Reciprocal Ia inhibition in patients with asymmetric spinal spasticity

Previous studies on reciprocal Ia inhibition in spinal spasticity were contradictory, probably due to differences in the etiology, severity, and the course of recovery from the disease. The purpose of the present study was to establish a correlation between Ia inhibition and clinical abnormalities in spasticity following a spinal cord injury (SCI).

We studied reciprocal Ia inhibition in bilateral soleus muscles in five SCI patients with marked asymmetry of spasticity and functional recovery for the right and left legs. Reciprocal Ia inhibition was determined from the short latency suppression of the soleus H-reflex by conditioning stimulation of the peroneal nerve.

In all the patients, Ia inhibition was asymmetric. Ia inhibition in the legs with good recovery and less spasticity was pronounced, but Ia inhibition in the more spastic legs was small or absent. Facilitation was seen only on the sides with poor recovery in two patients. In the healthy subjects the amount of Ia inhibition varied, but no side-to-side difference was found.

These results suggest that reciprocal Ia inhibition varies according to the functional recovery. Pronounced Ia inhibition may be related to good functional recovery in patients with SCI.