Cramps and small-fiber neuropathy

Introduction: Muscle cramps are a common complaint and are thought to arise from spontaneous discharges of the motor nerve terminal. Polyneuropathy is often causative, but small-fiber neuropathy (SFN) has not been assessed. Methods: We performed skin biopsies on consecutive patients with cramps but without neuropathic complaints. Twelve patients were biopsied, 8 with normal small-fiber sensation. Results: Seven patients had decreased intraepidermal nerve fiber density (IENFD), 2 with non-length-dependent loss. A cause for neuropathy was found in 1 patient with cramp-fasciculation syndrome. Creatine kinase was elevated in 8 patients, 4 with decreased IENFD. Muscle biopsy, performed in 8 patients, but was diagnostic in only 1, with McArdle disease. Conclusions: Our data show that 60% of patients with muscle cramps who lack neuropathic complaints have SFN, as documented by decreased IENFD. Cramps may originate as local mediators of inflammation released by damaged small nerve that excite intramuscular nerves.