idiopathic sudden deafness : risk factors from a case-control study using pooled controls mieko...

Idiopathic Sudden Deafness: risk factors

from a case-control study using pooled controls

Mieko Nakamura, MD PhDNobuo Aoki, MD PhDDepartment of Hygiene

Hamamatsu University School of MedicineJAPAN

Learning objectives

To learn

• Definition of idiopathic sudden deafness

• Analyses using a database of pooled controls

• Qualitative assessment on diet

0

50

100

150

200

1971-1973

1987 1993

/million/year

Frequencies of sudden deafness in Japan

– an increasing trend

Proposed etiological mechanisms

• Vascular impairment

• Viral infection

• Others

Blood supply in Cochlea

Subclavian artery Vertebral artery ⇒ ⇒Basilar artery Anterior inferior cerebellar ⇒artery

⇒ Common cochlear artery

⇒ Common modiolar vein

⇒ arterioles and venules intricate capillary beds

Cochlea

A schematic drawing of inner ear

High tone frequencyhearing (20,000Hz)

Low tone frequencyhearing (20Hz)

Scala vestibuliScala tympani

Vestibular apparatus

Helicotrema

Aim of a case-control study

To know

• Associations of traditional cardiovascular risk factors

• Similarities and differences of the associations among types of hearing loss

Cases

• October 1996 - August 1998

• Patients diagnosed with idiopathic sudden deafness according to criteria established by Japan’s Sudden Deafness Research Committee

• Having an audiogram within 14 days of onset

Definition of idiopathic sudden deafness

• Sensorineural hearing loss of sudden onset

• No involvement of cranial nerves other than the eighth nerve

• No known etiology

Patterns of hearing loss definition

• High-frequency hearing loss

• Low-frequency hearing loss

• Flat-type hearing loss

• Profound hearing loss

• Other

Patterns of hearing loss (mean-SD)

250Hz 500Hz 1kHz 2kHz 4kHz 8kHz120

dB 0

250Hz 500Hz 1kHz 2kHz 4kHz 8kHz

250Hz 500Hz 1kHz 2kHz 4kHz 8kHz250Hz 500Hz 1kHz 2kHz 4kHz 8kHz 250Hz 500Hz 1kHz 2kHz 4kHz 8kHz

High-frequency (n=20) Low-frequency (n=31)

Flat-type (n=54) Profound (n=20) Other (n=39)

Low High

Controls

• Selected from a database of pooled controls

• The information in the database was obtained between 1987 and 1994

• Matched to cases on age (in five-year bands), gender, and residential district

Questionnaire

• Identical for cases and controls

• Food intake frequencies, tobacco, alcohol, sleeping hours, etc

Statistical methods

• m : n matching

• Odds ratios and 95% confidence intervals were estimated using conditional logistic regression for group matching, where the matching variables were age, gender, and residential district

Qualitative assessment on diet

• Frequencies of intake about 31 foods and 4 drinks were obtained

• New indexes (“Western” food intake and “Japanese” food intake) were created based on principal component factor analysis performed for these data

Factor analysis

0.5

Second factor

"Japanese" foods

"Western" foods

1

2

3

45

67

8

31

19

11

910

34

27

15 12 3017

22 1623

24 25

1426

33

28

21

13 29

32

18

20

35

Firstfactor0.50

Line of Equality

“Western” food intake

• Calculated by summing the frequencies of intake for each of the foods in the “Western” food group

• On the basis of these scores: frequent intake (highest quartile) moderate intake (middle two quartiles)

infrequent intake (lowest quartile)

“Japanese” food intake

• Calculated by summing the frequencies of intake for each of the foods in the “Japanese” food group

• On the basis of the scores: frequent intake (highest quartile) moderate intake (middle two quartiles)

infrequent intake (lowest quartile)

Odds ratios of sudden deafness for “Western” food intake

0.0

1.0

2.0

3.0

4.0

Infrequent Moderate Frequent

All types High-frequency Low -frequencyFlat-type Profound Other

Odds ratios of sudden deafness for “Japanese” food intake

0.0

1.0

2.0

3.0

4.0

Infrequent Moderate Frequent

All types High-frequency Low -frequencyFlat-type Profound Other

Odds ratios of sudden deafness for alcohol intake

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 >0 and <2 >=2 units/ day

All types High-frequency Low -frequencyFlat-type Profound Other

Odds ratios of sudden deafness for cigarette smoking

0.0

1.0

2.0

3.0

4.0

0 >0 and <20 >=20 / day

All types High-frequency Low -frequencyFlat-type Profound Other

Odds ratios of sudden deafness for sleep duration

0.0

1.0

2.0

3.0

4.0

<7 >=7 and <8 >=8 hours

All types High-frequency Low -frequencyFlat-type Profound Other

Lifestyle factors and idiopathic sudden deafness

A hypothesisModerate alcohol intake coagulation ↓ fibrinolysis →

Western diet (rich in saturated fatty acids) coagulation ↑ serum cholesterol ↑

Smoking microcirculatory/haemo- static abnormalities vasospasm

Heavy alcohol intake fibrinolysis ↓ vasospasm

Vascular impairment in cochlea ?

Westernization of food intake in Japan

050

100150200250300350400(g

/ capita/ day)

rice meatsWorld War II

Summary

Increased risks with

• high intake of "Western" diet

• high intake of alcohol

• low intake of traditional “Japanese” diet

Similar associations of diet among types of hearing loss