Diagnostic criteria include demonstrating elevated intracranial pressure by lumbar puncture, with an opening pressure greater than 200 mm H2O in the nonobese and greater than 250 mm H2O in the obese. Lumbar puncture needs to be performed in the lateral decubitus position with legs extended and with the patient relaxed. Falsely elevated pressures may occur in a sitting or prone position, or with anxiety. Cerebrospinal fluid (CSF) composition is normal. Neuroimaging studies tend to be unremarkable, although magnetic resonance imaging (MRI) may show findings of intracranial hypertension, including dilated optic nerve sheaths and an empty sella turcica. Diagnosis may require examination by an ophthalmologist because early or mild papilledema can be difficult to detect. Dilated funduscopic exam also helps differentiate true papilledema from pseudopapilledema secondary to optic disc drusen, tilted optic discs, or other mimickers. Photographs of the optic disc can serve as a baseline for serial monitoring. Formal visual perimetry should be performed. The most common finding is an enlarged blind spot; arcuate defects, inferonasal visual loss, or generalized visual field constriction may also be seen.
As IIH is by definition idiopathic, secondary causes of intracranial hypertension must be excluded: (1) mass lesions (i.e., intracranial tumor or abscess), (2) decreased CSF absorption via arachnoid granulations (e.g., adhesions after meningitis or subarachnoid hemorrhage), (3) increased CSF production (e.g., choroid plexus papilloma), and (4) venous outflow obstruction (e.g., cerebral venous sinus thrombosis). Because venous sinus thrombosis may mimic IIH, imaging of cerebral veins with magnetic resonance venography (MRV) is indicated with the standard MRI. Secondary intracranial hypertension also occurs with various metabolic, toxic, and hormonal disturbances, including imbalances in growth hormone, thyroid hormone, or aldosterone, and medications, including tetracycline, vitamin A, lithium, amiodarone, and corticosteroids (especially on withdrawal).
Permanent visual loss is the major morbidity associated with IIH, and management strategies depend on the degree and progression of papilledema. Serial photographs of the optic disc and serial testing of visual fields help guide treatment. The therapeutic goals are symptomatic relief by analgesia and reduction of CSF pressure. Weight reduction is very important in the management of overweight patients with IIH. If the patient has no visual loss and mild-to-moderate headache, weight loss and pain management may be all that is necessary. If the patient is taking medicines that exacerbate intracranial hypertension, these should be discontinued.
Acetazolamide is the most commonly used medical therapy for IIH. It is a carbonic anhydrase inhibitor and is thought to influence intracranial hypertension by inhibiting choroid plexus CSF secretion. It also may decrease appetite leading to weight loss.
Patients with visual loss require urgent treatment with corticosteroids to rapidly decrease intracranial pressure. However, because of their many potential side effects (weight gain, fluid retention, and rebound increased intracranial pressure on withdrawal of use), corticosteroids are not suitable for long-term care.
Medically intractable IIH can be treated with surgical procedures, such as optic nerve sheath fenestration or CSF shunting. Surgery is primarily indicated for visual loss or worsening vision due to papilledema.
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