What are the diagnostic criteria for Idiopathic Intracranial Hypertension (IIH)?

Diagnostic Criteria for Idiopathic Intracranial Hypertension

IIH is diagnosed when a patient has papilledema (or sixth nerve palsy in rare cases without papilledema), elevated lumbar puncture opening pressure (>250 mm CSF in non-obese adults, >280 mm CSF in obese adults or children), normal neuroimaging excluding mass lesions or venous sinus thrombosis, and normal CSF composition. 1, 2, 3

Required Diagnostic Components

Neuroimaging (Mandatory First Step)

• Urgent MRI brain within 24 hours is the preferred initial test; if unavailable, perform urgent CT brain followed by MRI when available 1, 2
• CT or MR venography is mandatory within 24 hours to exclude cerebral sinus thrombosis 1, 2
• Imaging must show no evidence of hydrocephalus, mass, structural or vascular lesion, and no abnormal meningeal enhancement 1, 2, 3

Clinical Examination Findings

• Papilledema must be documented as the hallmark finding 2
• Cranial nerve examination should reveal no abnormalities except possible sixth nerve palsy/palsies; if other cranial nerves are involved, consider alternative diagnoses 1, 2
• Blood pressure measurement is mandatory to exclude malignant hypertension (diastolic BP >120 mmHg) 1, 3

Lumbar Puncture Requirements

• Following normal imaging, all patients with papilledema require lumbar puncture 1
• Opening pressure must be elevated: >250 mm CSF in non-obese, non-sedated adults; >280 mm CSF in obese adults or children 3, 4
• CSF composition must be normal (no infection, malignancy, or other abnormalities) 3

Supportive MRI Signs (Not Required but Helpful)

While not mandatory for diagnosis, the following neuroimaging findings support IIH when present 3, 5:

• Posterior globe flattening (67.1% sensitivity in IIH vs 11.1% in non-IIH) 6, 5
• Perioptic nerve sheath distension (69.8% vs 29.3%) 6, 5
• Optic nerve disc protrusion 5
• Transverse sinus stenosis (60.2% vs 18.9%) 6, 5
• Empty sella 3
• Moderate suprasellar herniation (71.4% vs 47.4%) 6

Recent evidence suggests that ≥3 neuroimaging signs have 59.5% sensitivity and 93.5% specificity for IIH, and some experts propose diagnosis can be made with 2 out of 3 objective findings: papilledema, elevated opening pressure, and ≥3 neuroimaging signs 6

Special Diagnostic Subtypes

IIH Without Papilledema (Rare)

• Meets all diagnostic criteria except papilledema is absent 1, 2
• This is an uncommon variant requiring careful consideration 2
• Some cases with normal CSF pressure but papilledema and IIH symptoms may still respond to acetazolamide, though this remains controversial 7

Typical vs Atypical IIH

• Typical IIH: Female, childbearing age, BMI >30 kg/m² 1, 2, 8
• Atypical IIH: Not female, not childbearing age, or BMI <30 kg/m² - requires more extensive investigation to exclude secondary causes 1, 8

Fulminant IIH

• Defined as precipitous decline in visual function within 4 weeks of diagnosis 1, 8
• Requires urgent surgical intervention 8

Common Presenting Symptoms (Not Diagnostic Criteria)

While these symptoms prompt investigation, none are pathognomonic for IIH 2:

• Headache (92% of patients) - progressively severe and frequent, highly variable phenotype 2, 8
• Transient visual obscurations (seconds-long darkening of vision) 2
• Pulsatile tinnitus 2
• Visual blurring 2
• Horizontal diplopia 2

Critical Diagnostic Pitfalls

• Do not diagnose IIH if other cranial nerves beyond the sixth are involved - this suggests alternative pathology 1, 2
• Atypical patients (male, normal weight, outside childbearing age) require more thorough investigation for secondary causes 1, 8
• Venography is not optional - missing venous sinus thrombosis is a critical error 1, 2
• Headache phenotype can mimic primary headache disorders, making clinical diagnosis challenging 2
• If diagnostic uncertainty exists regarding papilledema, consult an experienced clinician before performing invasive tests 1