A grading system for sudden deafness has been established by the Research Group on Sudden Deafness of the Japanese Ministry of Health and Welfare. According to this grading system, sudden deafness cases are classified according to the initial hearing level and the vestibular symptoms. Few clinical analyses of sudden deafness cases have been made using this grading system. In this study, 263 sudden deafness cases were classified into 6 groups based on the grading system. All of the cases presented with an initial hearing level of more than 40 dB and underwent treatment within 1 week of the onset of symptoms. The relationship between the grading system and hearing recovery is discussed. Fixed hearing levels with a good prognosis were grades 2b, 2a, 3b, 3a, 4b and 4a. To quantitatively evaluate hearing recovery, the average hearing recovery rate and the percentage of the complete recovery cases were analyzed for each group. Average hearing recovery was ranked into five levels, regardless of the evaluation method. Grades 2b and 3b were the best, and grade 4a was the worst. After grades 2b and 3b, grade 2a was the second best, grade 3a was the third, and grade 4b was the fourth. The cases included in grades 2 and 3 were more strongly effected by whether the cases had vestibular symptoms or not than by their initial hearing levels. When grade 4 cases were classified by their initial hearing level, a large difference existed among grade 4a cases with regard to whether they presented with an initial hearing level of under or more than 100 dB. The hearing recovery of grade 4a cases with an initial hearing level of less than 100 dB was almost the same as that of grade 3a. However, the hearing recovery of grade 4b cases varied only slightly. Consequently, some ranges of initial hearing level exhibited similar degrees of hearing recovery. In cases without vestibular symptoms, the range of initial hearing levels was 40-89 dB. These cases had a 60% chance of complete recovery, and the hearing recovery rate was 80% on average. In cases with vestibular symptoms, the range of initial hearing levels was 60-99 dB. These cases had a 40% possibility of complete recovery, with an average hearing recovery rate of 60%. After comparing the initial grades and the final grades using the same grading system, the majority of grade 2 and 3 cases attained a grade 1 fixed hearing level. However, most grade 4 cases had a grade 3 fixed hearing level.
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