Electromyography in musculoskeletal pain: A reappraisal and practical considerations

Patients with musculoskeletal pain (MSP) and local tenderness in the back and extremities are frequently referred to electromyography (EMG) laboratory to assess the integrity of the spinal nerve roots, peripheral nerves, and skeletal muscles. When focal muscle weakness and anatomical sensory deficits are clinically evident, this procedure is almost always abnormal. In some situations, when the presenting symptoms consist of local pain and tenderness without neuromuscular deficits, its diagnostic utility becomes questionable as illustrated in the present study.

EMG findings of 75 patients referred for evaluation of local MSP and tenderness in the neck and lower back and in the upper and lower extremities were reviewed. These patients were selected from a group of 200 patients referred for evaluation of unilateral local pain and tenderness in various parts of the body. All EMG procedures and clinical neurologic examination were performed by the author and all underwent magnetic resonance imaging of the affected parts of the body prior to the procedure. None of the 75 patients studied had concurrent medical disorders or had previous spinal root injuries or surgeries to the spine.

All 75 patients in this study showed normal EMG of the affected extremities and normal peripheral nerve conduction study. Those with herniated disc in the cervical or lumbar spine presenting with local pain and tenderness in the neck and lower back but without neurologic deficits or clear radicular symptoms, had normal study also. The remaining 125 patients excluded from the study, had various EMG and peripheral nerve abnormalities that can be attributed to concurrent medical disorders and previous injuries to the spinal roots.

Use of EMG in the diagnosis of local MSP, unless associated with clinical neurologic deficits, almost always yields negative results. The utility of this procedure is limited to pathology in the motor unit. It cannot assess the function of the sensory components of the spinal roots, small-diameter sensory nerves, and the sensory innervation of the spine via sinuvertebral nerve. Therefore, if the motor unit is anatomically and physiologically intact, the procedure is of little value in the diagnosis of MSP. Likewise, peripheral nerve conduction study is likely to be normal unless clear neurologic deficits are present. The present study illustrates that a good history and meticulous neurologic examination should be an integral part of an ideal electrodiagnostic procedure.