The diagnosis of myasthenia gravis can be confirmed most reliably using:

D. Single-fiber EMG.

DISCUSSION: Although findings from a careful history and physical examination are suggestive of the diagnosis of myasthenia gravis, specific diagnostic testing is required to confirm the diagnosis. Elevated anti–acetylcholine receptor antibodies are present in 85% to 90% of patients with generalized myasthenia but are often negative in patients with early or ocular myasthenia gravis. The Tensilon test is also positive in approximately 90% of patients with generalized myasthenia gravis, but both false-negative and false-positive results occur, especially in patients with mild or early disease. Standard EMG studies are helpful if positive, but their overall sensitivity may be as low as 35%. The specialized technique of singlefiber EMG is the most reliable diagnostic test, being abnormal in 90% of patients with mild disease and in virtually 100% in patients with severe generalized myasthenia gravis.