Proximally evoked soleus H reflexes in the evaluation of axonal neuropathy

It is sometimes difficult to differentiate physiologically distal axonopathy from proximal root or nerve disease. Standard soleus H reflexes evoked by distal tibial nerve stimulation at the popliteal fossa are often absent in both syndromes. In this study we distinguish the two by the presence or absence of soleus H reflexes evoked by proximal sciatic nerve stimulation at the gluteal fold. In 12 normal subjects maximum H reflex amplitudes evoked by distal tibial and proximal sciatic stimulation were essentially equal. In 12 patients with suspected distal polyneuropathy, proximal but not distal stimulation evoked H reflexes. By contrast, in 10 patients with lumbosacral root or proximal nerve disease, both proximal and distal stimulation failed to elicit H reflexes. In 2 patients with lower motor neuronopathy, low but comparable amplitude H reflexes were evoked at both sites. We conclude that the presence of a proximally evoked soleus H reflex may provide specific evidence of distal axonopathy when standard soleus H reflexes are absent.