What is the most likely diagnosis for a patient with a single sudden‑onset vertigo attack that is most severe in the first 1‑3 days and then gradually resolves over 4‑6 weeks?

Vestibular Neuronitis (Vestibular Neuritis)

The clinical presentation described—a single sudden-onset vertigo attack most severe in the first 1-3 days with gradual resolution over 4-6 weeks—is classic for vestibular neuronitis, a peripheral vestibular disorder that represents one of the two main causes of acute vestibular syndrome (AVS) along with cerebellar/brainstem stroke.

Diagnostic Framework

This presentation fits the acute vestibular syndrome (AVS) pattern, defined as acute-onset prolonged vertigo/dizziness with accompanying gait imbalance, motion intolerance, nausea/vomiting, with or without nystagmus 1, 2. The key distinguishing feature is the timing: a single continuous episode lasting days to weeks, not brief triggered episodes or recurrent attacks 3, 1.

Clinical Characteristics of Vestibular Neuronitis

The diagnosis is supported by:

• Sudden onset of severe rotatory vertigo with nausea and vomiting
• No hearing loss at onset (distinguishes from labyrinthitis)
• Peak severity in first 1-3 days with prominent symptoms gradually lessening during the first week
• Most patients return to work after one month, though complete recovery takes 4-6 weeks 4
• Spontaneous nystagmus beating away from the affected side
• Abnormal vestibulospinal tests (Romberg, gait disturbance)
• Totally extinguished or severely reduced caloric responses on the affected side 4

Critical Differential: Stroke vs. Vestibular Neuronitis

The most important clinical decision is distinguishing vestibular neuronitis from cerebellar or brainstem infarction, as approximately 4-15% of patients presenting with AVS have stroke 5. This distinction cannot be made reliably by symptom quality alone.

The Head Impulse Test is Essential

Mastery of the head impulse test is required to distinguish between vestibular neuronitis and cerebellar infarction 3. In vestibular neuronitis:

• Head impulse test is abnormal (positive corrective saccade toward the affected side)
• In stroke, the head impulse test is typically normal despite severe vertigo

The HINTS examination (Head Impulse, Nystagmus, Test of Skew) provides superior diagnostic accuracy compared to early MRI, which has a false-negative rate up to 50% for acute posterior circulation strokes 5.

Etiology and Predisposing Factors

While the exact cause remains unclear, viral infection is suspected:

• 27-37% of patients report a recent respiratory infection 4
• Serological and hematological evidence of viral infection found in approximately 18% of cases 4
• The condition does not appear related to hypertension or other vascular risk factors in typical cases 4

Prognosis

The prognosis is excellent 4. The natural history follows the timeline described in your question precisely, with most functional recovery within 4-6 weeks, though subtle vestibular deficits may persist longer.

Common Pitfalls to Avoid

• Do not rely on MRI alone in the acute setting—small strokes are frequently missed, especially within the first 24-48 hours 5
• Do not assume peripheral cause based on severe vertigo alone—stroke can present identically
• Do not overlook the head impulse test—it is more sensitive than early MRI for stroke detection in AVS
• Do not diagnose vestibular neuronitis if hearing loss is present—consider labyrinthitis or other diagnoses
• Do not confuse with BPPV—BPPV causes brief triggered episodes (seconds), not continuous days-long vertigo 3, 1