Combined recordings of compound nerve action potentials and spinal cord evoked potentials in differential diagnosis of spinal root lesions

Three cases are presented to demonstrate the diagnostic value of sensory neurography in combination with somatosensory evoked potentials in the diagnosis of proximally located neuropathy and its differentiation to centrally located demyelinating processes. Simultaneous recording of cortical and spinal evoked potentials, as well as peripheral nerve action potentials, revealed in two cases (herpes zoster, Guillain-Barré syndrome) a site of lesion at the spinal roots suggesting radiculitis and in one case (tick bite) a site of lesion central to the source of lumbar evoked potentials suggesting myelitis. In all cases almost complete recovery of sensory conduction velocities suggests a complete repair myelination not previously described.