Nerve Conduction Studies, Electromyography and Somatosensory Evoked Potentials: Part 2
Electrodiagnostic studies, including, nerve conduction studies (NCS), needle electromyography (EMG), and somatosensory evoked potential studies (SSEPs) should be considered an extension of the history and physical examination and not merely a substitute for a detailed neurologic and musculoskeletal examination.
These studies are helpful in the evaluation of patients with limb pain where the diagnosis remains unclear (e.g. perineal neuropathy versus a radiculopathy). They are also helpful in excluding other causes of sensory and motor disturbances, such as peripheral neuropathy and motor neuron disease. They can also provide useful prognostic information by quantifying the extent and acuity of axonal involvement in radiculopathies.
H-Reflex and F Waves
Performing late response such as the H-reflex can provide valuable information regarding the proximal nerve/nerve root involvement. The H-reflex is both a sensitive and specific marker for involvement of the S1 root. F waves, also used to detect abnormalities in the proximal portion of nerves, are too nonspecific to be clinically useful in the setting of radiculopathy. Electrodiagnostic testing is usually not necessary in a clear-cut radiculopathy or in patients with isolated mechanical low back symptoms. Furthermore, these studies do not assess the smaller myelinated and unmyelinated nerve fibers, which are typically responsible for pain transmission.
Somatosensory evoked potential studies are of limited value in the assessment of acute low back pain and radiculopathy. They are not indicated unless there are neurologic signs and symptoms suggestive of pathology, which would indicate involvement of the somatosensory pathways. Some have found dermatomal and motor evoked potentials helpful in the diagnosis of spinal stenosis, but these are not routinely employed in clinical practice.