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

Clinical Criteria for Diagnosing Idiopathic Intracranial Hypertension (IIH)

The diagnosis of IIH requires evidence of raised intracranial pressure with normal neuroimaging, normal CSF composition, and no other identified cause of intracranial hypertension. 1, 2

Diagnostic Approach

• Urgent MRI brain within 24 hours is required; if unavailable within this timeframe, urgent CT brain should be performed with subsequent MRI 2
• MRI/CT should show no evidence of hydrocephalus, mass, structural or vascular lesion, and no abnormal meningeal enhancement 1, 2
• CT or MR venography is mandatory to exclude cerebral sinus thrombosis within 24 hours 1, 2
• Lumbar puncture with opening pressure measurement is essential after normal neuroimaging 1
• Opening pressure should be measured in the lateral decubitus position and be elevated (typically >250 mm CSF in adults) 1, 3
• CSF composition must be normal 2, 3

Clinical Features

• Papilledema is the hallmark finding in most IIH cases 2, 3
• Headache is the most common presenting symptom, typically progressively more severe and frequent 2
• Other common symptoms include:
  • Transient visual obscurations (brief episodes of vision darkening) 2
  • Pulsatile tinnitus (whooshing sound in ears) 2
  • Visual blurring 2
  • Horizontal diplopia (often due to sixth nerve palsy) 1, 2

Neurological Examination

• Cranial nerve examination should be performed; typically, there should be no cranial nerve involvement other than possible sixth nerve palsy 1, 2
• If other cranial nerves or pathological findings are involved, alternative diagnoses should be considered 1

Patient Demographics

• Typical IIH patients are female, of childbearing age, with BMI >30 kg/m² 1, 2, 3
• Atypical IIH patients (males, non-reproductive age, BMI <30 kg/m²) require more in-depth investigation 1, 2

Neuroimaging Findings

• While neuroimaging should be normal to exclude secondary causes, certain radiological signs may support the diagnosis of IIH 3:
  • Empty or partially empty sella 3, 4
  • Distension of perioptic subarachnoid space 3, 4
  • Flattening of the posterior sclera/globe 3, 4, 5
  • Intraocular protrusion of the optic papilla 4
  • Transverse sinus stenosis 3, 5
• Recent evidence suggests that ≥3 neuroimaging signs has a specificity of 93.5% for IIH 5

Diagnostic Classification

• Definite IIH: Meets all criteria including papilledema and elevated opening pressure 1, 2
• IIH without papilledema: Rare subtype that meets all other criteria but lacks papilledema 1, 2
• Fulminant IIH: Characterized by precipitous decline in visual function within 4 weeks of diagnosis 1

Common Pitfalls and Caveats

• Headache presentation in IIH can mimic other primary headache disorders, making clinical diagnosis challenging 2
• Papilledema may be subtle or absent in some cases (IIH without papilledema) 1, 2
• When diagnostic uncertainty exists regarding papilledema, consultation with an experienced clinician is recommended before invasive tests 1
• Visual evoked potentials may detect alterations in the optic nerve before papilledema is clinically evident 6
• Recent research proposes that IIH can be defined by two out of three objective findings: papilledema, opening pressure ≥25 cm CSF, and ≥3 neuroimaging signs 5