How to differentiate between vestibular migraine and idiopathic intracranial hypertension (IH) in a patient with episodic symptoms not responding to gabapentin?

Differentiating Vestibular Migraine from Idiopathic Intracranial Hypertension

You are correct that the episodic nature of symptoms strongly favors vestibular migraine over IIH, as IIH characteristically presents with persistent daily headache rather than episodic attacks. 1

Key Distinguishing Features

Temporal Pattern (Most Critical Differentiator)

Vestibular migraine is fundamentally episodic:

• Requires ≥5 episodes of vestibular symptoms lasting 5 minutes to 72 hours 2, 1
• Episodes are discrete with symptom-free intervals between attacks 2
• Symptoms may evolve from episodic to chronic over an average of 7 years, but this is the exception rather than the rule 3

IIH presents with persistent symptoms:

• Persistent daily headache is the hallmark presentation 1
• 68% experience migrainous-type headaches, but these are continuous, not episodic 1
• Vestibular symptoms (dizziness, unsteadiness) when present are typically constant, not episodic 4

Physical Examination Findings

Fundoscopic examination is the critical next step:

• Papilledema is present in classic IIH and is a hallmark finding 1
• Absence of papilledema essentially rules out classic IIH (though IIHWOP exists, it's rare) 5
• This single examination can immediately differentiate the two conditions 1

Additional IIH-specific findings:

• Optic nerve sheath distention on imaging 6
• Flattened posterior globe 6
• Decreased pituitary gland height 6

Associated Symptoms

IIH-specific symptoms that distinguish it from vestibular migraine:

• Pulsatile tinnitus (low-pitch, synchronous with heartbeat) 7, 4
• Transient visual obscurations (brief episodes of vision loss with postural changes) 7
• Radicular neck pain 7
• Head fullness-pressure sensation that is constant 4

Vestibular migraine features:

• Migrainous features (photophobia, phonophobia, visual aura) present in ≥50% of episodes 2, 1
• Symptoms triggered by typical migraine triggers 3
• Concomitant headache occurs in only 48% of episodes 3

Diagnostic Algorithm for Your Patient

Step 1: Confirm Episode Pattern

• Document whether symptoms are truly episodic (discrete attacks with complete resolution) or persistent with fluctuations 1
• If episodic with 5-72 hour duration: strongly favors vestibular migraine 2
• If persistent daily symptoms: consider IIH 1

Step 2: Perform Fundoscopic Examination

• Presence of papilledema: IIH until proven otherwise 1
• Absence of papilledema: IIH highly unlikely 1

Step 3: Assess for IIH-Specific Symptoms

• Pulsatile tinnitus present: increases IIH likelihood 7, 4
• Transient visual obscurations: specific for IIH 7
• These symptoms are not features of vestibular migraine 2

Step 4: Consider Neuroimaging if Red Flags Present

Indications for MRI with venography:

• Papilledema on examination 1
• Severe persistent headache with visual symptoms 1
• Failure to respond to appropriate treatment 1
• Atypical presentation that doesn't fit vestibular migraine criteria 1

Expected MRI findings in IIH:

• Partially empty sella 4, 6
• Bilateral transverse sinus stenosis 6
• Optic nerve sheath distention 6
• Flattened posterior globe 6

Step 5: Lumbar Puncture if IIH Suspected

• Opening pressure >25 cm H₂O confirms IIH 1
• Normal CSF chemistry and microscopy 4
• Symptom improvement after pressure reduction supports diagnosis 4, 5

Common Pitfalls to Avoid

Do not be misled by overlapping features:

• IIH patients can have migrainous-type headaches (68% do), but these are persistent, not episodic 1
• Both conditions can cause dizziness, but the pattern differs: episodic in vestibular migraine vs. constant in IIH 4, 3
• Some IIH patients develop endolymphatic hydrops symptoms that may appear episodic, but the underlying headache remains constant 5

Gabapentin failure does not differentiate these conditions:

• Neither vestibular migraine nor IIH has gabapentin as a first-line treatment
• Treatment failure should prompt diagnostic reconsideration, not assumption of alternative diagnosis 1

The presence of vestibular symptoms does not exclude IIH:

• 77.4% of IIH patients report dizziness 5
• 22.6% report vertigo 5
• However, these symptoms in IIH are typically constant, not episodic 4

Your Clinical Reasoning is Sound

Your observation about episodic vs. constant symptoms is the most important clinical distinction. 1 If your patient has discrete episodes lasting 5 minutes to 72 hours with complete resolution between attacks, this pattern is incompatible with typical IIH presentation and strongly supports vestibular migraine. 2, 1 The next essential step is fundoscopic examination to definitively exclude IIH. 1