Hearing loss in IMIED may take two forms. First, patients may complain primarily of diminished hearing acuity (the ability to perceive sound). Crude assessments of hearing sensitivity using the mechanical sounds of a watch, the dial-tone of a telephone, or the rubbing of fingers, are inadequate to detect subtle but clinically significant deficits in hearing acuity. Second, patients may also note decreased discrimination (the ability to distinguish individual words). Communication problems arising from poor word discrimination often constitute the chief complaint. Patients with significant deficits in word discrimination are able to hear the sound of a voice on the telephone, but fail to understand what is being said. They also have difficulty participating in conversations conducted amid background noise. Understanding conversations in crowded rooms or restaurants is particularly problematic.
Otoscopy is usually normal in IMIED, even among patients with profound SNHL. In patients with SNHL secondary to granulomatosis with polyangiitis, otoscopy may reveal findings consistent with otitis media caused by granulomatous inflammation within the middle ear cavity, tympanic membrane clouding, or even rupture.
In granulomatosis with polyangiitis, conductive hearing loss caused by middle ear disease is more common than SNHL, but SNHL occurs with a frequency that is probably underrecognized because of failure to obtain audiologic testing in all patients. Conductive hearing loss in granulomatosis with polyangiitis results from a variety of mechanisms, including opacification of the middle ear cleft with fluid or discontinuity of the ossicular ear chain. In contrast, the ischemic sequelae of vasculitis are believed responsible for SNHL. Both vasculitis of the vasa nervorum and compression of the VIIth cranial nerve by granulomatous inflammation as it courses through the middle ear can cause peripheral facial nerve paralysis.
Two simple physical examination tests are useful in distinguishing SNHL from conductive hearing loss: the Weber test and the Rinne test. In the Weber test, a vibrating 512 Hz tuning fork is placed on an upper incisor tooth or mid-forehead. The tone will sound louder in the ipsilateral ear if conductive hearing loss is present, and in the contralateral ear if SNHL is present. The test can be repeated for higher frequencies. In the Rinne test, a vibrating 512 Hz tuning fork is first placed 3 cm from the opening of the ear and then in contact with the mastoid bone. A comparison is made between the loudness of the tone generated in air and that on the bone. A conductive hearing loss of at least 30 dB is suggested when bone conduction exceeds air conduction in loudness. A normal Rinne test (air conduction >bone conduction) in an ear to which the Weber has lateralized, suggests SNHL in that ear.
Otolaryngologists and neurologists, who should become involved in patients’ care if SNHL is suspected, should be expert at evaluating patients’ vestibulo-ocular reflexes (VORs). Other tests, including audiometric testing and electronystagmography, are also essential components of the work-up.
Evaluations of the VORs consist of assessments for nystagmus in response to repetitive head shaking, and for gaze stability during rapid lateral rotation of the head. By detecting head movement, the inner ear provides afferent input to the VOR upon which the central nervous system depends for accuracy in the compensatory saccadic movements of the eyes. Disturbance of the inner ear’s role in maintaining a stable image on the retina leads to a perception of dizziness, which is worsened by head movement and relieved at rest. The rapid changes in afferent input to the central nervous system associated with IMIED lead to VOR decompensation, an inability to maintain a stable retinal image, and a persistent illusion of movement known as vertigo.
The acute phase of vertigo resolves to motion-induced dizziness through central compensation after days to weeks. In the acute phase of vestibular decompensation, spontaneous nystagmus may be seen when visual fixation is suppressed (eg, in the dark or behind Frensel lenses). The VOR can be assessed for each ear separately at the bedside by asking the patient to fix her eyes on the examiner’s nose while the examiner quickly turns the patient’s head 30 degrees toward the ear in question. Normal VORs generate smooth, accurate compensatory ocular saccades. In contrast, abnormal VORs are associated with under- or overshooting of the eye movements, followed by a corrective saccade.
A feeling of perpetual motion known as oscillopsia is a disabling consequence of bilateral VOR loss. The presence of oscillopsia and bilateral vestibular hypofunction can be detected by comparing visual acuity with the Snellen chart while the head is at rest versus during head shaking. A difference in visual acuity of 3 or more lines is an indication of peripheral vestibular dysfunction. Larger decrements are expected in bilateral disease.
