Dorsal Root Ganglion Location and Superficial Peroneal Sensory Nerve Action Potential Response in L5 Radiculopathy

OBJECTIVE: To find the correlation between dorsal root ganglion location and abnormal superficial peroneal sensory nerve action potential (SNAP) response in L5 radiculopathy. METHOD: This retrospective study included thirty-three patients with unilateral L5 radiculopathy, who had no peripheral polyneuropathy, focal neuropathy or other metabolic disease and were under 60 years. 33 patients were classified to two groups: group I with an abnormal superficial peroneal SNAP response and group II with a normal superficial peroneal SNAP response. Using axial view of MRI, the location of dorsal root ganglion (DRG) of the study group was classified into intraspinal, intraforaminal and extraforaminal space. RESULTS: In group I, 71% of L4 dorsal root ganglion was located in intraforaminal space, and 14% in extraforaminal space and 64% of L5 DRG was in intraforaminal space and 14% in intraspinal. In Group II, 42% of L4 DRG was located in intraforaminal space, and 58% in extraforaminal and 26% of L5 DRG in intraforaminal space and 63% in extraforaminal space. Group I subjects were more located in the intraforaminal space than Group II subjects (p <0.05). CONCLUSION: In spite of belief that "radiculopathy involves the nerve root proximal to DRG", the significant proportion of dorsal root ganglion was located inside intraforaminal space. Thus the intraspinal lesion such as disc protrusion or spondylotic encroachment may compress DRG and cause abnormal findings of SNAP in EMG study.

Diagnostic Values of Tibialis Anterior H-reflex in the Single L5 Radiculopathy

OBJECTIVE: To evaluate the values of H-reflex from tibialis anterior in the diagnosis of L5 radiculopathy. METHOD: The subjects were 37 patients and 30 normal controls. The patient group was composed of 28 patients with L5 radiculopathy and 9 patients with S1 radiculopathy, which were confirmed by clinical, radiological, and electrodiagnostic studies. Tibialis anterior H-reflex (TA-H reflex) was recorded from maximally contracting tibialis anterior muscle by averaging technique and submaximal stimulation of common peroneal nerve. Sensitivities and specificities were delineated from the several diagnostic criteria. RESULTS: In the normal controls, mean side to side difference in the TA-H reflex latency was 0.66+/-0.48 msec and mean amplitude ratio was 75+/-16%. The diagnostic criteria of abnormal TA-H reflex were latency difference above 1.62 msec and amplitude ratio less than 42.2%. The abnormal TA-H reflexes were shown in 17 out of 28 patients with L5 radiculopathy and 1 out of 9 patients with S1 radiculopathy. Sensitivity and specificity of TA-H reflex as a diagnostic criteria of L5 radiculopathy were 61% and 89%, respectively. CONCLUSION: Tibialis anterior H-reflex might be useful in the diagnosis of L5 radiculopathy.