Vestibular Neuronitis

Etiology

Vestibular neuritis is believed to be an inflammatory disorder selectively affecting the vestibular portion of the eighth cranial nerve. The cause is presumed to be of viral origin.[2]

Epidemiology

The data is lacking regarding the incidence of acute vestibular neuritis, but it is known to be the third most common cause of peripheral vertigo following BPPV and Meniere disease. Estimates are that acute vestibular neuritis or labyrinthitis gets diagnosed in 6% of patients who present to emergency departments in the USA the complaint of dizziness. This stat is likely an under-representation of its true incidence as another 22% of the patients complaining of dizziness are discharged without anything more specific than “dizziness” or “vertigo.” A portion of these non-specific diagnoses likely includes actual cases of acute vestibular neuritis.[1] It has no gender preference and usually affects those in their middle ages. 

Pathophysiology

Vestibular neuritis is believed to be an inflammatory disorder selectively affecting the vestibular portion of the 8th cranial nerve. The cause is presumed to be of viral origin (e.g., the reactivation of latent HSV infection), but other causes of vascular etiology and immunologic in origin are proposals. Vestibular damage appears to have a predilection for the superior portion of the vestibular labyrinth (supplied by the superior division of the vestibular nerve) over the inferior aspect of the vestibular labyrinth (supplied by the inferior portion of the vestibular nerve). The underlying mechanism is unclear, but this phenomenon may be explainable by anatomical differences between the two vestibular divisions.[3]

History and Physical

The typical presentation of vestibular neuritis is usually with the acute onset of the following:

• Vertigo
• Nausea
• Vomiting
• Balance problems

The symptoms in vestibular neuritis are typically constant, in contrast to the episodic symptoms of other peripheral causes such as BPPV or Meniere's disease. Symptoms are worsened with head movement but not triggered. Symptoms generally develop over several hours, peak within the first 24 to 48 hours, and typically last several days before resolving without intervention. Patients will likely note a preceding or concurrent viral illness, but it is important to note that the lack of this history does not rule out the disease as it is reported to be absent in up to 50% of patients [2].

Other symptoms, such as headaches, are usually absent. It is vital to ask the patient about accompanying symptoms that may suggest central disorders of vertigo, such as visual changes, somatosensory changes, weakness, dysarthria, incoordination, or an inability to walk. If any of these are present, one must broaden the differential with to central causes of vertigo. When the additional symptom of unilateral hearing loss is present, this shifts the diagnosis towards labyrinthitis [2]. When attempting to differentiate this associated hearing change from Meniere disease, it is important to know that Meniere disease also presents with vestibular and auditory dysfunction. Still, patients with Meniere have more episodic and not continuous symptoms lasting 20 minutes to usually no more than 12 hours.[3]

Physical Exam

Patients presenting with vestibular neuritis will have a normal physical exam and neurological exam. The clinician needs to look for clues that might point to a central cause of vertigo, warranting a more thorough evaluation. Central causes of vertigo are usually continuous symptoms along with truncal instability, an unsteady gait, dysarthria, and other focal neurological symptoms. Symptoms that are episodic in nature point to the more common other peripheral causes like BPPV and Meniere’s disease. Other findings that are consistent with peripheral causes of vertigo, like vestibular neuritis, include a negative HINTs exam. The HINTS examination (see figure 1) consists of three components: Head Impulse, Nystagmus, and Test of Skew. It has been found to have high sensitivity and specificity (100% and 96%) for distinguishing peripheral from central vertigo in patients presenting with acute vestibular syndrome when performed correctly by the experienced clinician.[1][2][4] Videos of this exam are available online. The following components make up this exam are described as follows:

• The head impulse is performed with the patient sitting facing the examiner. Head positioning is at about 20 degrees to the left and right from midline, and then the examiner will briskly turn the head toward the midline. The examiner will then check to see whether or not the patient can maintain visual fixation on the examiner. If the patient’s eyes are not able to fixate on the examiner during the maneuver, their eyes will be noted to saccade back toward the midline. When the saccade is present, the test is considered a positive test and points towards a peripheral etiology such as vestibular neuritis. If there is a corrective saccade in both directions, this is worrisome for a central pathology. When the patient can fixate on the examiner’s nose during the entire maneuver, the test is considered negative and points towards a central etiology.
• Nystagmus is another exam tool that is a part of the HINTS exam. It is important to note that the naming of nystagmus is for the direction of the fast component. Nystagmus follows a rule termed Alexander’s law, which states that the intensity of nystagmus increases when the patient looks towards the direction of the fast phase. The slow phase of the nystagmus beats towards the injured side. Spontaneous nystagmus (when a patient is looking straight ahead without fixation) is determined to be negative (peripheral) if it is described as horizontal beating or horizontal-torsional and is unidirectional (fast phase beats towards one direction regardless of the orientation of gaze, patient looking left or right). Vertigo that is observed to be vertical and or bidirectional is considered a positive finding and points to a central etiology.
• The test of skew is performed with the patient facing the examiner. The examiner then covers and uncovers the patient's eye one at a time with his hand while the patient attempts to fixate on the examiner.  Any deviation of one eye while it is covered, followed by correction after uncovering the eye, is considered a positive or abnormal test pointing to a central etiology. The patient with vestibular neuritis should be able to maintain symmetrical eye alignment without deviation during the entire exam.

