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 support life and function. It is important to differentiate hypertensive encephalopathy from other cerebrovascular diseases such as cerebral ischemia, stroke, delirium, seizures, and uremic encephalopathy, because treatment is different. If left untreated, hypertensive encephalopathy can lead to coma or death within a few hours. This is why it is called a hypertensive emergency.
Hypertensive encephalopathy is very rare, affecting only 1% of people with 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 referred to a constellation of symptoms that included severe hypertension, acute kidney inflammation or nephritis, and brain dysfunction. In the past, cerebral symptoms that accompanied this type of encephalopathy included cerebral hemorrhage, transient ischemia, dizziness, and headache. All of these symptoms were associated with malignant hypertension, a syndrome in which a known hypertensive person experiences a sudden increase in blood pressure or a previously non-hypertensive person experiences an abrupt and unpredictable increase in blood pressure.
However, the definition of hypertensive encephalopathy 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 withdrawal of antihypertensive drugs, Cushing's syndrome, pheochromocytoma, and renal artery thrombosis. Pregnant women suffering from pre-eclampsia 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, blurred or impaired vision, nausea, vomiting, and seizures. When the doctor examines the patient's eyes, papilledema or swelling of the optic disc is noted, along with hemorrhages, cotton wool spots, and exudates. These funduscopy findings are collectively called grade IV retinal changes and signify increased intracranial pressure.
The way this type of encephalopathy is approached can be explained by its pathophysiology. Normally, blood flow through the brain is maintained despite changes in blood pressure. For example, even if an individual's systolic blood pressure rises from 60 to 150 millimeters of mercury (mmHg), the blood supply would not be compromised due to a process called autoregulation. This is because small blood vessels called arterioles constrict in response to a drop in blood pressure, while they dilate in response to an increase in blood pressure. When the autoregulatory mechanism fails in the upper range of blood pressure, the result is dilation of the blood vessels and overperfusion or hyperperfusion of the brain.
The goal of therapy is therefore to lower blood pressure to restore normal perfusion. Treatment of hypertensive encephalopathy involves the administration of drugs parenterally. These medications include nicardipine, labetalol, and nitroprusside. They help by dilating blood vessels, thereby lowering blood pressure.