Measurements of sudomotor function and pathology have shown to be useful in evaluating peripheral neuropathy. Ross Syndrome (RS), which is characterized by prominent sudomotor dysfunction, is known to be associated with cutaneous sensory and autonomic denervation. Axon reflex testing can be used to measure local post ganglionic sudomotor function. Coupled with high definition video, measures of axon reflex-stimulated sweat from individual sweat glands in situ can be correlated with histopathologic measurements.

Three patients with Ross Syndrome and three healthy control subjects underwent neurological exam and axon reflex sweat testing. Based on clinical history, exam, and results of sweat testing, skin biopsies were performed in sweating and non-sweating areas of the body in RS patients, and in matching areas in control subjects. Software was used to trace and measure SGs and encapsulated nerve fibers. Histologic measurements were correlated with physiologic measurements of sweating using both quantitative sudomotor axon reflex testing (Q-sweat) and video indirect sweat testing.

RS patients showed reduced density of activated sweat glands (SGs), reduced sweat rate per SG, and reduced total sweat and SG nerve fiber length (SGNFL) compared to controls, more reduced in affected areas. VIP+ fibers were markedly reduced in RS. SGNFL correlated best with total sweat within the 3mm punch biopsy area.  

Ross Syndrome is a rare but often overlooked condition which causes significant disability, characterized by prominent involvement of sudomotor nerves. Immune fluorescent confocal microscopy and video sweat testing offer the ability to characterize the pathology associated with RS, and to correlate histologic and functional data.