Hypertensive encephalopathy (HE) is general brain dysfunction due to significantly high blood pressure. Symptoms may include headache, vomiting, trouble with balance, and confusion. Onset is generally sudden. Complications can include seizures, posterior reversible encephalopathy syndrome, and bleeding in the back of the eye.
In hypertensive encephalopathy, generally the blood pressure is greater than 200/130 mmHg. Occasionally it can occur at a BP as low as 160/100 mmHg. This can occur in kidney failure, those who rapidly stop blood pressure medication, pheochromocytoma, and people on a monoamine oxidase inhibitor (MAOI) who eat foods with tyramine. When it occurs in pregnancy it is known as eclampsia. The diagnosis requires ruling out other possible causes.
The condition is generally treated with medications to relatively rapidly lower the blood pressure. This may be done with labetalol or sodium nitroprusside given by injection into a vein. In those who are pregnant, magnesium sulfate may be used. Other treatments may include anti-seizure medications.
Hypertensive encephalopathy is uncommon. It is believed to occur more often in those without easy access to health care. The term was first used by Oppenheimer and Fishberg in 1928. It is classified as a type of hypertensive emergency.
Signs and symptoms
Hypertensive encephalopathy is most commonly encountered in young and middle-aged people who have hypertension. Overall, the condition is rare even among people with hypertension. Studies report that from 0.5 to 15% of people with malignant hypertension develop hypertensive encephalopathy. With the development of methods for detection and treatment of hypertension, hypertensive encephalopathy has been becoming more rare.
Symptoms of hypertensive encephalopathy typically start to occur 12–48 hours after a sudden and sustained increase in blood pressure. The first manifestation of these symptoms is a severe headache. Headache occurs in greater than 75% of patients. The patient becomes restless. Alterations in consciousness may follow several hours later, which include impaired judgement and memory, confusion, somnolence and stupor. If the condition is not treated, these neurological symptoms may worsen and ultimately turn into a coma. Other symptoms may include increased irritability, vomiting, diplopia, seizures, twitching and myoclonus of the limbs. Alterations in vision (vision blurring, hemivisual field defects, color blindness, cortical blindness) are common. They occur in 4 out of 11 cases (Jellinek et al. 1964). Hemiparesis, intracerebral hemorrhage, aphasia may also occur, but they are less common.
Pathogenesis
Hypertensive encephalopathy is caused by an increase in blood pressure. Several conditions may evoke blood pressure elevation: acute nephritis, eclampsia, crises in chronic essential hypertension, sudden withdrawal of antihypertensive treatment. Additionally, hypertensive encephalopathy may occur in pheochromocytoma, Cushing's syndrome, renal artery thrombosis.
The impairment of cerebral blood flow that underlies hypertensive encephalopathy is still controversial. Normally, cerebral blood flow is maintained by an autoregulation mechanism that dilates arterioles in response to blood pressure decreases and constricts arterioles in response to blood pressure increases. This autoregulation falters when hypertension becomes excessive. According to the over-regulation conception, brain vessels spasm in response to acute hypertension, which results in cerebral ischemia and cytotoxic edema. According to the autoregulation breakthrough conception, cerebral arterioles are forced to dilate, leading to vasogenic edema.
Cerebral edema can be generalized or focal. Brain ventricles are compressed, cortical gyri flattened.
Diagnosis
Diagnostic methods for hypertensive encephalopathy include physical examination, blood pressure measurement, blood sampling, ECG, EEG, chest X-ray, urinalysis, arterial blood gas analysis, and imaging of the head (CAT scan and/or MRI). Since decreasing blood pressure is essential, anti-hypertensive medication is administered without awaiting the results of the laboratory tests. Electroencephalographic examination detects the absence of alpha waves, signifying impaired consciousness. In people with visual disturbances, slow waves are detected in the occipital areas.