Idiopathic intracranial hypertension: Clinical sciences

Idiopathic intracranial hypertension, or IIH, also known as pseudotumor cerebri, refers to an increased intracranial pressure of unknown precise etiology. Elevated intracranial pressure can cause debilitating headaches, but it can also lead to swelling of the optic disc, known as papilledema, which, if left untreated, can result in severe vision loss. Now, based on the immediate risk of vision loss, idiopathic intracranial hypertension can be classified as typical or fulminant.

Now, if your patient presents with a chief concern suggestive of idiopathic intracranial hypertension, first, obtain a focused history and physical exam. History will usually reveal an obese biological female of reproductive age with concerns, including headaches that may worsen with Valsalva maneuvers. Over time, elevated intracranial pressure can affect optic and abducens nerves and result in symptoms, such as blurred and double vision, or even vision loss. Vision loss may last only a few seconds, so it’s often referred to as transient visual obscurations. Additionally, your patient will report that vision loss typically occurs when changing positions, for example, when bending over to pick up a neurology textbook!

Next, the patient might complain of pulsatile tinnitus, which is sound transmitted from turbulent blood flow in narrowed transverse and sigmoid venous sinuses. Finally, history might reveal medications associated with idiopathic intracranial hypertension, including tetracycline antibiotics and retinoids, such as vitamin A derivatives or all-trans retinoic acid.

Now, here’s a clinical pearl to keep in mind! Idiopathic intracranial hypertension is usually seen in young, obese biological females. If your patient is not in this demographic group and presents with symptoms of elevated intracranial pressure, you should consider an alternative diagnosis, such as venous sinus thrombosis.

On physical examination, these patients are normotensive with normal mental status, which is important because idiopathic intracranial hypertension can mimic some concerns of individuals with malignant hypertension. Next, fundoscopy will reveal papilledema, which is characterized by disc elevation and blurred disc margin, while visual field testing might reveal visual field loss. You may also find decreased visual acuity. Finally, increased intracranial pressure can stretch the abducens nerve and cause unilateral or bilateral abducens nerve palsy!

For example, in a case of unilateral abducens nerve palsy, when the patient tries to look straight ahead, the affected eye will drift medially toward the nose. And on lateral gaze towards the affected side, the patient will be unable to abduct the affected eye, while the unaffected eye will adduct normally. Finally, on lateral gaze towards the unaffected side, the patient will adduct the affected eye normally toward the nose.

With these findings... you should suspect idiopathic intracranial hypertension, so your next step is to order a brain MRI with venography. Next, perform a lumbar puncture to determine opening pressure and analyze the CSF. If the imaging reveals structural abnormalities, venous sinus thrombosis, or meningeal enhancement; the lumbar puncture opening pressure is normal; or the CSF analysis reveals abnormal findings, you should consider an alternative diagnosis.

But what if the brain MRI has no abnormalities? On the flip side, let’s say the imaging does not show gross structural abnormalities, a venous sinus thrombosis, or meningeal enhancement. In addition, lumbar puncture opening pressure is elevated to at least 25 centimeters of water and CSF analysis reveals a normal composition, indicating no infection or inflammation, diagnose idiopathic intracranial hypertension.

Now, here’s a clinical pearl to keep in mind! While not required for diagnosis, some radiographic findings are commonly seen in individuals with idiopathic intracranial hypertension, including an empty sella turcica, posterior globe flattening, dilation of optic nerve sheaths, stenosis of transverse venous sinuses, and slit-like ventricles.

Once you make the diagnosis, assess for an immediate threat of vision loss to differentiate between typical and fulminant types of idiopathic intracranial hypertension. An immediate threat of vision loss exists if there has been less than 4 weeks between the onset of symptoms and severe vision loss, or if there has been rapid vision loss over the span of only a few days.

If both features are absent, diagnose typical idiopathic intracranial hypertension. In this case, treatment includes weight reduction, bariatric surgery, headache management, and carbonic anhydrase inhibitors, which are thought to work by decreasing CSF production. The most commonly used carbonic anhydrase inhibitor is acetazolamide. However, if your patient cannot tolerate acetazolamide due to side effects, such as paresthesias, altered taste, fatigue, nausea, or vomiting, you could consider topiramate.