Reciprocal inhibition in hemiplegia: correlation with clinical features and recovery

Previous reports have described changes in reciprocal Ia inhibition in hemiplegic patients, but correlations between the amount of Ia inhibition and the clinical deficits have not been well established.

We studied reciprocal inhibition between ankle flexors (tibialis anterior) and extensors (soleus) in 16 hemiplegic patients at various stages following a stroke and in 26 control subjects. The amount of disynaptic Ia inhibition was determined from the short latency suppression of the soleus or tibialis anterior H-reflexes by conditioning stimulation of the antagonistic muscle nerves.

Disynaptic Ia inhibition from peroneal nerve afferents to soleus motoneurones was increased in patients who showed good recovery of function with mild spasticity. However, it was not changed, or even sometimes diminished, in patients who made a poor recovery and had more marked extensor spasticity. In patients where serial recordings were obtained there was an increase in Ia inhibition during the recovery period following stroke. Ia inhibition to the tibialis anterior motoneurones tended to be greater in the poor recovery patients with marked spasticity than in the good recovery patients. The late (D1) inhibition, presumably due to presynaptic inhibition, was decreased in the patients, although consistent correlations between the amount of this inhibition and the clinical features were not clearly demonstrated.

Changes in excitability of Ia inhibitory pathways can be correlated with some of the clinical features seen in hemiplegia. Increased Ia inhibition of soleus motoneurones during recovery may be a mechanism to compensate for loss of descending motor commands.