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Hearing loss is an uncommon presenting symptom of a systemic infectious disease but may develop during the course of several viral and bacterial infections. Pathogens may infect the inner ear and auditory pathways in utero, resulting in congenital syndromes that often include deafness, or infection may be acquired after birth. As the fluids of the inner ear are not easily accessible for sampling, the implication of viral pathogens as the causes of sensorineural hearing loss has often depended on circumstantial evidence, including an associated viral illness—for example, an upper respiratory infection—or demonstration of seroconversion during the time of hearing loss.

Cytomegalovirus. Cytomegalovirus (CMV) is a large, double-stranded DNA virus belonging to the herpesvirus family. Its name is derived from the typical appearance of infected tissues, containing massively enlarged cytomegalic inclusion cells. CMV is the most common congenital infection in the world. Of babies born in the United States, 1% are infected; the likely route of infection is transplacental. Of these babies, 10% will exhibit symptomatic infection or cytomegalic inclusion disease, almost exclusively when primary maternal infection occurs during pregnancy. Of those babies that survive the neonatal period, the majority will have severe neurologic deficits and severe bilateral sensorineural hearing loss. Possibly more significant, from an epidemiologic point of view, is hearing loss that develops in those children with apparently asymptomatic congenital CMV infection (9).

Between 6% and 23% of these infants will go on to develop sensorineural hearing loss. Most cases will be mild, but up to one-quarter will be severe. Hearing loss may be unilateral or bilateral and may develop months or years after birth and be missed on routine audiometric screening. It is thought that asymptomatic CMV infection causes 20% to 30% of congenital hearing loss. In the healthy adult, CMV infection is usually asymptomatic or may cause a mononucleosis-like syndrome. In human immunodeficiency virus (HIV)-infected or transplant patients, severe multisystemic disease may ensue, but hearing loss is not common.

Rubella. Rubella is a member of the Togaviridae family. The significance of this virus is that primary maternal infection during the first trimester of pregnancy may result in the congenital rubella syndrome. Sensorineural hearing loss is the most common manifestation, seen in up to 60% of affected infants. Hearing loss may be bilateral or unilateral, may manifest as late as the second year of life, and may be the only sign of infection (10). Other features are ocular malformations including cataracts and retinopathy, cardiac malformations, and CNS disease. Postnatal infection produces German measles, a mild viral illness.

Varicella-Zoster Virus. Varicella-zoster virus (VZV) is also a herpes virus. Primary VZV infection results in varicella, or chickenpox. Once primary infection is cleared, VZV remains dormant in the dorsal root ganglia. Reactivation of the virus, often during periods of suppressed cellular immunity, results in shingles, or a dermatomal vesicular eruption. Reactivation of VZV in the geniculate ganglion results in a painful vesicular eruption in the external ear, known as herpes zoster oticus. When facial paralysis accompanies these other symptoms, the disorder is known as Ramsay Hunt syndrome. Extension of the inflammatory process to involve the vestibulocochlear nerve may result in sensorineural hearing loss and vertigo.

Mumps and Measles Viruses. Mumps and measles viruses are members of the paramyxoviridae family; infection is rare in the developed world since vaccination began, although it is common worldwide. Mumps infection commonly presents with unilateral or bilateral parotitis and orchitis in males. Sensorineural hearing loss is uncommon, affecting less than 0.05% of patients, and tends to be unilateral. Similarly, hearing loss is uncommon in measles infection, seen in approximately 0.1% of patients (10). The classic presentation of measles involves cough, coryza, conjunctivitis, white oral mucosal lesions known as Koplik spots, and a maculopapular rash.

Human Immunodeficiency Virus. HIV infection is associated with a significant incidence of sensorineural hearing loss, although this relationship is not fully understood. The etiology is likely variable and includes a high incidence of middle-ear disease, opportunistic infections and malignancies of the CNS, viral labyrinthitis and neuritis, meningitis, and ototoxicity from medications used to treat HIV infection and its complications (11). HIV is discussed in detail in Chapter 16.

