To describe the utility of thermoregulatory sweat testing (TST) in the diagnosis of sensory neuronopathies.

Sensory neuronopathies have been described in small and large fiber neuropathies. Patients present with variable and multifocal sensory loss. Diagnosis is challenging with many of the traditional testing modalities such as EMG/NCS, nerve or skin biopsy and autonomic testing being normal. There is little data regarding the diagnostic utility of TST.

We conducted a retrospective review of patients with a sensory neuronopathy and a TST who presented to the Mayo Clinic, Rochester between 2000 -2018, through database search algorithms. Patients were excluded if alternate causes for sweating abnormalities were found.

We identified 36 patients with sensory neuronopathy who had TST performed. Median age at diagnosis was 51 years (range 20-77) and 16 (44%) were male. The pattern of TST findings are as follows: 2 (6%) had global anhidrosis, 10 (28%) had regional changes, 11 (31%) had multifocal and/or patchy changes, 8 (22%) had distal changes, and 4 (11%) had a normal TST. One patient had hyperhidrosis. In our cohort, 10 (28%) patients had predominantly small fiber involvement, and 26 (72%) had predominantly large fiber involvement. Twenty-eight (78%) patients were presumed to have an inflammatory etiology for their presentation, with 8/28 patients having Sjogren’s associated neuronopathy and 2/28 patients having coeliac disease or related symptoms. All patients had EMG/NCS with 9 (25%) having a normal study. In the 27 (75%) patients with an abnormal EMG/NCS, the major finding was absent or low amplitude sensory nerve action potentials. Twelve patients had a nerve biopsy, with 10/12 having changes suggestive of inflammation.  

Sensory neuronopathies present a diagnostic challenge. Anhidrosis is a common manifestation of the large and small fiber neuropathic variants. The thermoregulatory sweat test is a valuable diagnostic tool with 89% of patients revealing abnormal results.