A Study of H reflex in amyotrophic lateral sclerosis.

In amyotrophic lateral sclerosis (ALS), both anterior horn cell and corticospinal tracts are affected. H reflex studies were performed in 15 patients to study motor neuron excitability and to correlate the changes with the clinical signs. Soleus H reflex was unrecordable in two patients. In the remaining patients, there was lack of vibratory inhibition and reciprocal inhibition which was consistent with pronounced presynaptic and supraspinal influences respectively. High HM ratio was consistent with increased motor neuron excitability. Significant reduction of maximum M response in our patients was consistent with fall out of anterior horn cells. HM ratio, vibratory inhibition and reciprocal inhibition were not related with power, spasticity, clonus or extensor plantar response, which could be due to asymmetric focal neuronopathy.