Incremental ability of needle electromyography to detect radiculopathy in patients with radiating low back pain using different diagnostic criteria.

OBJECTIVE: To determine the incremental ability of different needle electromyography diagnostic criteria to detect lumbar radiculopathy.

DESIGN: Blinded cross-sectional study.

SETTING: University hospital.

PARTICIPANTS: Subjects aged 55 to 80 years with radiating low back pain (n=48; mean age ± SD, 67.9±7.3y) and who were asymptomatic (n=30; mean age ± SD, 65.4±8y).

INTERVENTIONS: Electrodiagnostic evaluation by a blinded electromyographer. A monopolar needle was used to evaluate 5 leg muscles and the lumbar paraspinal muscles.

MAIN OUTCOME MEASURES: Presence or absence of radiculopathy using different electrodiagnostic criteria.

RESULTS: When only positive sharp waves or fibrillations were considered, and at least 2 muscles innervated by the same root level and different peripheral nerves were counted as abnormal, 27.1% (13/48) of participants had positive results for radiculopathy. When at least 30% motor unit action potential changes in the limb muscles were also considered, participants with positive results increased to 45.8% (22/48), which was significant when compared with the first criterion (P=.002). When the mini-paraspinal mapping (MiniPM) test as well as at least a 30% motor unit cutoff was used, participants with positive results increased to 50% (24/48), which was significant when compared with the first criterion (P=.001).

CONCLUSIONS: In addition to the presence of positive sharp waves or fibrillations, considering greater than or equal to 30% motor unit action unit potential changes as well as the MiniPM score maintains good specificity and improves the ability of the needle electromyography study to detect lumbar radiculopathy in subjects with radiating low back pain.