mean onset age was 54 years (14-83), 66% female. Sensory symptoms included burning 53%, numbness 58%, pain 78%, paresthesias 68%. EMG and clinical evidence for associated large fiber nerve involvement were common 42%.  Pain medications included opioids 25% and other 62%. Lower extremity onset was typical (76%). Objective testing abnormalities included QSART=36 (59%), TST=65 (89%), QST=17 (68%), skin biopsies=5 (71%). Of those surveyed, 8% self-reported becoming disabled over the study period. The median NIS was 6 (0-65) with a median change of 2 points (0-54) over median 3.8 years (0-15). Two patients (2%) had amyloid (1 hATTR, 1 AL), accounting for the largest cohorts change in NIS. Chart diagnosis included polygenic-idiopathic 77%, diabetes 9%, inflammatory 8%, MGUS 3%.

Among most patients with objective evidence of small fiber neuropathy, progression to self-reported disability is out of proportion to the objective worsening of neurological impairments. Rapid change may suggest amyloidosis. Additional studies are needed to understand if comorbidities may contribute to these observations.