Infectious diseases are the most common type of systemic disease to manifest otologic pathology. 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 otologic disease has often depended on circumstantial evidence, including an associated viral illness, like an upper respiratory infection, or demonstration of seroconversion during the time of hearing loss. In other cases, more direct evidence exists such as with CMV infection, where DNA has been amplified using PCR from perilymph obtained during cochlear implantation in children previously diagnosed with congenital infection (1
Cytomegalovirus (CMV) is a large double-stranded DNA virus belonging to the herpes virus family. Its name derives from the typical appearance of infected tissues, containing massively enlarged cytomegalic inclusion cells. CMV is the most common congenital infection in the world. One percent of babies born in the United States 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 (2
). Of those babies that survive the neonatal period, the majority will have severe neurologic deficits and a severe bilateral SNHL. Possibly more significant, from an epidemiologic point of view, is hearing loss that develops in those children with apparently asymptomatic congenital CMV infection; between 7% and 15% of these infants will go on to develop SNHL. Most cases will be mild, but up to a quarter will be severe (3
). 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.
Varicella-zoster virus (VZV) is a herpes virus that results in varicella or chickenpox with primary infection. Once the 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 Ramsay-Hunt syndrome, or herpes zoster oticus. Involvement of the facial nerve results in the classical presentation of deep otalgia, vesicular eruptions on the external ear and tympanic membrane, and facial palsy. Extension of the inflammatory process to involve the vestibulocochlear nerve may result in SNHL and vertigo.
Most bacterial infections involving the inner ear represent extension of inflammation or infection from the middle ear or CNS. 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, vertigo, and vegetative symptoms.
Similarly, in patients with meningitis, bacteria may invade the labyrinth via the internal auditory canal or the cochlear aqueduct. SNHL is a common complication of meningitis, particularly in children. Up to a third of patients with bacterial meningitis sustain some loss of hearing. The hearing loss is typically bilateral and stable, though it may be unilateral and progressive or fluctuating. Male sex, CT scan evidence of elevated intracranial pressure, nuchal rigidity, low cerebrospinal fluid (CSF) glucose levels, and Streptococcus pneumoniae as the infective agent all are associated with an increased incidence of postmeningitic SNHL.
Syphilis was historically a common cause of otologic dysfunction though this late manifestation of the disease is uncommon today in the developed world. Syphilis is caused by infection with Treponema pallidum
, which may be transmitted transplacentally (congenital syphilis) or through sexual contact (acquired syphilis). Though the incidence of syphilis peaked in the United States in the 1940s and has since declined, there has recently been an increase in the incidence among male homosexuals and patients with HIV (7
). Syphilis is characterized by classic symptomatic stages interspersed with periods lacking significant symptoms. Primary syphilis is typically seen in the acquired form and is characterized by the presence of a chancre (a painless, nonpurulent, and indurated ulcer
in the region of sexual contact), which usually appears 3 weeks after initial infection. Although usually solitary, multiple ulcers may be seen in HIV-infected patients (7
); however, chancres may go unnoticed and may only be seen in a third of cases (9
). Symptoms can last from 3 to 90 days, but often go unnoticed (10
). Secondary syphilis occurs weeks after the chancre has healed and is characterized by a variety of mucosal and cutaneous lesions that appear 2 to 12 weeks after initial infection (it may overlap the primary stage in up to 75% of HIV-infected patients) as well as the presence of constitutional symptoms such as fever and malaise. Asymptomatic meningitis may occur in up to 40% of patients (10
), although associated sudden progressive bilateral hearing loss and vertigo are rare (11
). Other organ systems may be involved, including the liver, kidney, eyes, and joints. The latent phase follows, which is characterized by a lengthy period free of symptoms. Tertiary syphilis, which is similar to late congenital syphilis, manifests years after initial infection. It is characterized by cardiovascular, gummatous, and neurologic involvement. Approximately 15% to 40% of untreated patients will progress to the third stage (7
). Neurosyphilis is composed of meningovascular and parenchymal lesions that can lead to demyelination (tabes dorsalis), motor weakness, and sensory loss.
The diagnosis of syphilis depends on clinical findings, histologic examination of lesions, and serologic testing for syphilis. The Venereal Disease Research Laboratory screening test and rapid plasma reagin are useful screening tests, but lack sufficient sensitivity for both early and late syphilis (10
). Treponemal tests, such as the fluorescent treponemal antibody absorption (FTA-ABS) test or a microhemagglutination test for T. pallidum
, have higher sensitivity and specificity, and are often required for diagnosis. In fact, routine serologic testing for otosyphilis is recommended in all cases of idiopathic progressive SNHL (12
). In addition, the diagnosis of neurosyphilis may require testing of CSF (10
The otologic manifestation of syphilis presents as both hearing and vestibular dysfunction. Sensorineural hearing is very common from both in congenital and the later stages of acquired syphilis. It can be present in up to 40% of patients with congenital syphilis and up to 80% to 90% of patients with neurosyphilis (13
). In addition, many patients present with vestibular dysfunction similar to that seen with Ménière disease (14
). In fact, it has been reported to be present in up to 7% on patients thought to have Ménière disease (11
). Left untreated, however, otogenic syphilis has a more aggressive course than Ménière disease, commonly involving both ears and leading to profound deafness. Physical exam reveals signs consistent with SNHL and peripheral vestibular loss. Hennebert sign (vertigo and nystagmus induced with air pressure to the middle ear) and Tullio phenomenon (vertigo and nystagmus caused by loud noise) may be associated with tertiary syphilis.
The changes in the inner ear resulting from syphilis have been well described. The otic capsule may be involved during the secondary and/or tertiary stages of infection. Involvement manifests as osteitis of the otic capsule bone. Inflammation is mediated by mononuclear cells and results in patchy bone reabsorption; these spaces are subsequently filled with fatty marrow and loose connective tissue (15
). It is accompanied by an obliterative endarteritis typical of syphilitic infection. In severe cases, gumma (lymphocytic infiltrates, vascular occlusion, and central necrosis) may be noted in the otic capsule. In addition, degeneration of the labyrinthine membrane, endolymphatic hydrops, and fibrosis have been described (16
). The peripheral vestibular system may also be involved during the second stage of infection, in which both the VIII cranial nerve and labyrinth are involved in fulminant meningoneurolabyrinthitis.
Penicillin-based antibiotics (or an alternate if allergic) are the treatment of choice, with duration varied by stage of disease. The use of corticosteroids in the treatment of otogenic syphilis is controversial (11
). The prognosis for hearing loss in otogenic syphilis is poor, with hearing improvement seen in less than one-third of treated patients (13
SNHL has also been reported in association with infection by 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 skin, CNS, heart, joints, and the 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 also been reports of sudden SNHL or a Ménière-like syndrome.