Stapedius reflex decay test in diagnosis of myasthenia gravis (MG).

Stapedius reflex decay test (SRDT) was attempted in 30 patients with suspected myasthenia gravis (MG). In 43% of the sample measurement of the decay was not possible because of an audiologic abnormality, reflex threshold too high for safe testing or absence of the reflex with no obvious cause. A control group of 24 normal subjects showed a large variance and thus only a decay, after 5 minutes of stimulation, greater than 50% of the original value was considered abnormal. Out of 17 patients in whom SR decay was successfully measured, 7 (41%) had an abnormal value. Sensitivity of the test was found at 80%, specificity at 75%, when the clinical diagnosis of MG, upheld in follow-up, was taken as a criterion. The percentage of concordant abnormal findings was 50% for repetitive electrical stimulation of a peripheral nerve, 60% for positive effect of anticholinesterase drugs, 100% for presence of ACh receptor antibodies.