Causes of Hearing Loss — Congenital CMV, Genes, Mumps, Drugs, Noise and Ageing

1. How it appears in the exam

2. Causes by type of hearing loss

The causes covered in this article line up as in Figure 1.
Some hearing loss is mixed, with features of both, and some has no clear cause.

3. Hearing loss present at birth

Babies with hearing loss in both ears are born at a rate of 1 to 2 per 1,000 births, which makes it one of the more common congenital conditions.

Genetic hearing lossSensorineural

About 60% of congenital hearing loss is genetic. More than 120 genes have been identified, and the most common is GJB2; GJB2 variants are found in about 20% of congenital hearing loss. Since fiscal 2012, genetic testing for congenital hearing loss has been covered by Japan’s public health insurance.

Hearing loss that comes with other symptoms is called syndromic hearing loss. The three names that come up most often are below.

Congenital cytomegalovirus (CMV) infectionSensorineural

If a mother catches cytomegalovirus during pregnancy and it passes to the baby, the child may be born with hearing loss, microcephaly or other conditions. In Japan an infected baby is born in about 1 in 300 births, and about 30% of them are at risk of hearing impairment or other effects.

Diagnosis uses urine taken within 3 weeks of birth. Since January 2018, the urine test for newborns within 3 weeks of birth suspected of congenital CMV has been covered by public insurance. Babies who are referred in newborn hearing screening are advised to have the CMV test within this window (Figure 2 of the hearing-tests article). In March 2023, valganciclovir (brand name Valixa) was approved in Japan to treat symptomatic congenital CMV infection.

Congenital rubella syndromeSensorineural

If a woman without enough immunity to rubella is infected up to about week 20 of pregnancy, the child may be born with congenital heart disease, hearing loss, cataracts and other conditions. This is congenital rubella syndrome (CRS).

Malformations of the sound pathConductive

When the sound path is abnormal — a closed ear canal (atresia), a severely narrowed canal, or a break in the chain of ossicles — the result is conductive hearing loss.

4. Hearing loss acquired after birth

Otitis media and otosclerosisConductive

Otitis media with effusion, a perforated eardrum from chronic otitis media, otosclerosis and the like are conductive losses caused by problems in the outer or middle ear. Surgery can sometimes improve them. Impacted earwax can also make hearing worse. The test that finds otitis media with effusion is tympanometry (see the hearing-tests article).

Mumps deafnessSensorineural

Hearing loss is one of the complications of mumps. In a nationwide survey by the Oto-Rhino-Laryngological Society of Japan, at least 348 people developed mumps deafness over the two years 2015–2016. At their first visit, 317 had loss in one ear and 15 in both, and 274 (about 80%) were left with severe or worse hearing loss.

Among causes acquired after birth, mumps is the leading cause of single-sided deafness. In Japan the mumps vaccine is voluntary, not part of the routine immunisation schedule.

Drug-induced hearing loss (“streptomycin deafness”)Sensorineural

Hearing loss caused by aminoglycoside antibiotics such as streptomycin has long been called sutomai nanchō, “streptomycin deafness.” According to the Ministry of Health, Labour and Welfare’s manual on hearing loss as a serious adverse drug reaction, the damage is to the hair cells of the organ of Corti in the inner ear, the outer hair cells in particular, producing sensorineural loss. At first only the high pitches, 4000–8000 Hz, are often affected.

People with mitochondrial gene variants such as m.1555A>G are highly sensitive to these drugs and can lose hearing even at small doses. The same manual lists, as a question to ask, whether there are people with hearing loss on the mother’s side of the family. Platinum anticancer drugs and loop diuretics are also listed in the manual as drugs that can cause hearing loss.

Sudden hearing lossSensorineural

Hearing in one ear (very rarely both) suddenly gets worse one day. Problems with blood flow or a viral infection are suspected, but the cause is still not known. To recover hearing, starting treatment early is considered important.

Noise-induced hearing lossSensorineural

Listening to loud sound over a long period damages the hair cells of the inner ear. Hearing starts to drop at fairly high pitches around 4000 Hz; hearing once lost is hard to recover, and there is no drug treatment yet. For workplace noise, the Ministry of Health, Labour and Welfare revised its guidelines for preventing noise-induced hearing loss on 20 April 2023.

Age-related hearing lossSensorineural

This is hearing that declines with age; the exam also uses the older name rōjinsei nanchō (presbycusis). It generally starts at high pitches, and in older people it usually affects both ears. It affects not only how loud sounds seem but also the ability to tell words apart (speech discrimination).

5. Points to check before the exam

Closing

WHO says that almost 60% of hearing loss in children can be prevented through measures such as immunisation. Some causes can be prevented once they are known, like rubella and mumps vaccination or noise control at work.

To get a sense of what reduced hearing sounds like, try these tools on the site (in Japanese).

This is one way of organising the topic. Medical explanations can differ in their numbers and wording depending on the source and the year. If you learned it differently in your course, or think something here is wrong, please let me know through the contact form.