Small-fiber neuropathy with cardiac denervation in postural tachycardia syndrome

Postural tachycardia syndrome (POTS) is a disorder of orthostatic intolerance characterized by excessive tachycardia of unknown etiology. Our objective in this study was to evaluate the correlation between C-fiber involvement as shown by skin biopsy and adrenergic cardiac metaiodobenzylguanadine (MIBG) uptake in POTS patients. Skin biopsies of 84 patients with POTS were examined by Protein Gene Product 9.5 (PGP9.5) immunohistochemistry and were compared with MIBG myocardial scintigraphy imaging data. Mean intraepidermal nerve fiber (IENF) density was in the lower normal age-adjusted range, 7.2 ± 2.9/mm (normal ≥ 7/mm), and was slightly below the normal range in 45% of POTS patients. MIBG uptake was reduced in 21% of patients. Low IENF density correlated with reduced cardiac MIBG uptake (r = 0.39, P = 0.001). A subset of neuropathic POTS patients may harbor mild small fiber neuropathy with abnormalities of unmyelinated nerve fibers in the skin associated with reduced myocardial postganglionic sympathetic innervation.