Idiopathic Intracranial Hypertension Causes and Risk Factors

Intracranial hypertension is a condition due to high pressure within the spaces that surround the brain and spinal cord. These spaces are filled with cerebrospinal fluid (CSF), which cushions the brain from mechanical injury, provides nourishment, and carries away waste.

The most common symptoms of intracranial hypertension are headaches and visual loss, including blind spots, poor peripheral (side) vision, double vision, and short temporary episodes of blindness.

Many patients experience permanent vision loss. Other common symptoms include pulsatile tinnitus (ringing in the ears) and neck and shoulder pain.

Intracranial hypertension can be either acute or chronic. In chronic intracranial hypertension, the increased CSF pressure can cause swelling and damage to the optic nerve—a condition called papilledema.

Chronic intracranial hypertension can be caused by many conditions including certain drugs such as tetracycline, a blood clot in the brain, excessive intake of vitamin A, or brain tumor.

It can also occur without a detectable cause. This is idiopathic intracranial hypertension (IIH).

Because the symptoms of IIH can resemble those of a brain tumor, it is sometimes known by the older name pseudotumor cerebri, which means “false brain tumor.”

Signs and symptoms

Patients with IIH usually present with symptoms related to increased ICP and papilledema. Symptoms of increased ICP may include the following:

  • Headaches, typically nonspecific and varying in type, location, and frequency
  • Diplopia, usually horizontal but rarely vertical
  • Pulsatile tinnitus
  • Radicular pain, usually in the arms (uncommon symptom)
  • Rarely, patients presenting with increased ICP with related optic nerve edema may be asymptomatic.

Symptoms of papilledema may include the following:

  • Transient visual obscurations, often predominantly or uniformly orthostatic
  • Progressive loss of peripheral vision in one or both eyes
  • Blurring and distortion (ie, metamorphopsia) of central vision
  • Sudden visual loss
  • Nonspecific symptoms of IIH may include dizziness, nausea, vomiting, photopsias, and retrobulbar pain.[4]

The most significant physical finding is bilateral disc edema secondary to the increased ICP. In more pronounced cases, macular involvement with subsequent edema and diminished central vision may be present.

High-grade and atrophic papilledema in addition to subretinal hemorrhages are poor visual prognostic signs. Uncontrolled papilledema results in progressive peripheral visual field constriction or nerve fiber bundle defects.

Sudden loss of central vision may result from an associated anterior ischemic optic neuropathy, a vascular occlusion, or an associated subretinal neovascular membrane

Visual function tests are the most important parts of the neurologic examination for diagnosing and monitoring patients with IIH. Such tests include the following:

  • Ophthalmoscopy
  • Visual field assessment
  • Ocular motility examination

Who is at risk for IIH?

An estimated 100,000 Americans have IIH, and the number is rising as more people become obese or overweight. The disorder is most common in women between the ages of 20 and 50; about 5 percent of those affected are men.

Obesity, defined as a body mass index (BMI) greater than 30, is a major risk factor. BMI is a number based on your weight and height. The Centers for Disease Control and Prevention offers an online BMI calculator.

A recent gain of 5-15 percent of total body weight is also considered a risk factor for this disorder, even for people with a BMI less than 30.

How is IIH diagnosed?

A thorough medical history and physical exam are needed to identify risk factors for IIH and to evaluate for the many potential causes of increased intracranial pressure.

A neurological exam will also be performed. In IIH, the exam is normal except for findings related to increased intracranial pressure, including papilledema, visual loss, and possible weakness in the lateral rectus muscles, which are located near your temples and help turn the eyes outward.

Weakness in these muscles can cause the eyes to turn inward, toward the nose, producing double vision.

A number of vision tests may also be performed, including a comprehensive dilated eye exam to look for signs of papilledema. Visual field testing is done to evaluate your peripheral vision.

This testing measures the area of space you can see at a given instant without moving your head or eyes.

Brain imaging, including computed tomography (CT) and magnetic resonance imaging (MRI) scans, will be performed to look for a brain tumor, injury, or other potential cause for your symptoms. Normal findings on these exams are essential to a diagnosis of IIH.

A lumbar puncture, also known as a spinal tap, will be performed. In this procedure, a needle is inserted into a CSF-filled sac below the spinal cord in the lower back.

The CSF pressure will be measured, and a small amount of CSF will be collected for analysis to look for causes of increased intracranial pressure. The procedure may also cause a temporary reduction in CSF pressure and symptoms.

Treatment

  • Acetazolamide
  • Weight loss
  • Drugs used for migraine, especially topiramate

Treatment is aimed at reducing pressure, preserving vision, and relieving symptoms. The carbonic anhydrase inhibitor acetazolamide

(250 mg po qid) is used as a diuretic. Obese patients are encouraged to lose weight, which may help reduce intracranial pressure.

Serial lumbar punctures are controversial but are sometimes used, particularly if, while waiting for definitive treatment, vision is threatened. Any potential causes (disorders or drugs) are corrected or eliminated if possible.

Drugs used for migraine (particularly topiramate

, which also inhibits carbonic anhydrase) may relieve headache. NSAIDs can be used as needed.

If vision deteriorates despite treatment, optic nerve sheath fenestration, shunting (lumboperitoneal or ventriculoperitoneal), or endovascular venous stenting may be indicated.

Bariatric surgery with sustained weight loss may cure the disorder in obese patients who were otherwise unable to lose weight.

Frequent ophthalmologic assessment (including quantitative visual fields) is required to monitor response to treatment; testing visual acuity is not sensitive enough to warn of impending vision loss.

Key Points

  • Consider idiopathic intracranial hypertension if patients, particularly overweight women, have a daily generalized headache with or without visual symptoms; check visual fields and optic fundi.
  • Diagnose based on results of brain imaging (preferably MRI with venography) and, if not contraindicated, lumbar puncture.
  • Advise weight loss and treat with acetazolamide

Do frequent ophthalmologic assessments (including quantitative visual fields) to monitor response to treatment.

What is the prognosis?

For most people, IIH usually improves with treatment. For others, it progressively worsens with time, or it can resolve and then recur. About 5-10 percent of women with IIH experience disabling vision loss. Most patients do not need surgical treatment.

What research is being done?

For decades, acetazolamide has been the drug of choice for treating IIH, but with little evidence that it helped and no established usage guidelines.

The NEI-funded IIH Treatment Trial was designed to investigate the benefits of acetazolamide for IIH in patients with mild visual loss, and balance them against the drug’s known side effects.

The trial compared acetazolamide plus a weight loss plan, versus the same weight loss plan with a placebo pill, among 161 women and four men who had mild vision loss from IIH.

To limit side effects, the dosage was gradually increased to a maximally tolerated dose or up to 4 grams daily. In 2014, the researchers reported that the drug—weight loss combination helped to preserve and even restore vision over a six-month period. The trial will continue for a total of five years.

There is also ongoing research to determine what causes IIH. There have been some reports of IIH in multiple generations within families, suggesting that genes may play a role.

Because of its relationship to gender and obesity, there is a strong possibility that hormones contribute to IIH. Some hormones are actually released from fatty tissue, and are being studied as potential factors in the disease. The IIH

Treatment Trial includes procedures to address the role of genetics and hormones in IIH.

Information on other clinical trials on IIH can be found in http://www.clinicaltrials.gov, a Web-based resource that provides information on publicly and privately supported clinical studies on a wide range of diseases and conditions.

The website is maintained by the National Library of Medicine at the National Institutes of Health.

Source & More Info: E Medicine, Merck Manuals and nei.nih.gov

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