L5 radiculopathy with reduced superficial peroneal sensory responses: intraspinal and extraspinal causes.

Thirteen patients were retrospectively identified with the electrodiagnostic pattern of combined L5 radiculopathy by needle electrode examination, and abnormality of the superficial peroneal nerve (SPN) sensory nerve action potential (SNAP) amplitude. To have combined L5-derived sensory and motor axon loss, lesions must be localized at or distal to the L5 dorsal root ganglion (DRG), but also proximal to the sacral plexus. Six patients had evidence of an active intraspinal canal (ISC) lesion, 3 had diabetes, and 4 had nonspecific causes. The ISC localization in at least 6 of our cases is counter to the commonly held electrodiagnostic dogma that L5 radiculopathy spares the SPN SNAP, but recent anatomic studies confirm the ISC location of up to 40% of L5 DRG. Thus loss of the SPN SNAP does not exclude ISC lesions.