Viruses

The most common cause of childhood sensorineural hearing loss (SNHL) is congenital cytomegalovirus (CMV) infection (Chapter 247). The strongest predictor of delayed hearing loss appears to be the presence of symptoms at birth; prolonged viral shedding may also be a risk factor. In one large study, children who passed initial audiologic examinations but who had CMV-related symptoms at birth were ~6 times more likely to develop hearing loss than those who were asymptomatic. Stabilization or perhaps reversal of the hearing loss may be possible by using ganciclovir in very young infants with congenital CMV infection.

Other viral causes of SNHL include congenital rubella as well as acquired mumps, rubella, rubeola (measles), and fifth disease, caused by parvovirus B19. Many other viruses also occasionally are associated with SNHL. In as many as 50% of cases, hearing loss, which usually is bilateral and often is asymmetric, progresses and worsens over weeks to years.

Before an effective vaccine was introduced, rubella was responsible for as many as 60% of cases of childhood SNHL. Vaccination in developed countries has reduced the rate of rubella by >97%. Similarly, measles and mumps are now uncommon causes of SNHL in the USA because of successful vaccination programs.

Herpes simplex encephalitis can also be associated with SNHL, which is more common in children with congenital herpesvirus infection. Acyclovir and other antiviral agents can help the hearing loss and other central nervous system manifestations (Chapter 237).

Toxoplasmosis

Toxoplasma gondii is a protozoan that can cause congenital SNHL. In the USA, about 3,000 children are born each yr with congenital toxoplasmosis, and approximately 25% of untreated patients have SNHL. If maternal infection is documented during the fetal period, medical therapy may be able to prevent some of the clinical manifestations, including SNHL of the offspring (Chapter 282).

Bacterial Meningitis

Since the Haemophilus influenzae type b vaccine was introduced, Streptococcus pneumoniae (Chapter 175) and Neisseria meningitides (Chapter 184) have become the leading causes of bacterial meningitis in children in the USA. Hearing loss occurs more commonly with S. pneumoniae, with an estimated incidence of 15-20%. Approximately 60% of the associated hearing loss is bilateral, although it often is asymmetric. If hearing loss is present at the time of presentation with meningitis, and especially if it is severe to profound, the likelihood of significant improvement is low. However, if the hearing loss develops after admission for treatment and is not severe, stabilization or improvement is possible. Late progression of SNHL also has been noted in some children years after meningitis. In the USA and many other developed countries, bacterial meningitis is one of the major causes of profound deafness leading to cochlear implantation in children. The introduction of pneumococcal conjugate vaccine is expected to lead to a reduction in SNHL due to pneumococcal meningitis, although pneumococcal strains not sensitive to the vaccine appear to be associated with rates of deafness equivalent to those that are sensitive.

Studies have shown favorable trends in the course and outcome after administration of dexamethasone for hearing loss and other neurologic deficits associated with bacterial meningitis (Chapter 595.1), although its effectiveness, especially for S. pneumoniae and N. meningitidis meningitis, generally has not reached statistical significance because of the small number of cases in the trials. Dexamethasone has been shown to reduce severe hearing loss associated with H. influenzae type b meningitis regardless of the timing of administration of dexamethasone (before or with antibiotics vs. later) or of the antibiotic used. For pneumococcal meningitis, dexamethasone might confer benefit only when given early and only for protection against severe hearing loss.

Syphilis

Congenital syphilis, caused by Treponema pallidum, causes SNHL in 3-38% of affected children (Chapter 210). The exact incidence is difficult to ascertain, because the hearing loss might not develop until adolescence or even adulthood. When the condition is identified, treatment with antibiotics and corticosteroids can improve the hearing loss.

Other Diseases of the Inner Ear

Labyrinthitis may be a complication of direct spread of infection from acute or chronic otitis media (OM) or mastoiditis and also can complicate bacterial meningitis as a result of organisms entering the labyrinth through the internal auditory meatus, endolymphatic duct, perilymphatic duct, vascular channels, or hematogenous spread. Clinical manifestations of labyrinthitis can include vertigo, dysequilibrium, deep-seated ear pain, nausea, vomiting, nystagmus, and SNHL. Acute suppurative labyrinthitis, characterized by abrupt, severe onset of these symptoms, requires intensive antimicrobial therapy. If it is secondary to OM, otologic surgery may be required to remove underlying cholesteatoma or drain the middle ear and mastoid, in addition to antibiotics. Acute serous labyrinthitis, with milder symptoms of vertigo and hearing loss, can develop secondary to middle-ear infection as well. It usually responds well to antibiotics and corticosteroids, with improvement in both vertigo and hearing. Chronic labyrinthitis, most commonly associated with cholesteatoma, manifests with SNHL and vestibular dysfunction that develops over time; surgery is required to remove the cholesteatoma. Chronic labyrinthitis also occurs uncommonly secondary to long-standing OM, with the slow development of SNHL, usually starting in the higher frequencies, and possibly with vestibular dysfunction. Additionally, and more commonly, children with chronic middle-ear fluid often are unsteady or off balance, a situation that improves immediately when the fluid resolves.

Otosclerosis, an autosomal dominant disease that affects only the temporal bones, causes abnormal bone growth that can result in fixation of the stapes in the oval window, leading to progressive hearing loss. In one series in North America, otosclerosis was found in 0.6% of temporal bones of children < 5 yr and 4% of those ages 5-18 yr. The hearing loss is usually conductive at first, but SNHL can develop. White girls and women are affected most commonly, with onset of otosclerosis in teenagers or young adults, often associated with pregnancy. Corrective surgery to replace the stapes with a mobile prosthesis often is successful.

Osteogenesis imperfecta (OI) is a systemic disease that can involve both the middle and inner ears (Chapter 692). Hearing loss occurs in about 20% of young children and as many as 90% of adults with this disease. The hearing loss most commonly is conductive because of abnormalities of the ossicles, but SNHL can occur if other areas of the otic capsule become affected. If the hearing loss is severe enough, a hearing aid may be a preferable alternative to surgical correction of the fixed stapes, because stapedectomy in children with OI can be technically very difficult, and the disease and the hearing loss may be progressive.

Osteopetrosis, a very uncommon skeletal dysplasia, can involve the temporal bone, including the middle ear and ossicles, resulting in a moderate to severe, usually conductive hearing loss. Recurrent facial nerve paralysis also can occur as a result of excess bone deposition; with each recurrence, less facial function might return (Chapter 690).