Abnormal decay that recovers after rest

History

A 41-year-old reports drooping eyelids that worsen through the day and occasional double vision. Pure-tone hearing is normal bilaterally and tympanometry is type A. Acoustic reflexes are present at normal thresholds. On reflex decay testing at 1000 Hz the amplitude falls below 50% within the 10-second hold; after a few minutes of rest, the test is repeated and the decay is markedly less pronounced.