Summary Of Evidence

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Analysis of Evidence

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Abstract:
Short-latency somatosensory evoked potentials (SEPs) represent electrophysiologic responses of the somatosensory pathways to stimulation. Somatosensory testing involves the application of a series of brief electrical stimuli over peripheral nerves (e.g., the median, peroneal, and tibial nerves) and recording the resulting evoked potentials over proximal portions of the nerves and central pathways which were stimulated, the plexus, spine and/or scalp. Action potentials recorded from these sites are averaged by a computer to improve signal clarity and then displayed in standard formats on the computer’s screen as well as in printed form.

A provider trained in interpreting clinical evoked potential studies analyzes the waveforms. The waveforms obtained should be described by nerve being stimulated, the recording sites, peak latencies, interpeak intervals (when appropriate), and amplitudes of the significant components. The nerves most commonly stimulated are the median nerve at the wrist for testing in the upper extremity, and the posterior tibial nerve at the ankle or common peroneal nerve (CPN) at the knee for the lower extremity.

SEPs evaluate the entire somatosensory pathway from the site of stimulation up to the cerebral cortex. It is possible to distinguish between lesions located in the peripheral nerve, in the dorsal column spinal cord pathway, or higher centers in the brain up through the cortex. In general, there is no need for SEP in the diagnosis of most peripheral neuropathies because the conventional nerve conduction studies or needle EMG can identify these types of lesions and no added information is obtained from SEP. This local coverage determination discusses medically necessary indications and limitations for SEPs.

Indications:
Medicare will consider the use of short-latency somatosensory evoked potentials to be medically reasonable and necessary to assist in the diagnosis of certain neuropathologic states (as described below) to provide information for treatment decisions and for intraoperative electrophysiological monitoring during spinal surgeries in which there is risk of additional nerve or spinal cord injury. However, it is not anticipated that such monitoring will be medically necessary for the typical cervical or lumbar root decompression procedures.

SEPs are used to evaluate the more proximal segments of nerves and the integrity of the central somatosensory pathways when abnormality of conduction through the brain and/or brainstem, spinal cord, and/or peripheral nerves is suspected. This utilization would include conditions such as multiple sclerosis, cervical spondylosis with myelopathy, coma, spinal cord trauma, myoclonus, Friedreich’s ataxia, syringomyelia, spinal cord tumors, spinal stenosis and other conditions where there is spinal cord compression.

Limitations:
SEP studies are appropriate only when a detailed clinical history and neurologic examination and appropriate diagnostic tests such as imaging studies, electromyogram, and nerve conduction studies make a lesion (or lesions) of the central somatosensory pathways a likely and reasonable differential diagnostic possibility.