Small fibers involvement in Friedreich's ataxia.

Although the involvement of large myelinated sensory fibers in Friedreich's ataxia (FA) is well documented, an impairment of unmyelinated fibers has not been described. We demonstrate an involvement of cutaneous unmyelinated sensory and autonomic nerve fibers in FA patients. We performed a morphological and functional study of cutaneous nerve fibers in 14 FA patients and in a population of control subjects. We used immunohistochemical techniques and confocal microscopy applied to punch skin biopsies from thigh, distal leg, and fingertip, and compared the density of epidermal nerve fibers (ENFs) with the results of mechanical pain sensation and thermal and tactile thresholds performed on hand dorsum, thigh, distal leg, and foot dorsum. We observed in our patients a statistically significant loss of ENFs, a reduced innervation of sweat glands, arrector pilorum muscles and arterioles, and an impairment of thermal and tactile thresholds and mechanical pain detection.