New Jersey Chiropractic Council on Neurology

The American Association of Electrodiagnostic Medicine references somatosensory evoked potentials and states that radiculopathies may be difficult to evaluate electrophysiologically.  F wave and needle EMG abnormalities, including those encountered in paraspinal muscles, reflect only dysfunction of the motor root.  H reflexes on the other hand, are limited to diseases affecting the S1 root only.  However, somatosensory evoked potentials, elicited by segmental sensory stimulation may provide valuable information in a disc disease involving common cervical and lumbar levels, with predominant sensory abnormalities.  A good correlation between the dermatomal somatosensory evoked potentials and myelographic and clinical abnormalities has been demonstrated.

AAEM, October 1993, page 3; The dermatomal somatosensory evoked potential is particularly helpful in conditions which produced isolated involvement of the sensory fibers at sites that are either proximal in the peripheral nervous system i.e. at the plexus and root levels or within the central neuraxis.  In this case, peripheral nerve conduction studies and EMG may not be capable of detecting the lesion, (for example as in a primary sensory fiber radiculopathy with preganglionic root compression), whereas the dermatomal somatosensory evoked potential is more likely to do so.

Needle EMG is useful for detecting motor weakness concomitant to radiculopathy that sometimes cannot be detected by nerve conduction study alone.  However, nerve conduction and somatosensory evoked potentials can detect sensory radiculopathies that cannot be detected by needle EMG.  There are clear disadvantages with needle EMG: it is an invasive, painful procedure and it cannot detect sensory radiculopathies.

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