Idiopathic sudden sensorineural hearing loss in Japan

Figures & data

Table I. Criteria for diagnosis of sudden deafness*.

Main symptoms

Sudden onset

Sensorineural hearing loss, usually severe

Unknown etiology

For reference

Hearing loss (i.e. hearing loss of 30 dB or more over three consecutive frequencies)

Sudden onset of hearing loss, but may progressively deteriorate over 72 h

No history of recurrent episodes

Unilateral hearing loss, but may be bilateral at the onset

May be accompanied by tinnitus

May be accompanied by vertigo, nausea, and/or vomiting, without recurrent episodes

No cranial nerve symptoms other than from cranial nerve VIII

Definite diagnosis: all of the above main symptoms are present

*These criteria were established by the Research Committee of the Ministry of Health, Labour and Welfare in Japan in 2012.

Figure 1. The three prefectures selected for the epidemiological study of sudden sensorineural hearing loss (SSNHL) in Japan.

Table II. Criteria for the grading of hearing loss in idiopathic sudden sensorineural hearing loss (SSNHL)*.

Grade	Criteria
1	PTA <40 dB
2	40 dB ≤PTA <60 dB
3	60 dB ≤PTA <90 dB
4	90 dB ≤PTA

*This grading system was established by the Research Committee of the Ministry of Health and Welfare in Japan in 1988. This grading system is used for evaluation of the initial audiogram recorded for patients within 2 weeks after the onset. ‘a’ is appended for patients with vertigo, and ‘b’ is appended for patients without vertigo (e.g. grade 3a, grade 4b). PTA, arithmetic mean of the five frequencies; the five frequencies are 250, 500, 1000, 2000, and 4000 Hz.

Table III. Hearing improvement as defined by the Ministry of Health and Welfare in Japan*.

Status	Criteria
Complete recovery	All five frequencies of final audiograms are 20 dB or less, or improvement to the same degree of hearing in the unaffected ear
Marked improvement	PTA improvement ≥30 dB
Slight improvement	10 dB ≤PTA improvement <30 dB
No change	PTA improvement <10 dB

PTA, arithmetic mean of the five frequencies; the five frequencies are 250, 500, 1000, 2000, and 4000 Hz.

*These criteria were established in 1988.

Table IV. Results of the epidemiological survey in three prefectures in Japan.

Source		Ehime			Aichi			Iwate
		Response rate	Average number of patients	No. of patients	Response rate	Average number of patients	No. of patients	Response rate	Average number of patients	No. of patients
University hospitals		1 (1)	42.0	42.0	5 (5)	49.6	248.0	1 (1)	75.0	75.0
Other hospitals	400 beds or more	6 (6)	19.0	114.0	28 (31)	33.6*	1041.9	2 (2)	21.5	43.0
	200–399 beds	5 (6)	12.4	74.4	13 (18)	16.2*	292.1	3 (3)	7.0	21.0
	< 200 beds	2 (3)	17.3†	52.0	10 (12)	6.0*	72.0	2 (2)	5.0	10.0
Private clinics		55 (66)	11.2	736.6	214 (307)	9.6*	2931.8	34 (34)	12.7	432.0
Population (thousand)		1415			7427			1303
Incidence/100 000 (95% CI)		72.0 (66.0–78.1)		61.7 (57.3–66.1)			44.6

Response rate: the numbers of hospitals and private clinics that responded are shown, with the numbers approached to participate in this study shown in parentheses. When patients were referred to hospitals from private clinics, they were calculated as being patients of hospitals. The number of patients from private clinics indicates that they visited only private clinics. The estimated number of patients was obtained by assuming that the number of patients was the same between hospitals that did and did not respond, taking into account the size of the hospital. The number of ENT outpatients was not significantly different between hospitals that did and did not respond in each size of hospital.

*In Aichi, 9 hospitals and 67 private clinics only reported the number of patients who visited from April through October. The average number of patients was estimated by assuming no seasonal difference in these hospitals and clinics.

^†Of 3 hospitals with less than 200 beds in Ehime, 1 specialist hospital, providing mainly ENT services, reported 42 patients. It was assumed that the number of patients in the ordinary hospital that did not respond was five, as for another ordinary hospital.

Figure 2. Distribution of annual incidence of sudden sensorineural hearing loss (SSNHL) for men and women, in each age group.

Table V. Final hearing outcome in each grade of sudden sensorineural hearing loss (SSNHL).

Grade	Complete recovery	Marked improvement	Slight improvement	No change	Total
1	85	0	5	36	126
2	30	5	24	22	81
3	25	23	11	20	79
4	1	9	7	7	24
Total	141	37	47	85	310