The role of somatosensory evoked potentials in the diagnosis of lumbosacral radiculopathies.

Electrophysiologic studies have an important role in the diagnosis of lumbosacral radiculopathies. Electrophysiologic methods which are used conventionally are needle electromyography (EMG), late responses (F wave and H reflex), and nerve conduction studies. Somatosensory evoked potentials (SEPs) are also important complementary diagnostic methods in the electrophysiologic evaluation of lumbosacral radiculopathies. In this study, we aimed to determine whether SEPs have an advantage over the conventional electrophysiologic methods or whether sensory nerve stimulated SEPs over mixed nerve stimulated ones or the lumbar recordings over the scalp recordings in diagnosing lumbosacral radiculopathies. For this reason, the study included 20 patients with unilateral and unilevel S1 radiculopathy due to intervertebral disc herniation confirmed by clinical examination and magnetic resonance imaging (MRI) as the patient group. And a control group of 18 healthy subjects were also included in the study. Nerve conduction studies, late responses and scalp and lumbar-recorded SEPs after sural and posterior tibial nerve stimulation were studied in both groups, while needle EMG was performed only in the patient group. Patients who manifested abnormal findings on needle EMG or on late responses also showed abnormal findings on at least one type of the SEPs. SEPs detected abnormalities in 5 patients (25%) in whom needle EMG or late responses did not suggest any abnormality. In this study we concluded that SEPs may provide diagnostic information beyond conventional electrodiagnostic methods and that lumbar-recorded SEPs may have an advantage over scalp-recorded ones and sensory nerve stimulated SEPs over mixed nerve stimulated ones.