Recruitment curve of the soleus H reflex in patients with neurogenic claudication.

The diagnosis of neurogenic claudication (NC) remains uncertain when no definite signs of radicular lesions are found in electrophysiological testing. However, the functional deficit could be demonstrated during the brief time in which the patients complain of pain and weakness in the muscles of the lower limbs after walking. We have used electrophysiological testing of the H reflex and the F wave to document the transient functional derangement expected to occur at the radicular level in patients with NC after walking. We examined the recruitment curve of the soleus H reflex, and the chronodispersion of the posterior tibial nerve F wave, at rest and after a walking exercise that triggered their symptoms in 10 patients with NC, with no positive electrophysiological findings of radicular lesion. The same studies were performed in 5 age-matched healthy volunteers, used as control subjects, who were asked to walk for 30 min. At rest before walking, no abnormalities were found in any of the patients. After walking, the H wave showed a transient increase in its threshold with respect to that of the M wave in 7 patients (70%). Such abnormality lasted for a mean period of 7 min. In 2 of these patients there was also an increase in the F-wave chronodispersion. Our data suggest that nerve conduction is transiently blocked in large myelinated fibers at a radicular level in patients with NC after walking. Partial interruption of the H-reflex circuit could be one of the pathophysiological mechanisms underlying NC.