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Introduction

Labyrinthitis is self-limiting inner ear disorder, often secondary to viral infection. The infection of vestibular neuron and labyrinth primary affects balance and hearing. The condition is commonly called as vestibular neuritis/ vestibular neuronitis.

Classification

Labyrinthitis may be classified according to etiology into 5 groups:

• Tympanogenic
• Post-traumatic
• Meningogenic
• Hematogenic
• Autoimmune

Pathophysiology

• The major cause for labyrinthitis is known to be viral infection or post-viral inflammatory disorder that mainly affects the vestibular portion of eighth cranial nerve.
• The exact cause of labyrinthitis or vestibular neuronitis is still not clear.
• MRI with contrast had shown enhancement of the vestibular nerve fibers within the internal auditory canal, suggesting inflammatory process.

Causes

Labyrinthitis may be caused by viral infection, bacterial infection of inner ear, or ototoxic drugs.

Differential Diagnosis

Labyrinthitis must be differentiated from other diseases that cause vertigo along with gait impairment such as:

Disease/Variable	Presentation	Causes	Risk factors	Imaging
Brainstem infarction	Neurological sign and symptoms such as hemiplegia, cranial nerve deficits, ataxia may be present in brainstem infarction (vs labyrinthitis- no any neurological deficits in labyrinthitis) Sustained dizziness and vertigo observed in brainstem infarction.	Occlusion of the blood vessels supplying to brainstem ( vs labyrinthitis- secondary to viral infection/idiopathic)	Hypertension and cardio-aortic diseases are found in the majority of patients with cerebellar infarction	Brain stem infarction can reliably be visualized by a combination of DW-MRI and T2-weighted images beginning 12 hours after the ischemic attack( vs labyrinthitis- brainstem is normal in imaging studies)
Cerebellar Stroke	Frequently present with sudden headache, nausea and vomiting, dizziness, and a striking difficulty walking and loss of consciousness in most cases.	Usually caused by a blood clot that obstructs blood flow to the cerebellum.	Hypertension, small vessel disease and old ages are common risk factors for cerebellar stroke.	Cerebellar stroke can be diagnosed earlier by MRI and CT scanning.

Risk Factors

There are no established risk factors for labyrinthitis. However, viral infection, allergies or ototoxic drugs may be responsible for development of labyrinthitis in some cases.

Natural History, Complications and Prognosis

Labyrinthitis is self limiting disorder, often becomes acutely symptomatic for 1 to 2 days. The symptoms gradually improve over 2 weeks. Recurrence is rare. If left untreated, 15% of patients with labyrinthitis may progress to develop Benign Paroxysmal Positional Vertigo (BPPV) and around 10% may progress to develop panic disorder over 2 years.

Diagnosis

The diagnosis of labyrinthitis is based on clinical evaluation, rather than any test. The viral of preceding viral illness and acute onset symptoms like dizziness,nausea and vomiting with gait impairment suggestive of labyrinthitis. No any specific diagnostic test are available.

Diagnostic Study of Choice

Neuroimaging, generally MRI is done to rule out other acute causes for symptoms that includes cerebellar hemorrhage and brainstem infraction. If MRI not available, CT scan can be done to look for alternative diagnosis.

History and Symptoms

The hallmark feature of labyrinthitis is sudden onset severe vertigo. A positive history of preceding viral infection and vertigo with gait instability is suggestive of labyrinthitis. The common symptoms of labyrinthitis include dizziness, gait abnormality, nausea and vomiting.

Physical Examination

Common physical examination findings of labyrinthitis include nystagmus (unilateral-horizontal mostly), positive head impulse test(unable to maintain visual fixation on rapid turning of head towards the side of lesion), gait instability( tends to fall on side of lesion) and absence of neurological sign and symptoms. Unilateral hearing loss might be present in some cases.

Laboratory Findings

There are no diagnostic laboratory findings associated with labyrinthitis.

CT scan

There are no CT scan findings associated with labyrinthitis. However, a CT scan may be helpful to rule out differential diagnosis like cerebellar hemorrhage/infarction and brainstem infarction.

MRI with contrast

MRI of inner ear may be helpful in the diagnosis of labyrinthitis. Findings on MRI suggestive of labyrinthitis include abnormal enhancement in membranous labyrinth on post-contrast T1WI scan.

Treatment

The majority of cases of labyrinthitis are self-limited and require only supportive care during acute symptoms.

Supportive therapy for labyrinthitis includes anti-emetics, anti-histamines, anti-cholinergics and benzodiazepines. Glucocorticoids and anti-viral drugs are the mainstay of treatment for labyrinthitis. Vestibular rehabilitation therapy also recommended among all patients who develop labyrinthitis.