Idiopathic Intracranial Hypertension

Idiopathic Intracranial Hypertension

formerly known as Benign Intracranial Hypertension (but not always benign!)

or pseudotumor cerebri

Essentially the presence of raised intracranial pressure in the absence of a structural cause (no mass lesion, no discernible obstruction to CSF [hydrocephalus] or venous outflow)

- should also have normal CSF composition

First described by Quincke in 1893 as "meningitis serosa"; first codified by Dandy in 1937

Epidemiology:

Most commonly occurs in obese women of childbearing age

- can also occur in children, males, and the elderly (but less common and suspect "secondary" causes)

Pathophysiology:

May be heterogenous group of pathologies but main theories include:

1. Increased resistance to CSF absorption

2. Increased CSF production

3. Increased venous sinus pressure (also leading to #1)

- certainly dural sinus occlusions may present identically to IIH with headaches and papilledema without focal findings

- elevations in measured venous sinus pressure seen may be due to raised ICP and not the cause of it, as shown by reductions in venous pressure with CSF drainage and lowering ICP

History:

Headache

- present in almost all cases (but can diagnose even if asymptomatic)

- diffuse, may wake at night and worse in morning

- increased with head movement, coughing or straining

- associated with nausea & vomiting +/- photophobia

Transient visual obscurations

Diplopia

- due to abducens nerve palsy

Pulsatile Tinnitus

May complain of neck stiffness although meningismus not seen

- should NOT see focal symptoms, seizures, or alterations in LOC (more suspicious for mass lesion or venous sinus thrombosis)

- if onset is acute and course is progressive, suspect secondary cause

Medications associated with IIH should be ascertained:

- Vitamin A & Retinoids (incl. isotretinoin, Accutane)

- Minocycline and tetracycline (used for acne; typically within weeks of starting)

- Human growth hormone (rhGH) incidence of up to 6.5 per 1000 children

- other drugs include lithium, amiodarone, corticosteroid withdrawal

Examination:

Papilledema

- blurring of disc margins (esp superior / inferior / nasal when mild)

- progresses to peripapillary hemorrhages and gross swelling of disc

- may not resolve immediately as ICP falls with treatment

- rarely absent despite documented high CSF opening pressure so not mandatory for dx (presence of optic atrophy or other disc pathology may preclude development of disc swelling)

Visual acuity: ensure that this is normal

- early loss of visual acuity is very unusual in IIH and then suspect optic nerve pathology such as optic neuritis or anterior ischemic optic neuropathy

Visual fields:

- blind spots may be enlarged with some peripheral constriction

CN VI Palsy:

- may see false-localizing (due to raised ICP) unilateral or bilateral

- other cranial nerves, power, sensation, and coordination should be normal

- level of consciousness should be normal

Rarely children with IIH can present with signs mimicking a posterior fossa lesion:

- including ataxia, facial palsy, nuchal rigidity, torticollis or Babinski sign

Investigations:

1. Neuroimaging:

- to rule out structural lesion (space-occupying mass) causing raised ICP

- this can be accomplished with a normal CT scan of the head (typically see 'slit-like' ventricles but not always)

- "empty sella" and flattening of posterior globe commonly found on imaging as well

- MRI with MRV may be optimal to rule-out occult venous sinus thrombosis as cause

2. CSF Pressure & Analysis:

- lumbar puncture with measurement of opening pressure is diagnostic if elevated > 25 cm

- documented in lateral decubitus position with legs extended and as relaxed as possible

- repeat if initial reading is normal with high diagnostic suspicion as fluctuations can occur

- composition including cell count and protein should be normal

Differential Diagnosis: of Raised ICP without Mass Lesion (ie pseudotumor syndrome)

1. Medical disorders

- Addison's disease

- Hypoparathyroidism

- COPD / Right heart failure with pulmonary hypertension

- Sleep apnea

- Renal failure

- Severe iron deficiency anemia

- Scurvy

2. Medications (see above)

3. Obstruction to venous drainage

- cerebral venous sinus thrombosis

- jugular vein thrombosis

Complications:

Intracranial hypertension is not always benign and can lead to vision-threatening complications

Visual loss is the major complication and may be irreversible

- assess visual acuity and visual fields closely to monitor for vision loss

- degree of papilledema is rough correlate of risk of visual loss but not always

- earliest signs of change include enlargement of the blind spots

- also arcuate scotomas, nasal steps and global constriction

Treatment:

1. Weight loss: for obese patients, this is the only proven therapy

- even mild reductions in weight can lead to improvements in signs & symptoms

2. Discontinue any potentially offending medications

- symptoms and papilledema usually resolve within weeks of stopping

3. Reduction in CSF production:

- acetazolamide (Diamox) starting 250 mg BID up to 1.5 - 3 g daily (unless sulfa allergy)

[warn patients about change in taste or tingling of lips or extremities when taking this]

- furosemide / lasix can be used as a second-line or adjunctive agent (or if sulfa allergy)

- corticosteroids appear to work in some cases, but can also cause weight gain !

4. Refractory cases: progressive symptoms or visual loss despite therapy

- optic nerve sheath fenestration is safe and effective to prevent visual loss with stabilization in visual acuity seen in most treated patients

(may be a site for CSF to leak out of subarachnoid space, reducing ICP overall, and can lead to protection of vision even in unoperated eye through this mechanism)

- lumboperitoneal shunting is useful to reduce ICP if headaches are resistant to therapy (but can have complications incl. low pressure syndrome with headache, infections, shunt failure)

- repeated lumbar punctures can be performed to lower ICP

- bariatric surgery to aid in weight loss can be considered if morbidly obese

References:

Friedman DI, Jacobson DM. Diagnostic criteria for idiopathic intracranial hypertension. Neurology 2002; 59: 1492-5.

Shin RK, Balcer LJ. Idiopathic intracranial hypertension Curr Treatment Options Neurol 2002; 4: 297-305.

Reviewed by: pending

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