Autonomic evaluation is independent of somatic evaluation for small fiber neuropathy

The relationship between the autonomic reflex screening test (ARS) and measures of sensory function and structure (quantitative sensory testing (QST) and intraepidermal nerve fiber density (IENFD)) remains uncertain in patients with distal small fiber neuropathy (SFN). The aim of this study was to evaluate the correlations among a range of autonomic (quantitative sudomotor axon reflex test (QSART), cardiovagal and cardio adrenergic tests and the composite autonomic severity score (CASS)) and somatic sensory measures (QST of vibration, cooling and heat-pain thresholds and IENFD).

122 patients with clinically suspected sensory neuropathy without motor weakness and with normal nerve conduction studies underwent blinded autonomic reflex screening test (ARS), quantitative sensory testing (QST) and skin biopsy (IENFD) for diagnosis of SFN. The relationship between autonomic and somatic sensory measures was assessed.

There was no association between autonomic function measures (QSART volume, CASS_QSART, CASS_vagal, CASS_adrenergic or total CASS) and small fiber sensory measures (IENFD, cooling or heat-pain thresholds). Weak correlations were noted among some modalities of QST (vibration and cooling thresholds) and IENFD.

Autonomic and sensory outcomes are independent (complementary) measures of distal SFN, and should where feasible be used concurrently in the evaluation of SFN.