What are the characteristics of idiopathic intracranial hypertension?

Characteristics of Idiopathic Intracranial Hypertension

Idiopathic intracranial hypertension (IIH) is a syndrome of elevated intracranial pressure without identifiable cause, predominantly affecting obese women of childbearing age, characterized by papilledema, progressive headache, and visual symptoms, with CSF opening pressure ≥25 cm H₂O as the diagnostic threshold. 1

Patient Demographics

• The typical IIH patient is female, of childbearing age, with BMI >30 kg/m². 1, 2
• Over 80% of patients are overweight women. 3
• The incidence is increasing with rising obesity prevalence. 4
• Atypical patients who do not fit this demographic profile require more extensive investigation. 1

Clinical Symptoms

Primary Symptoms

• Headache is the most common presenting symptom, occurring in 92% of patients, typically progressively more severe and frequent. 1, 5
• The headache phenotype is highly variable and may mimic other primary headache disorders, making clinical diagnosis challenging. 1
• Transient visual obscurations (unilateral or bilateral darkening of vision lasting seconds) are common. 1
• Pulsatile tinnitus (whooshing sound synchronous with pulse) is characteristic. 1, 3
• Visual blurring occurs frequently. 1
• Horizontal diplopia may be present. 1, 2

Additional Symptoms

• Dizziness 1
• Neck pain and back pain 1
• Cognitive disturbances 1
• Radicular pain 1
• Tinnitus, hearing loss, and balance disturbance may occur 3
• None of these symptoms are pathognomonic for IIH. 1

Physical Examination Findings

Ophthalmologic Signs

• Papilledema is the hallmark finding in IIH and must be documented. 1, 2
• IIH without papilledema is a rare subtype (occurring in only 5-6% of patients) that meets all other criteria but lacks papilledema. 1, 6
• Visual field loss is common. 7

Neurologic Signs

• Unilateral or bilateral sixth cranial nerve palsy is the typical cranial nerve involvement. 1, 7, 4
• If other cranial nerves or pathological findings are involved, alternative diagnoses should be considered. 1
• Complete ophthalmoplegia is a rare presentation. 7

Diagnostic Criteria

CSF Pressure Requirements

• CSF opening pressure must be ≥25 cm H₂O (≥250 mm H₂O) measured in the lateral decubitus position. 1
• Proper measurement technique requires the patient in lateral decubitus position, relaxed, with legs extended. 1
• Pressure may fluctuate; repeat lumbar puncture at 2 weeks may be needed if initial pressure is borderline. 1

Neuroimaging Characteristics

• Neuroimaging must show no evidence of hydrocephalus, mass, structural or vascular lesion, and no abnormal meningeal enhancement. 1
• MRI brain is preferred and should be performed within 24 hours. 1, 2
• CT or MR venography is mandatory to exclude cerebral sinus thrombosis. 1, 2

Typical Neuroimaging Findings in IIH

• Empty or partially empty sella 2
• Increased optic nerve tortuosity 2
• Enlarged optic nerve sheath 2
• Flattened posterior globe/sclera 2
• Intraocular protrusion of optic nerve head 2
• Transverse sinus stenosis 2
• Optic nerve sheath with filled out cerebrospinal fluid spaces 4

Disease Patterns and Prognosis

Clinical Subtypes

• Fulminant IIH requires emergency referral and management. 2, 5
• Typical IIH is the most common form. 5
• Atypical IIH requires more in-depth investigation. 1, 5

Long-term Course

• Headaches may persist despite normalization of intracranial pressure, with 68% of patients continuing to have headaches 6 months after CSF diversion and 79% at 2 years. 5
• Many patients develop migrainous headaches superimposed on ICP-related headaches. 5
• IIH may recur throughout life, particularly with weight regain after initial loss. 5
• Pregnancy or hormonal changes may contribute to recurrence. 5
• Severe papilledema at presentation is a negative prognostic factor. 5

Visual Outcomes

• Visual impairment is a serious complication that may not be recognized by patients. 4
• Treatment failure with worsening vision after initial stabilization occurs in 34% at 1 year and 45% at 3 years. 2, 5
• VEP investigation may detect alterations in the optic nerve before papilledema is visible on ophthalmoscopic examination. 6

Common Pitfalls

• The highly variable headache presentation can mimic other primary headache disorders, delaying diagnosis. 1
• Patients must be informed early about the risks of medication overuse headache. 2
• Visual deterioration may not be recognized by patients themselves, requiring systematic monitoring. 4
• CSF otorrhea or rhinorrhea may be presenting features that lead patients to otolaryngology rather than neurology. 3
• IIH is associated with obstructive sleep apnea, which should be screened for. 3