Diagnostic accuracy of electrodiagnostic testing in the evaluation of weakness

Electrodiagnostic testing is often used in the evaluation of patients presenting with weakness, but the diagnostic accuracy of the test in this setting is unknown. We prospectively identified 100 patients presenting to our electromyography (EMG) laboratory with the chief complaint of weakness, and compared their referring diagnosis with the electrophysiological diagnosis reached after electrodiagnostic testing. We reviewed each patient's medical record 9 months after EMG to yield a final diagnosis. Electrodiagnostic testing led to a single diagnosis in 79% of the cases; in 31%, this diagnosis was unsuspected by the referring clinician. Adequate follow-up was available for 79% of the patients. The electrodiagnostic testing resulted in a single, correct diagnosis in 73% of the patients and provided more than one possible diagnosis, one of which was correct, in an additional 18%, for an overall diagnostic accuracy of 91% in this group of patients presenting with weakness.