Idiopathic Intracranial Hypertension (IIH)
Idiopathic intracranial hypertension is a condition characterised by raised intracranial pressure without an identifiable structural or secondary cause.
Updated UKMLA guide to idiopathic intracranial hypertension based on European Headache Federation guideline, which covers causes, risk factors, symptoms, complications, diagnosis, and management.
Causes and Risk Factors
The exact underlying cause or pathogenesis of IIH remains unknown (thus idiopathic).
Primary risk factors: [Ref1][Ref2]
- Obesity – most significant risk factor (90-95% of patients are obese)
- Recent weight gain (5-15% of body weight)
- Occurring in the period preceding symptom onset or diagnosis is a major trigger and risk factor
- Women of childbearing age
Clinical Features
Typically presents in an obese female of childbearing age [Ref1][Ref2]
| Category | Clinical features |
|---|---|
| Headache | Most common symptom
However, the headache phenotype is highly variable, frequently mimicking a migraine |
| Ophthalmic features |
In true IIH, there should be absolutely no other cranial nerve deficits other than a potential CN VI palsy |
| Auditory and olfactory features |
|
| Systemic features |
|
Complications
- Permanent visual loss – most severe complication of IIH from prolonged papilloedema
- Chronic persisting headache – primary factor contributing to reduced QoL
- Medication-overuse headache may also develop due to the patient frequently relying on analgesia
- Cognitive impairment – may persist even after ICP and headache improve
Investigation and Diagnosis
Work-Up
| Category | Description / test |
|---|---|
| Clinical / bedside assessment |
|
| Neuroimaging |
|
| Lumbar puncture | If neuroimaging is normal → lumbar puncture
|
Do not perform lumbar puncture before neuroimaging if raised is suspected, due to the risk of brain herniation if there is a space-occupying lesion.
If raised is due to a space-occupying lesion, removing CSF from the spinal canal during lumbar puncture can create a pressure gradient between the skull and spinal canal. This can pull brain tissue downwards and cause brain herniation, especially tonsillar herniation, which can compress the brainstem and become rapidly fatal.
Diagnostic Criteria
Friedman diagnostic criteria – ALL of the following must be met: [Ref1][Ref2]
- Papilloedema is present
- Normal neurological examination (except CN VI palsy)
- Normal neuroimaging (i.e. no structural causes, meningeal enhancement, cerebral venous sinus thrombosis)
- Typical neuroimaging findings include empty sella, flattening of the posterior globe, distension of perioptic subarachnoid space (optic nerve sheath), transverse venous sinus stenosis
- Normal CSF analysis
- ↑ Lumbar puncture opening pressure (≥25 cm H₂O in adults or ≥28 cm H₂O in obese children)
IIH without papilloedema is a rare variant where there is ↑ ICP but no optic disc swelling, additional diagnostic findings are necessary.
Although not included in the diagnostic criteria, it is important to exclude secondary causes of raised ICP: [Ref1][Ref2]
- Medications
- Antibiotics: tetracyclines, fluoroquinolones
- Retinoids / vitamin A derivatives
- Hormones and steroids: corticosteroid withdrawal, anabolic steroids, growth hormone, COCPs
- Lithium
- Venous drainage obstruction
- Cerebral venous sinus thrombosis
- Jugular vein thrombosis
- SVC syndrome
- ↑ Central venous pressure (e.g. heart failure)
- Systemic and medical disorders
- CKD, uraemia, OSA, COPD
- SLE
- Infections: HIV, Lyme disease, varicella, psittacosis, CNS infections, otitis media, mastoiditis
- Endocrine disorder
- Addison’s disease, adrenal insufficiency
- Thyroid and parathyroid disorders
- Cushing’s syndrome
- Haematological disorders
- Anaemia (including severe iron deficiency)
- Thrombophilia
- Polycythaemia vera
- Syndromic / genetic conditions
- Down syndrome
- Turner syndrome
- Craniosynostosis
Exclusion of secondary causes is especially important in those who do not fit the “obese woman of reproductive age” demographic. [Ref]
Management
| Category | Management |
|---|---|
| Weight loss and management | For ALL patients with BMI >30 kg/m2
Bariatric surgery is increasingly considered for sustained, long-term weight loss in IIH |
| Medical therapy | To be considered in those with active symptoms with no immediate threat to vision
However, ~50% of patients discontinue acetazolamide because of its significant side effects (like fatigue, tingling, altered taste, and depression) |
| Surgical intervention | Surgery is ONLY indicated for those with visual disturbances / papilloedema
Options include:
If vision is actively declining (fulminant IIH), a lumbar drain or serial lumbar punctures can be used as a short-term temporary measure, while awaiting definitive surgery. Surgical interventions are NOT recommended exclusively for treating headaches due to poor outcomes, high revision rates, and risk of complications |
References
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Raised Intracranial Pressure (ICP)