Approach Considerations
No specific laboratory studies are available for labyrinthitis. Routine serology testing often fails to reveal an infectious organism, and when results are positive, methods to determine if the same organism caused the damage to the membranous labyrinth are not available. Obtain appropriate tests to help exclude other possible etiologies in the differential diagnosis.
Examine cerebrospinal fluid if meningitis is suggested. If a systemic infection is considered, a complete blood count (CBC) and blood cultures are indicated. Perform culture and sensitivity testing of middle ear effusions, if present, and select appropriate antibiotic therapy accordingly.
Currently, no accurate or reliable autoimmune test is commercially available for autoimmune labyrinthitis. The diagnosis of the condition rests on a positive clinical response to steroid therapy. [19]
Imaging Studies
CT scanning
Consider a computed tomography (CT) scan prior to lumbar puncture in cases of possible meningitis. A CT scan is also useful to help rule out mastoiditis as a potential cause. A temporal bone CT scan may aid in the management of patients with cholesteatoma and labyrinthitis.
A noncontrast CT scan is best for visualizing fibrosis and calcification of the membranous labyrinth in persons with chronic labyrinthitis or labyrinthitis ossificans.
MRI
Magnetic resonance imaging (MRI) can be used to help rule out acoustic neuroma, stroke, brain abscess, or epidural hematoma as potential causes of vertigo and hearing loss.
The cochlea, vestibule, and semicircular canals enhance on T1-weighted, postcontrast images in persons with acute and subacute labyrinthitis. [20] This finding is highly specific and correlates with objective and subjective patient assessment. Improvements that have been made in MRI techniques may make this the study of choice for suspected labyrinthitis. [21] The intensity of gadolinium enhancement on MRI can be useful in distinguishing intracochlear tumors from other inner ear pathology, including labyrinthitis. [22]
Audiography
Obtain an audiogram in all patients who may have labyrinthitis. Evaluate critically ill and severely vertiginous patients when they are stable and able to tolerate the test. The audiogram may show different findings in relation to the etiology of the labyrinthine inflammation. For example, a patient with otitis media-induced labyrinthitis would most likely have a mixed hearing loss, whereas viral labyrinthitis would present with a sensorineural hearing loss. Otoacoustic emission (OAE) testing or auditory brainstem response (ABR) testing may be helpful in patients who are unable to cooperate for standard audiometry.
Persons with viral labyrinthitis have mild to moderate, high-frequency SNHL in the affected ear, although any frequency spectrum may be affected.
Suppurative (bacterial) labyrinthitis typically results in severe to profound, unilateral hearing loss. In cases of meningitis, the loss is often bilateral. Persons with serous (bacterial) labyrinthitis have unilateral, high-frequency hearing loss in the affected ear. A conductive loss in the same ear may occur secondary to effusion.
Vestibular Testing
Caloric testing and an electronystagmogram may help in diagnosing difficult cases and establishing a prognosis for recovery. Evidence suggests that careful evaluation of the vestibulo-ocular reflex may help to establish the etiology of the labyrinthitis. [23]
Persons with viral labyrinthitis have nystagmus with unilateral caloric vestibular paresis/hypofunction.
Persons with suppurative (bacterial) labyrinthitis have nystagmus and an absent caloric response on the affected side.
Persons with serous (bacterial) labyrinthitis usually have normal electronystagmogram results, but they may have a decreased caloric response in the affected ear. However, the presence of a middle ear effusion can attenuate the caloric response and cause a false-positive finding.
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Anatomy of the labyrinth.
