Acoustic reflex characteristics in hypo- and hyperthyroid patients.

The various parameters of the stapedial reflex, evoked by acoustic stimuli and recorded using an impedance meter, were evaluated in untreated hyperthyroid and hypothyroid patients and in normal controls. In hyperthyroid patients neither the threshold nor the latency time, the rise time, the recovery time and the maximal amplitude of the reflex were different from normal subjects. On the contrary, hypothyroid patients showed a longer recovery time and a reduced maximal amplitude, suggesting, in the absence of alterations of middle ear structures, a weaker contractile activity of the stapedial muscle.