Muscle cramps in cancer patients.

We prospectively evaluated 50 cancer patients with new complaints of muscle cramps. Neurologic examination and laboratory evaluation identified disorders related to neural, muscular, or biochemical abnormalities in 41 (82%) patients. Abnormalities were confined mainly to the peripheral nervous system and included peripheral neuropathy in 22 patients, root and plexus pathology in 17 patients (six with leptomeningeal metastases), and polymyositis in two patients. Hypomagnesemia accounted for muscle cramps in only one patient. Identifiable causes of muscle cramps were related mostly either to metastatic or nonmetastatic complications of the underlying malignancy (14 patients) or to complications of its treatment (21 patients). Cramps, or rather complaints of cramps, were the presenting symptom of recognizable and previously unsuspected neurologic dysfunction in 64% (27 of 42) of the identified causes. Therefore, we conclude that muscle cramps in cancer patients may not be a benign complaint and that they usually mark the presence of an identifiable neurologic disorder. The use of simple clinical and laboratory measures is rewarding in the evaluation of these patients and leads to diagnosis in the majority of them.