Reciprocal inhibition in patients with hand cramps.

We studied inhibition of median nerve H-reflex produced by radial nerve stimulation in both arms of 14 patients with hand cramps and 15 normal volunteers. Median nerve stimulation was delivered 1 and 0.5 msec before and 0, 0.5, 1, 2, 10, 20, 30, 50, 75, 100, 200, 500, and 1,000 msec after radial nerve stimulation. Recordings were from surface electrodes positioned over flexor carpi radialis. We identified three periods of attenuation of median nerve H-reflex amplitude in the control group. When radial nerve conditioning stimuli were delivered simultaneously, 10 and 75 msec before median nerve test stimuli, H-reflex amplitude diminished to 47%, 61%, and 69%. In the patient group we also found three periods of attenuation at the same delays, but the amount of attenuation was significantly less than in controls. Dividing the patients into two groups, dystonic hand cramp and simple hand cramp, both showed less inhibition than the control group, but the abnormality was greater in the dystonic cramp group. This test is the first to demonstrate physiologic disturbance in patients with hand cramps.