Reduced reciprocal inhibition is seen only in spastic limbs in patients with neurolathyrism.

If reduced reciprocal inhibition plays a causal role in the pathophysiology of spasticity as has been suggested in several studies, the inhibition is expected to be impaired in spastic, but not in normal muscles. Patients with neurolathyrism offer a possibility of testing this prediction since the spastic symptoms in these patients are restricted to the lower extremities only. Three patients with neurolathyrism were tested. Their data were compared with 15 age-matched healthy subjects. All patients showed signs of spasticity in the legs. Two patients had normal voluntary muscle force in the lower extremities and one had decreased force. No clinical abnormalities were found in the upper extremities. Reciprocal inhibition between ankle dorsiflexor and plantarflexor muscles was absent in all patients, whereas the inhibition between wrist extensor and flexor muscles was present and of normal size and latency. These findings are consistent with the hypothesis that reduced reciprocal inhibition plays a causal role in the pathophysiology of spasticity.