What is idiopathic intracranial hypertension?

What is Idiopathic Intracranial Hypertension?

Idiopathic intracranial hypertension (IIH) is a disorder of elevated intracranial pressure without hydrocephalus, mass lesion, or identifiable underlying cause, characterized by normal cerebrospinal fluid composition and occurring predominantly in obese women of childbearing age. 1

Definition and Diagnostic Criteria

IIH represents raised intracranial pressure where no secondary etiology can be identified after thorough investigation. 1 The diagnosis requires:

• Elevated intracranial pressure documented by lumbar puncture with opening pressure ≥25 cm H₂O (≥250 mm H₂O) measured in the lateral decubitus position with the patient relaxed and legs extended 2
• Neuroimaging showing no evidence of hydrocephalus, mass, structural or vascular lesion, and no abnormal meningeal enhancement 2
• Normal cerebrospinal fluid composition 1
• Exclusion of cerebral sinus thrombosis via CT or MR venography 2

Epidemiology and Risk Factors

The annual incidence is increasing and was reported at 2.4 per 100,000 in the last decade (2002-2014). 1

The typical IIH patient is female, of childbearing age, with BMI >30 kg/m², and recent weight gain of 5-15% in the year preceding diagnosis. 2, 3 These three factors—female sex, obesity, and recent weight gain—define the classic patient profile. 3

Weight gain of 5-15% is the most important modifiable risk factor, and weight regain after initial loss is a major risk factor for disease recurrence throughout life. 3

Clinical Presentation

Headache is the most common presenting symptom, typically progressively more severe and frequent, though the phenotype is highly variable and may mimic other primary headache disorders. 1, 2 This variability makes clinical diagnosis challenging. 2

Additional symptoms include:

• Transient visual obscurations (unilateral or bilateral darkening of vision lasting seconds) 1, 2
• Pulsatile tinnitus (whooshing sound synchronous with pulse) 1, 2
• Visual blurring 1, 2
• Horizontal diplopia (typically from sixth nerve palsy) 1, 2
• Back pain, neck pain, dizziness, cognitive disturbances, and radicular pain 1, 2

None of these symptoms are pathognomonic for IIH, meaning they can occur in other conditions. 2

Physical Examination Findings

Papilledema is the hallmark finding in IIH and should be documented. 2 On cranial nerve examination, there should typically be no cranial nerve involvement other than possible sixth nerve palsy. 2 If other cranial nerves or pathological findings are involved, alternative diagnoses should be considered. 2

A rare subtype called "IIH without papilledema" meets all other criteria for IIH but lacks papilledema, making diagnosis more difficult. 2

Pathophysiology

Although the underlying pathogenesis is not fully understood, IIH has a striking association with obesity. 1 Outflow resistance of cerebrospinal fluid is increased in IIH, requiring intracranial pressure to increase for CSF to be absorbed. 4 Pregnancy or hormonal changes may contribute to disease onset or recurrence, and the reproductive age window in women suggests hormonal influence on disease pathophysiology. 3

Management Principles

Three main treatment principles guide IIH management: 1

1. Treat the underlying disease (primarily through weight loss as the disease-modifying treatment) 5
2. Protect the vision (surgical intervention when visual function declines) 5
3. Minimize headache morbidity 1

Prognosis and Complications

The main morbidity of IIH is visual loss, which is present in most patients and can usually be reversed if recognized early and treated. 4 Treatment failure rates for surgical interventions include worsening vision after initial stabilization in 34% of patients at 1 year and 45% at 3 years. 5 Failure to improve headache occurs in one-third to one-half of surgically treated patients. 5

Patients with IIH in ocular remission may still have ongoing headache morbidity requiring neurological management. 5