- Author: Irawan Susanto, MD, FACP; Chief Editor: Michael R Pinsky, MD, CM, Dr(HC), FCCP, MCCM more...
The term hypertensive encephalopathy was introduced in 1928 to describe the encephalopathic findings associated with the accelerated malignant phase of hypertension. The terms accelerated and malignant were used to describe the retinal findings associated with hypertension, as follows:
Accelerated hypertension is associated with group 3 Keith-Wagener-Barker retinopathy, which is characterized by retinal hemorrhages and exudates on funduscopic examination
Malignant hypertension is associated with group 4 Keith-Wagener-Barker retinopathy, which is characterized by the presence of papilledema, heralding neurologic impairment from an elevated intracranial pressure (ICP)
With adequate control of hypertension, less than 1% of patients experience a hypertensive crisis. A hypertensive crisis is classified as either a hypertensive emergency or a hypertensive urgency, as follows:
Acute or ongoing vital target organ damage (eg, damage to the brain, kidney, or heart) in the setting of severe hypertension is considered a hypertensive emergency; a prompt reduction in blood pressure is required within minutes or hours
The absence of target organ damage in the presence of a severe elevation in blood pressure (with diastolic blood pressure frequently exceeding 120 mm Hg) is considered a hypertensive urgency; a reduction in blood pressure is required within 24-48 hours
A continuum exists between the clinical syndromes of hypertensive urgency and emergency; hence, the distinction between the 2 syndromes may not always be clear and precise in practice.
Hypertensive encephalopathy refers to the transient migratory neurologic symptoms that are associated with the malignant hypertensive state in a hypertensive emergency. The clinical symptoms are usually reversible with prompt initiation of therapy. In the evaluation of an encephalopathic patient, it is vital to exclude systemic disorders and various cerebrovascular events that may present with a similar constellation of clinical findings.
The clinical manifestations of hypertensive encephalopathy are due to increased cerebral perfusion from the loss of blood-brain barrier integrity, which results in exudation of fluid into the brain. In normotensive individuals, an increase in systemic blood pressure over a certain range (ie, 60-125 mm Hg) induces cerebral arteriolar vasoconstriction, thereby preserving a constant cerebral blood flow (CBF) and an intact blood-brain barrier.
In chronically hypertensive individuals, the cerebral autoregulatory range is gradually shifted to higher pressures as an adaptation to the chronic elevation of systemic blood pressure. This adaptive response is overwhelmed during a hypertensive emergency, in which the acute rise in systemic blood pressure exceeds the individual’s cerebral autoregulatory range, resulting in hydrostatic leakage across the capillaries within the central nervous system (CNS). Brain MRI scans have shown a pattern of typically posterior (occipital greater than frontal) brain edema that is reversible. This usually is termed reversible posterior leukoencephalopathy or posterior reversible encephalopathy syndrome (PRES).
With persistent elevation of the systemic blood pressure, arteriolar damage and necrosis occur. The progression of vascular pathology leads to generalized vasodilatation, cerebral edema, and papilledema, which are clinically manifested as neurologic deficits and altered mentation in hypertensive encephalopathy.
The most common cause of hypertensive encephalopathy is abrupt blood pressure elevation in a chronically hypertensive patient. Other conditions that can predispose a patient to elevated blood pressure and cause the same clinical situation include the following:
Chronic renal parenchymal disease
Withdrawal from hypertensive agents (eg, clonidine)
Pheochromocytoma, renin-secreting tumors
Sympathomimetic agents (eg, cocaine, amphetamines, phencyclidine [PCP], and lysergic acid diethylamide [LSD])
Eclampsia and preeclampsia
Head trauma, cerebral infarction
Collagen vascular disease
Ingestion of tyramine-containing foods or tricyclic antidepressants in combination with monoamine oxidase inhibitors (MAOIs)
Epidemiology and Prognosis
Of the 60 million Americans with hypertension, less than 1% develop a hypertensive emergency. The morbidity and mortality associated with hypertensive encephalopathy are related to the degree of target-organ damage. Without treatment, the 6-month mortality for hypertensive emergencies is 50%, and the 1-year mortality approaches 90%.
Hypertensive encephalopathy mostly occurs in middle-aged individuals who have a long-standing history of hypertension. Hypertension in general is more prevalent in men than in women. The frequency of hypertensive encephalopathy in various ethnic groups corresponds to the frequency of hypertension in the general population. Hypertension is more prevalent in black people, exceeding the frequency in other ethnic minority groups. The incidence of hypertensive encephalopathy is lowest in white people.
Refer patients to a dietitian to reduce the risk of vascular and hypertensive disease. Encourage lifestyle modifications, including smoking cessation, increasing exercise, moderation of alcohol, and avoidance of tobacco.
Educate patients about medication adherence and compliance, and strongly emphasize the need for medical compliance. Explain the effects of uncontrolled hypertension, including the complications of persistent hypertension. Inform patients about signs of acute target-organ damage, including visual changes, persistent headaches, and neurological changes.
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