Specificity of needle electromyography for lumbar radiculopathy and plexopathy in 55- to 79-year-old asymptomatic subjects.

Abstract

Determine specificity of needle electromyography for lumbar radiculopathy and plexopathy using a blinded study design. Asymptomatic community volunteers ages 55 and older, as part of a spinal stenosis study, were given a standardized electrodiagnostic evaluation by a blinded electromyographer. A monopolar needle was used to evaluate five leg muscles and the lumbar paraspinal muscles. The specificities of different diagnostic criteria for radiculopathy and plexopathy were then calculated. There were 30 subjects with a mean age of 65.4 yrs (SD 8.0). When only positive sharp waves or fibrillations were counted as abnormal, most of the diagnostic criteria (two limb muscles plus associated lumbar paraspinal muscle abnormal, two limb muscles abnormal, or one limb muscle plus associated lumbar paraspinal muscle abnormal) had 100% specificity. When we also included at least 30% polyphasia in the limb muscles as abnormal, the respective specificities were 97, 90, and 87%. When we also included at least 20% polyphasia in the limb muscles as abnormal, the respective specificities were 77, 60, and 60%. The specificity for plexopathy was 100% when only positive sharp waves or fibrillations were used, and it remained 100% when increased polyphasia was added. Needle electromyography has excellent specificity for lumbosacral radiculopathy and plexopathy when appropriate diagnostic criteria are used.