The stapedius reflex in the diagnosis of myasthenia gravis

The contralateral stapedius reflex, elicited by a clearly-defined auditory stimulus, was studied in 3 patients with myasthenia gravis. The reflex was assessed by recording the change which occurred in the acoustic impedance of the middle ear. In all patients a decay (decrement) of the reflex was found, interpreted as a sign of increased fatiguability at the neuromuscular junction of the stapedius muscle. The reflex recovered rapidly after the intravenous injection of a cholinesterase inhibitor (Tensilone̊g;). It is concluded that the stapedius reflex test can be of value in the diagnosis of myasthenia gravis, since it can be well-standardized, involves a muscle innervated by the facial nerve and is not disturbing to the patient, whose active cooperation is not necessary.