What is idiopathic intracranial hypertension?
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.”
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.
How is IIH treated?
If a diagnosis of IIH is confirmed, regular visual field tests and comprehensive dilated eye exams are recommended to monitor any changes in vision.
Sustainable weight loss through healthy eating, salt restriction, and exercise is a critical part of treatment for people with IIH who are overweight. Studies show that modest weight loss, around 5-10 percent of total body weight, may be sufficient to reduce signs and symptoms. If lifestyle changes are not successful in reducing weight and relieving IIH, weight loss surgery may be recommended for those with a BMI greater than 40.
For many people, weight loss can be difficult to achieve and maintain. And for those who are able to adjust their weight, relief from IIH tends to be gradual. Acetazolamide (Diamox), a drug that decreases CSF production, is therefore often used as an add-on therapy to weight loss. The drug is taken orally. Common side effects include fatigue, nausea, tingling hands and feet, and a metallic taste, usually triggered by carbonated drinks. These can be reversed by lowering the dose or stopping the drug.
It’s important to remember that some medications, such as tetracycline, may help trigger IIH, and that stopping them may lead to improvement.
In rapidly progressive cases that do not respond to other treatments, surgery may be needed to relieve pressure on the optic nerve. Therapeutic shunting, which involves surgically inserting a tube to drain CSF from ventricles or inner brain cavities, can be used to remove excess CSF and lower pressure. In a procedure called optic nerve sheath fenestration, pressure on the optic nerve is relieved by making a small window into the covering that surrounds the nerve just behind the eyeball.
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.
The National Eye Institute (NEI) is part of the National Institutes of Health (NIH) and is the Federal government’s lead agency for vision research that leads to sight-saving treatments and plays a key role in reducing visual impairment and blindness.