Abstract
Objective: This study aims to characterize: 1) sympathetic sudomotor fiber damage using the sweat gland nerve fiber density (SGNFD) and 2) to evaluate diagnostic accuracy of SGNFD using ENFD as a reference test in idiopathic and secondary SFN.
Background: Small fiber neuropathy (SFN) is common problem, affecting sensory and autonomic fibers, resulting in pain and dysautonomia. SFN is commonly diagnosed with skin biopsy for epidermal nerve fiber density (ENFD) which evaluates sensory fibers only.
Design/Methods: In a retrospective, 2 sites study of patients referred for evaluation of SFN, skin biopsies were obtained for assessment of SGNFD and ENFD. Idiopathic and secondary SFN was classified as sensory (abnormal ENFD), autonomic (abnormal SGNFD) and mixed (both ENFD and SGNFD abnormal).
Results: 1111 subjects (mean±sd) age=50.0±17.6, men/women=367/744, were analyzed. The most common diagnoses associated with secondary SFN were Parkinson disease (n=95) and diabetes (n=95). Idiopathic SFN (n=305) was classified as autonomic (n=117), sensory (109) and mixed (79). Among secondary SFN, the most common type was mixed SFN (n=37) in diabetes and autonomic SFN in PD (n=20). Sensitivity/specificity of SGNFD to predict ENFD was 50%/27%, ROC 0.67, p<0.0001. Adding SGNFD to ENFD increased the diagnostic yield of skin biopsy by 16.5 %.
Conclusions: Autonomic sudomotor fiber damage is common in SFN. SGNFD and ENFD are poor predictors of each other. Simultaneous utilization of SGNFD and ENFD improves the SFN diagnosis and enables classification of SFN (sensory/autonomic/mixed) which may increase understanding of SFN pathologies
Disclosure: Dr. Novak has nothing to disclose. Dr. Qin has nothing to disclose.
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