Cramps, spasms and muscle stiffness.

Cramp syndromes pose a challenge for neuroscientists. The motor disorders of Isaacs syndrome have been ascribed to peripheral neuropathy, and sometimes there is ample supporting evidence of neuropathy. However, signs of overt neuropathy are found in a minority of cases and the essential findings (carpal and pedal spasm, pseudomyotonia and myokymia) may arise from abnormal excitability of the perikaryon because similar manifestations are seen in tetany and multiple sclerosis. The Moersch-Woltman (stiffman) syndrome differs from Isaacs' syndrome in essential characteristics. Hyperventilation syndromes may mimic either simple cramps, the Isaacs syndrome, the Moersch-Woltman syndrome, or the Foley and Denny-Brown syndrome of benign fasciculation and cramps. New approaches are needed to define the etiology and pathogenesis of these neurogenic disorders because the results of peripheral nerve block and spinal anesthesia have not been consistent in cases of typical Isaacs syndrome. Occupational cramps can be regarded as a form of action dystonia but that statement is a clue, not an "explanation". Myopathic disorders are only rarely a cause of cramp syndromes. In the glycogen storage disorders, the chemical basis of the cramp is still unproven. Whether myoadenylate deaminase is a cause of cramps is debated.