The dynamic sweat test in patients with pure autonomic failure: a pilot study

<h3>Introduction</h3> The dynamic sweat test (DST) is an established tool for the evaluation of sudomotor function. We aimed to characterise the sudomotor pattern of patients with pure autonomic failure (PAF) with the DST, and to evaluate its usefulness in distinguishing patients with phenoconversion to overt parkinsonism. <h3>Methods</h3> As part of the QSA-PRODROMAL study, consecutive patients with an initial PAF diagnosis were included. Diagnoses were revised at follow up. Number of activated sweat glands, mean gland sweat production, and total sweat of a 1cm2 area of upper and lower limbs were investigated. Data were analysed using non-parametric tests, presented as median and interquartile ranges. <h3>Results</h3> 34 patients (11F, age 62[57–71] years) with initial PAF were included. 7 patients phenoconverted (4MSA-P, 2DLB, and 1PD), while 27 retained a PAF phenotype. There was a trend in reduction of total sweat production, both for upper (PAF 213.99[99.07–406.57], non- PAF 415.92[120.72–552.53] nL/cm2/min, p=0.641) and lower (PAF 47.63[23.39–140.43], non- PAF 116.16[60.35–181.58] nL/cm2/min, p=0.066) limbs. <h3>Conclusion</h3> Postganglionic total sweat production might be lower in patients with predominantly peripheral autonomic involvement (PAF) compared to the widespread alpha- synucleinopathies. DST may aid in distinguishing different phenotypes, but future studies and wider samples are needed to confirm the role of such technique.