Clinical Reasoning: A Woman With Subacute Progression of Distal Upper Extremity Weakness.

A 65-year-old woman presented with 3 months of progressive hand weakness, initially with distal-predominant symptoms. EMG was notable for diminished amplitudes in bilateral radial nerves without evidence of conduction block and with normal sensory nerve action potentials. Anti-acetylcholine receptor and antistriated muscle antibodies were positive, but subsequent EMG did not reveal abnormalities on repetitive nerve stimulation. Muscle biopsy was performed, revealing extensive inflammatory infiltrates with significant associated fibrosis. This case discusses the approach to localization within the motor pathway and the use of serologic studies, imaging, and electrodiagnostic testing to supplement history and examination.