What is the precise definition of isolated vertigo, and does a patient who has vertigo with gait instability still qualify as having isolated vertigo?

Definition of Isolated Vertigo and Gait Instability

Isolated vertigo (or isolated acute vestibular syndrome, AVS) is defined as acute-onset continuous vertigo with nystagmus, gait instability, nausea/vomiting, and motion intolerance that persists for at least 24 hours WITHOUT focal neurological deficits—and yes, gait instability is an expected component of isolated AVS, not an exclusion criterion. 1

Core Definition of Isolated AVS

The term "isolated" refers to the absence of additional focal neurological signs (such as dysarthria, dysmetria, dysphagia, sensory/motor deficits, or Horner's syndrome), not the absence of gait disturbance. 2 The key components include:

• Acute-onset continuous vertigo lasting ≥24 hours 1
• Nystagmus (spontaneous) 1
• Gait instability and postural unsteadiness 3
• Nausea/vomiting and motion intolerance 1
• No other focal neurological deficits 1

Why Gait Instability Is Part of Isolated AVS

Gait instability is an intrinsic feature of AVS, whether peripheral or central in origin. 3 In fact, approximately 11% of patients with isolated cerebellar infarction present with isolated vertigo, nystagmus, and postural unsteadiness that mimics acute peripheral vestibular disorders. 3

• Patients with isolated AVS routinely demonstrate truncal ataxia and inability to walk without support during the acute phase 4
• The presence of gait instability alone does not indicate a central (stroke) etiology 3
• What matters diagnostically is whether there are additional focal neurological signs beyond the expected vestibular triad of vertigo, nystagmus, and ataxia 1

Critical Diagnostic Pitfall: Ataxia Without Nystagmus

A crucial caveat: isolated truncal ataxia WITHOUT nystagmus should raise suspicion for central pathology. 5 In a multicenter study, 15% of patients with acute vertigo presented with acute truncal ataxia in the absence of nystagmus, and these cases included posterior circulation strokes, multiple sclerosis, and cerebellar tumors. 5 This represents a diagnostic blind spot where standard HINTS examination may not be applicable. 5

Epidemiology and Risk Stratification

The differential diagnosis of isolated AVS depends heavily on vascular risk factors:

• Most commonly benign peripheral causes (vestibular neuritis, labyrinthitis) in low-risk patients 1
• 25% have posterior circulation infarcts in general ED populations with AVS 2
• Up to 75% have strokes in high vascular-risk cohorts 2
• 65-80% of stroke-related AVS cases lack focal neurological deficits, making them clinically indistinguishable from peripheral causes without specialized examination 2

Bedside Examination: The HINTS Protocol

When performed by trained clinicians, the HINTS examination achieves 100% sensitivity for detecting central (stroke) causes, superior to the 46% sensitivity of early MRI. 2 The three components are:

• Head Impulse Test: Normal (corrective saccades absent) suggests central cause 2
• Nystagmus: Direction-changing or gaze-evoked suggests central cause 2
• Test of Skew: Vertical misalignment (skew deviation) suggests central cause 2

Red flags for central vertigo include:

• Direction-changing nystagmus without head position change 2
• Downbeat nystagmus on Dix-Hallpike without torsional component 2
• Gaze-evoked or direction-switching nystagmus 2
• Normal head impulse test in the setting of acute continuous vertigo 2

Clinical Algorithm for Isolated AVS

Step 1: Confirm AVS criteria (acute continuous vertigo ≥24 hours with nystagmus, gait instability, nausea/vomiting) 1, 6

Step 2: Assess for focal neurological deficits beyond the vestibular triad 1

• If present → NOT isolated AVS, image immediately 1
• If absent → proceed to Step 3

Step 3: Check for ataxia-without-nystagmus pattern 5

• If truncal ataxia present but nystagmus absent → high suspicion for central cause, image immediately 5
• If both present → proceed to Step 4

Step 4: Perform HINTS examination (if trained examiner available) 2

• If any component suggests central cause → image for stroke 2
• If all three components suggest peripheral cause AND low vascular risk → imaging may not be required 1
• If HINTS suggests peripheral but high vascular risk factors present → consider imaging (11% stroke rate even without focal deficits) 1

Step 5: Risk stratification 1

• High vascular risk (age >50, hypertension, diabetes, atrial fibrillation, prior stroke) → lower threshold for neuroimaging 1
• Low vascular risk with reassuring HINTS → may manage as peripheral vestibular disorder 1

Imaging Considerations

Isolated AVS without features of central vertigo does not require routine imaging if expert HINTS examination is negative. 1 However:

• Non-contrast head CT detects acute infarct in up to 11% of isolated AVS cases 1
• MRI with diffusion-weighted imaging is more sensitive than CT but still misses 54% of strokes in the first 24-48 hours 2
• Clinical examination by trained providers outperforms early MRI for detecting vascular vertigo 3