Other neurologic signs and symptoms: dysarthria, dysphagia, facial droop, dysmetria, motor weakness, sensory loss, and abnormal reflexes are typically absent.[1][2] The auditory function in patients with vestibular neuritis is usually preserved, but when there is combined unilateral hearing loss, it is called labyrinthitis. It is crucial to assess the patient's gait and posture as it can help localize the affected ear or be a signal of a more grave diagnosis. Their seated posture should be normal, and while their gait is usually unaffected, they will tend to veer or fall toward the affected side (opposite to nystagmus fast phase). 

Evaluation

The diagnostic basis is mostly on key signs and symptoms of acute vestibular dysfunction, as mentioned above. However, because vestibular neuritis is a diagnosis of exclusion, the main focus in patients presenting with acute spontaneous vertigo is to rule out a stroke or other central causes. 

Neuroimaging of the brain with MRI or CT imaging is not indicated in most cases but can be helpful when exam findings of a peripheral lesion are inconsistent if risk factors for stroke exist and symptoms do not show improvement within 48 hours.[5] If a rule test is needed, an MRI of the brain is more sensitive than a CT scan to rule out a CVA.

Other tests like cervical and ocular vestibular evoked myogenic potentials along with video head impulse testing have made it possible to determine which vestibular division is involved in vestibular neuritis.[6][7]

Treatment / Management

The treatment of vestibular neuritis usually consists of acute symptomatic treatment with medications such as antiemetics (promethazine, metoclopramide), antihistamines (diphenhydramine, meclizine), and benzodiazepines (diazepam, lorazepam). Following the acute phase, other therapies, such as vestibular rehabilitation, are often recommendations.[8] The utilization of the above antiemetics, antihistamines, and benzodiazepines should be used for no more than three days or so as these medications can delay central compensation and lead to chronic problems and recurrent vertigo.[3][8]   (B3)

In the past, the use of corticosteroids has been a therapeutic option, but their efficacy remains controversial. This therapy was studied in a 2011 Cochrane review, which found insufficient evidence to recommend their use in those with acute vestibular dysfunction.[9](A1)

The viral etiology hypothesis has led to the theoretical benefit from antiviral medications; however, the use of valacyclovir either alone or combined with a glucocorticoid has not been shown to be effective.[10](B3)

Differential Diagnosis

The differential diagnosis in patients presenting with vertigo can be broken down to that of peripheral or central etiologies as well as those with or without hearing loss:

Peripheral Causes:

• Benign paroxysmal positional vertigo (BPPV): Presents with episodic vertigo following predictable head movements that trigger symptoms. It is usually an acute onset with a duration of seconds to minutes. 
• Meniere disease: Presents acutely with recurrent episodes of vertigo along with sensory symptoms (e.g., ear fullness, tinnitus, low-frequency hearing loss). Symptoms last minutes to hours. 
• Labyrinthitis: Presents with similar symptoms to vestibular neuritis but will also include auditory symptoms such as unilateral hearing loss. Symptom duration lasts days to weeks.[2]

Central Causes:

• Vestibular migraine: Can present with central or peripheral signs/symptoms. Patients will have a headache and will note recurrent episodes and must have a documented diagnosis of migraine. Symptoms duration is minutes to hours. 
• Vertebrobasilar TIA: Patients will usually have vascular risk factors. Symptoms are shorter and of acute onset. Symptoms duration is minutes to hours
• Brainstem ischemia/infarct: Patients will often have vascular risk factors or a history of trauma. There is commonly noted to be a constellation of neurological symptoms along with vertigo present, known as a Wallenberg syndrome, which is an infarct of the lateral medulla. The onset is acute, and the duration of symptoms is days to weeks.
• Cerebellar infarct or hemorrhage - There are usually vascular risk factors or trauma present. Symptom onset is acute, and the duration is days to weeks.[2] There are typically associated neurological deficits present along with an abnormal HINTS exam, truncal instability, headache, ipsilateral Horner syndrome, limb ataxia, abnormal pupillary response, and other neurological abnormalities.

Hearing Loss Present: 

• Perilymphatic fistula
• Cholesteatoma
• Meniere disease
• Labyrinthitis
• Acoustic neuroma
• Autoimmune processes
• Psychogenic

Hearing Loss Absent:

• Benign positional paroxysmal vertigo
• Vertebral basilar insufficiency
• Migraines
• Vestibulopathy
• Vestibular neuronitis
• Central nervous system disorders
• Lyme disease
• Multiple sclerosis

Prognosis

The natural history of this disease is uncomplicated with complete resolution in most cases. Some can have incomplete resolution and with a study showing 15% with persistent symptoms at one year.[2] Recurrence of vestibular neuritis is infrequent, with studies that have shown its recurrence in only 2 to 11% of patients.[11][12]

Complications

Two important complications associated with vestibular neuritis are benign paroxysmal positional vertigo (BPPV) and persistent postural-perceptual dizziness (PPPD), a relatively new term. Research has found that 10 to 15% of patients with vestibular neuritis will develop BPPV in the affected ear within a few weeks.[11][12] PPPD is a new diagnostic syndrome of non-spinning vertigo and unsteadiness, which combines significant features of chronic subjective dizziness, phobic postural vertigo, and other related disorders.[13] One study found PPPD in 25% of patients who were followed 3 to 12 months after acute or episodic vestibular disorders.[14]