Electronystagmography provides objective measure and comparison between ears of peripheral vestibular function, more specifically the lateral semicircular canal. The vestibular electromyographic potential measured in the sternocleidomastoid muscle in response to stimulation of the saccule by low frequency sound assesses another component of peripheral vestibular function.
Cogan syndrome, described in detail in Chapter 42, can be associated with virtually any form of ocular inflammation, including orbital pseudotumor, scleritis, and uveitis. The most characteristic ocular manifestation of Cogan syndrome, however, is interstitial keratitis. Granulomatosis with polyangiitis (see Chapter 32) also has a host of potential ocular complications. Diplopia, amaurosis fugax, and anterior ischemic optic neuropathy are common manifestations of giant cell arteritis. Aside from secondary sicca symptoms, the most common eye problem in SLE (see Chapters 21 and 22) is retinopathy, which may be associated with either retinal vasculitis or a clotting diathesis, such as that associated with antiphospholipid antibodies. Keratoconjunctivitis sicca is a hallmark of Sjögren syndrome (see Chapter 26).
The results of routine laboratory test in IMIED are usually unremarkable. There is typically no indication, for example, of a systemic inflammatory response; acute phase reactants are usually normal. The measurement of several types of autoantibodies is highly appropriate, however, in the search for an underlying cause of SNHL that might have alternative treatment indications. Autoantibodies relevant to the assessment of a patient with SNHL are shown in Table 68–1.
Table 68–1. Autoantibodies and Other Assays Appropriate to the Evaluation of Sensorineural Hearing Loss. ||Download (.pdf)
Table 68–1. Autoantibodies and Other Assays Appropriate to the Evaluation of Sensorineural Hearing Loss.
- Anti-nuclear antibody
- Anti-Ro antibody
- Anti-La antibody
- dsDNA antibody
- Serum C3 and C4
- Antineutrophil cytoplasmic antibody (ANCA)
- Lyme serology
- Antibodies to HSP-70 (68-kD antigen)
- Routine blood and urine tests to exclude signs of systemic disease: complete blood count, serum chemistries, urinalysis with microscopy
Magnetic resonance imaging studies are essential to exclude tumors of the cerebellopontine angle.
Audiogram and Electronystagmogram
Formal hearing tests should be performed on any patient with a complaint of hearing loss. The audiogram (Figure 68–2A) is a graphic representation of the lowest volume at which individual tones ranging from 250 Hz to 8000 Hz can be distinguished. An audiogram from a patient with classic SNHL is depicted in Figure 68–2B. The reception threshold measures the lowest volume at which speech is heard. The discrimination score measures the ability to discriminate words. Electronystagmography measures ocular movement in response to various stimuli, including warm and cold caloric stimulation of the ears. This test assesses the functional strength and symmetry of the VORs in response to input from both ears. Audiometry and electronystagmography testing may confirm clinical impressions of inner ear dysfunction and quantify the degree of organ involvement.
Audiogram. A: Normal bilateral hearing. B: Symmetric high-frequency hearing loss in a patient with IMIED. Bone conduction thresholds (R = [and L = ]) are measures of auditory function of the cochlea and proximal neural pathway, whereas air conduction thresholds (R = circle, L = X) measure function of the entire auditory system. SRT, speech reception threshold; SDS, speech discrimination score. (© 2000 Lippincott Williams & Wilkins.)
Serologic Testing for Antibodies to the 68 kD Antigen
The impact of early diagnosis and treatment on long-term hearing prognosis in patients with IMIED has prompted the search for specific markers of inner ear inflammation. The sera of patients with rapidly progressive bilateral SNHL contain antibodies that react with a variety of antigens from human and bovine inner ears. However, antibodies to cochlear-specific antigens have low specificities for rapidly progressive SNHL. In contrast, antibodies to a non-organ specific protein, a 68-kD antigen found in the inner ear, kidney, brain, and other organs of non-human species (eg, cows), appear to have relatively high specificity for IMIED in humans. In a group of 72 patients with rapidly progressive bilateral SNHL, investigators found that 58% of participants possessed antibodies to the 68-kD antigen, compared to only 2% of normal participants and none of the participants with otosclerosis or Cogan syndrome (P <.01). This test may therefore be useful in helping establish the diagnosis of IMIED if the clinical scenario is compatible, but the test characteristics (sensitivity, specificity, positive, and negative predictive values) remain to be established firmly in the context of day-to-day practice.