[Changes in hearing features according to days from onset of sudden deafness].

We analyzed 746 patients with idiopathic sudden hearing loss who visited our clinic within 16 days after the onset. Patients were divided into 10 groups according to the number of days between the initial visit and the onset. Initial hearing levels, audiometric types and hearing recoveries were investigated in these groups to estimate the natural history of sudden deafness. The results were as follows: 1) There were no significant differences among the 10 groups regarding the averaged five-frequency hearing levels of initial audiograms. 2) Regarding the audiometric types of the initial audiograms, flat and upward slope types were frequently seen in the groups who visited us within 6 days. In contrast, the population of down slope types gradually increased in the groups presenting after 7 days. In the ultimate audiograms, flat and down slope types were frequently seen in all groups. 3) There were significant differences among the 10 groups regarding the averaged five-frequency improvement (one-way analysis of variance, p < 0.01). After 9 days, hearing recovery became less likely.