**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.