Sudomotor Function Testing: The Science, Clinical Applications, and Prospects for Preventive, Diagnostic, and Clinical Care

Sudomotor dysfunction is a common finding, and one of the earliest detectable abnormalities, in a number of peripheral and autonomic neuropathies. However, clinicians can attest to the ongoing difficulty in diagnosing dysautonomia without the proper tools. Sudomotor function testing (SFT) as assessed with Quantitative Sudomotor Assessment Reflex Test (QSART) correlates well with Intraepidermal Nerve Fiber Density (IENFD) from skin biopsies, which is considered one of the most objective quantitative measures of peripheral neuropathy. Similarly, Sweat Gland Nerve Fiber Density (SGNFD) correlates with scores used to assess peripheral neuropathy such as Neuropathy Impairment Score in the Lower Limb (NIS-LL) and Michigan Neuropathy Screening Instrument (MNSI). Sweat gland sympathetic nerve fibers are an integral part of the Autonomic Nervous System (ANS), a system in which the predominant dysfunction observed is Cardiac Autonomic Neuropathy (CAN) — this condition is recognized as a serious complication of diabetes, with a prevalence from 2.5 to 50% in patients with this disease. CAN persists in being an implication of the cause for an approximately 5-fold risk of mortality in such patients. Today, standardized implementation of cardiac autonomic reflex tests is used to identify peripheral and autonomic neuropathies. While these assessments are non-invasive and safe to perform, they have certain limitations. These assessments are influenced by caffeine, tobacco and exercise, a fact which must be taken into account when interpreting the results. Current methodologies for sudomotor function testing, i.e., QSART, Thermal Sensory Testing (TST) and Sympathetic Skin Response (SSR) used in standard practice remain underutilized. They cannot generally be performed in routine clinical setting and may not be fully sensitive for diagnosing the particularities of autonomic dysfunction diseases. Compared to these “gold standards,” SUDOSCAN, an FDA-cleared device, proves to be an excellent and reliable method to assess sudomotor function testing. SUDOSCAN is accessible, non-invasive, requires less than 3 minutes to conduct from start to finish, provides immediate results and requires no patient preparation. It has the ability to detect early onset abnormalities and evaluate treatment efficacy of chronic diseases. Utilizing SUDOSCAN as a clinical diagnostic tool allows dysautonomia to be better identified and treated in today’s clinical practice. Introduction Abnormalities in sudomotor function in diabetic patients were clinically measurable as early as the 1980s and were noted to correlate with the presence of autonomic neuropathy. The various techniques of sudomotor function testing (SFT), although each has its strengths and weaknesses, are very sensitive and specific in the detection of distal small fiber neuropathy. SFT, however, has remained underutilized in clinical practice, due to lack of