Patterns of H-reflex abnormality in patients with low back pain.

H-reflex was studied in 43 patients with low back pain (including 20 patients with neurological deficit corresponding to S1 radix and 23 patients without deficit) and 20 control subjects. Among patients with neurological deficit the abnormality consisted of absent H-reflex (7 patients), increased H-latency (3 patients), reduced H/M maximal amplitude ratio (5 patients) or a combination of the latter two (2 patients). The H/M ratio was significantly reduced in this group as compared to control subjects and between affected and unaffected sides. Abnormal H-reflex correlated well with ankle jerk hypo- or areflexia, S1 sensory deficit and lumbar myelographic/CT abnormality. In 23 patients without deficit, increased H-latency and/or reduced H/M ratio was observed in 4 cases. Enhanced H/M ratio was noted in only 2 patients of this group. Use of H/M ratio seems to increase the sensitivity of H-reflex in the diagnosis of S1 radiculopathy.