What is Hypertensive Encephalopathy?

One of the complications of severe hypertension, or high blood pressure, is called hypertensive encephalopathy. This complication occurs when the brain does not receive enough blood supply to maintain life and function. It is important to differentiate hypertensive encephalopathy from other cerebrovascular diseases such as cerebral ischemia, stroke, delirium, seizure, and uremic encephalopathy, because the treatment is different. If left untreated, hypertensive encephalopathy can result in coma or death within a few hours. This is the reason why it is called a hypertensive emergency.

Hypertensive encephalopathy is very rare and affects only 1% of people who suffer from long-standing hypertension. The affected person is usually male and middle aged. When Oppenheimer and Fishberg first used the term “hypertensive encephalopathy” in 1928, they were referring to a constellation of symptoms that included severe hypertension, acute inflammation of the kidney or nephritis, and cerebral dysfunction. In the past, cerebral symptoms that accompanied this type of encephalopathy involved cerebral hemorrhage, transient ischemia, dizziness, and headache. These symptoms were all associated with malignant hypertension, a syndrome wherein either a known hypertensive person experiences a sudden increase of blood pressure or a previously non-hypertensive person experiences an abrupt and unpredictable increase in blood pressure.

The definition of hypertensive encephalopathy, however, has been modified. It now refers to the transient and reversible neurological dysfunction in a person who is experiencing the malignant phase of hypertension. Other causes of this condition include acute nephritis, abrupt non-intake of antihypertensive drugs, Cushing’s syndrome, pheochromocytoma, and renal artery thrombosis. Pregnant women who are suffering from preeclampsia or eclampsia as well as drug users who take cocaine, lysergic acid diethylamide (LSD), and amphetamines are also at risk for this condition.

A person with this condition would complain of a sudden onset of severe headache, dizziness, confusion, blurry or impaired vision, nausea, vomiting, and seizures. When the doctor examines the patient’s eyes, papilledema or swelling of the optic disk is observed, together with hemorrhages, cotton wool spots, and exudates. These findings on funduscopy are collectively called grade IV retinal changes, and signify an increase in intracranial pressure.

How this type of encephalopathy is addressed can be explained by its pathophysiology. Normally, the flow of blood through the brain is maintained despite changes in arterial pressure. For instance, even if the systolic blood pressure of an individual increases from 60 to 150 millimeters of mercury (mmHg), the blood supply would not be compromised because of a process called autoregulation. This is because the small blood vessels called arterioles constrict as a response to a decrease in blood pressure, while they dilate in response to an increase in blood pressure. When the autoregulatory mechanism fails at the upper range of blood pressure, the result is dilatation of blood vessels and excessive perfusion, or hyperperfusion, of the brain.

The goal of therapy is therefore to decrease blood pressure to restore normal perfusion. Treatment of hypertensive encephalopathy involves the administration of drugs through the parenteral route. These drugs include nicardipine, labetalol, and nitroprusside. They help by dilating the blood vessels, thereby lowering the blood pressure.