Nonregional small fibre neuropathy in cases of autoimmune autonomic neuropathy

OBJECTIVE: Autonomic small fibre neuropathy is described in patients with autoimmune autonomic neuropathy (AAN). Few data are available on somatosensory function and skin biopsies in AAN. METHODS: Retrospective analysis of 17 patients (51.2 ± 6.8 years, n = 7 males) with AAN, including autoantibodies, quantitative sensory testing (QST, n = 13) and intraepithelial nerve fibre density (IENFD) in skin biopsy (n = 16). QST was performed according to the DFNS protocol over hands and feet dorsum. QST data were compared to healthy controls. Comparison of antibody-positive and antibody-negative cases. RESULTS: 70.6% of patients were antibody positive. 82.4% described at least one episode with sensory symptoms. Skin biopsies revealed reduced IENFD in 58.8% of patients, whereas neuropathic pain was only present in 41.2%. QST showed a nonregional increase for nonpainful thermal and mechanical detection rather than for mechanical pain thresholds. Compared to healthy controls, sensory loss for cold and warm detection thresholds and for the thermal sensory limen—the temperature difference between alternating warm and cold stimuli—was found on hands and feet (all p < 0.05). For nonpainful mechanical stimuli, the vibration detection threshold on the hand was increased (p < 0.05). Of all pain thresholds, only the mechanical pain threshold was elevated for pinprick stimuli to the feet (p < 0.05). INTERPRETATION: Findings are consistent with a sensory small fibre more than large fibre neuropathy in AAN. Sensory loss was comparably distributed across hands and feet, indicating that nerve fibre dysfunction was rather generalized. Serostatus was not a significant predictor of the small fibre deficit present in AAN.