Objectives: To examine the results of thermoregulatory sweat testing in patients with erythromelalgia and to compare them with the results of other neurophysiologic tests of small-fiber nerve function. Design: Retrospective study. Setting: Tertiary referral center. Patients: Thirty-two consecutive patients with erythromelalgia who had thermoregulatory sweat testing in addition to vascular and nerve testing. Intervention: The following information was abstracted for each patient: demographics, clinical presentation, and results of thermoregulatory sweat testing, vascular (noninvasive) testing, and nerve testing (electromyography and autonomic reflex screen, including quantitative sudomotor axon reflex test). Main Outcome Measures: Results of thermoregulatory sweat testing to evaluate small-fiber neuropathy, compared with other tools used to estimate small-fiber neuropathy. Results: Thermoregulatory sweat testing results were abnormal in 28 (88%) of 32 patients, and quantitative sudomotor axon reflex test results were abnormal in 22 patients (69%). Abnormalities noted on thermoregulatory sweat testing varied from local hypohidrosis or anhidrosis to global anhidrosis. Global or almost-global anhidrosis was present in 8 patients (25%); in 19 patients (59%) the anhidrosis was distal, and 1 other patient (3%) had a less specific pattern of anhidrosis (multifocal or regional). The area of anhidrosis generally corresponded to the area that was symptomatic of the erythromelalgia. Conclusions: Small-fiber neuropathy is prevalent in most patients with erythromelalgia. Thermoregulatory sweat testing is a sensitive and useful marker of small-fiber neuropathy in these patients.
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