To evaluate the frequency and distribution of sudomotor abnormalities in individuals who presented to the autonomic laboratory and, subsequently, received a diagnosis of postural tachycardia syndrome (POTS).

Neuropathic POTS is one of several physiologically defined subtypes and has been investigated using quantitative sudomotor axon reflex testing (QSART), skin biopsy for intra-epidermal nerve fiber density (IENFD), quantitative sensory testing (QST), autonomic testing, and other investigative methods. Sympathetic neuronal denervation, leading to excessive venous pooling and reflex tachycardia, has been hypothesized as a key contributor to POTS. Sudomotor abnormalities have been reported in 38-75% of POTS patients, though sample sizes were small and/or relatively selected (6-152 subjects).

The University of Utah Autonomic Physiology Laboratory database was used to retrospectively investigate the proportion of patients with quantifiable sudomotor dysfunction as measured by > 1 abnormal sudomotor sites on QSART testing during standardized autonomic reflex screening, based on a cutoff of <5^th-percentile for sex (Sletten et al. 2015). This study was IRB approved, and consent waiver obtained. Inclusion criteria: laboratory diagnosis of POTS, confirmed by 10-minute head-up tilt table; age > 20. Exclusion: sudomotor medication effect; missing data.

374 patients, aged 20-65 were analyzed (2/2015-3/2022); 86% female. Of these, 79 (21%) had > 1 abnormal QSART site: 27 (34%) foot, 27 (34%) distal leg, 33 (42%) proximal leg, 29 (37%) forearm. The composite autonomic severity score (CASS) was > 1 in 243 (65%).

Our findings suggest that peripheral sudomotor impairment may be present in a lower proportion of POTS patients than previously reported. However, CASS was > 1 in over half of subjects. Studies using multimodal assessment to categorize neuropathic POTS tended to support a higher percentage of POTS subjects with neuropathic features, suggesting that QSART alone may be insufficient to detect neuropathic POTS.