Meningitis. Most bacterial infections involving the inner ear represent extension of inflammation or infection from the CNS, or, less commonly, the middle ear. Meningitis may result in bacterial invasion of the labyrinth via the internal auditory canal or the cochlear aqueduct. Sensorineural hearing loss is a common complication of meningitis, particularly in children. Up to one-third of patients with bacterial meningitis sustain some loss of hearing (12). The hearing loss is typically bilateral and stable, though it may be unilateral and progressive or fluctuating. Male sex, computed tomography (CT) scan evidence of elevated intracranial pressure, nuchal rigidity, low cerebrospinal fluid (CSF) glucose levels, and Streptococcus pneumoniae as the infective agent are all associated with an increased incidence of postmeningitic sensorineural hearing loss (13).

Otitis Media. Acute otitis media can produce a sterile serous labyrinthitis secondary to the passage of bacterial toxins and inflammatory mediators into the inner ear fluids, likely through the round window or a dehiscent lateral semicircular canal in patients with chronic middle-ear disease and cholesteatoma. This typically causes a mild high-frequency hearing loss. Entrance of bacteria into the inner ear will lead to a suppurative labyrinthitis, which is heralded by severe hearing loss and vertigo (14).

Syphilis. Syphilis may cause sensorineural hearing loss in its congenital or acquired form. The disease is caused by a spirochete, Treponema pallidum. Infection may be sexually transmitted or may be acquired in utero. Congenital infection usually spreads through the placenta, although it may be acquired during delivery, and most commonly occurs with maternal primary or secondary infection during pregnancy. There is a high incidence of stillbirth in fetuses infected with syphilis; of those that are born alive, one of two syndromes may result. Early congenital syphilis refers to manifestations within the first two years of life and is usually fatal. It occurs as a result of active systemic infection. Symptoms of early congenital syphilis include skeletal malformations, organomegaly, rash, CNS disease, and syphilitic rhinitis (snuffles) productive of purulent secretions rich in spirochetes. Late congenital syphilis presents after the age of two and results from residual scarring and inflammation from earlier infection; it may present with hearing loss in childhood but also as late as the third or fourth decade of life (15). The hearing loss can present suddenly and may be associated with vestibular symptoms (16). Hutchinson's triad of late congenital syphilis includes Hutchinson's teeth (notched central incisors), interstitial keratitis of the eye, and sensorineural hearing loss.

Acquired syphilis is sexually transmitted in almost all cases. The course and pathogenesis of the disease is elaborate. The spirochete penetrates intact mucous membranes and spreads systemically long before the primary lesion appears. The primary lesion is the chancre, a painless ulcerative lesion at the site of inoculation associated with regional lymphadenopathy; it heals in four to six weeks. Secondary syphilis represents disseminated infection and appears 6 to 12 weeks after the primary lesion. Constitutional symptoms, a maculopapular rash involving the palms and soles, condyloma lata, and mucous patches are the most common manifestations. With resolution of untreated secondary disease, a period of latency begins. The late or tertiary manifestations of syphilis appear years after the primary infection, although they probably represent the end-stage of a pathologic process that began with inoculation. The major categories of tertiary syphilis include neurosyphilis, cardiovascular syphilis that may result in aortic aneurysms, and gummas, which are benign granulomatous lesions that may occur anywhere in the body (17).

Hearing loss can be associated with early or late acquired syphilis. Sensorineural hearing loss arising during the secondary stage of syphilis is thought to result from a basilar meningitis affecting the cochlear nerve. This appears as a sudden, rapidly deteriorating, bilateral hearing loss. Luetic labyrinthitis may develop as part of late acquired syphilis and presents in a variable manner with asymmetric involvement being common. Vestibular symptoms may be more prominent than hearing loss. Gummas may form along the brainstem, the eighth nerve, and the temporal bone and vestibule and result in sensorineural hearing loss (16). Syphilis is discussed in greater detail in Chapter 15.

Lyme Disease. Sensorineural hearing loss has also been reported in association with infection with another spirochete, Borrelia burgdorferi, the causative organism of Lyme disease. The organism is introduced into the skin by the bite of an infected tick of the genus Ixodes. The spirochete has particular tropism to the skin, CNS, heart, joints, and eyes. It is not fully clear which features are a result of disseminated infection and which result from the systemic inflammatory response. In the head and neck, Lyme disease is most commonly associated with facial paresis, particularly in children. There have been reports of sudden sensorineural hearing loss or a Meniere's-like syndrome in Europe (Selmanzi Z), although there has yet to be an association between Lyme disease and inner-ear pathology in North America (18,19).

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