hypertensive encephalopathy

Background

Hypertension affects more than 60 million Americans. With adequate control, fewer than 1% of patients experience a hypertensive crisis. Hypertensive crisis is classified as hypertensive emergency or hypertensive urgency. Acute or ongoing vital target organ damage, such as damage to the brain, kidney, or heart, in the setting of severe hypertension is considered a hypertensive emergency. It requires a prompt reduction in blood pressure within minutes or hours. The absence of target organ damage in the presence of severe elevation of blood pressure with diastolic blood pressure frequently greater than 120 mm Hg is considered hypertensive urgency, and it requires reduction in blood pressure within 24-48 hours. A continuum exists between the clinical syndrome of hypertensive urgency and emergency; hence, their distinction may not always be clear and precise.

In 1928, Oppenheimer and Fishberg introduced the term hypertensive encephalopathy 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. 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 the neurologic impairment from an elevated intracranial pressure.

Hypertensive encephalopathy describes the transient migratory neurologic symptoms associated with the malignant hypertensive state in hypertensive emergency. The clinical symptoms usually are reversible with prompt initiation of therapy. In the evaluation of an encephalopathic patient, exclude systemic disorders and various cerebrovascular events that may present with a similar constellation of clinical findings.

Pathophysiology

The clinical manifestations of hypertensive encephalopathy are due to increased cerebral perfusion from the loss of blood-brain barrier integrity, resulting 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 and an intact blood-brain barrier.

In chronically hypertensive individuals, the cerebral autoregulatory range gradually is shifted to higher pressures as an adaptation to chronic elevation of systemic blood pressure. This cerebral autoregulatory 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. 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 clinically manifest as neurologic deficits and altered mentation in hypertensive encephalopathy.

Frequency

United States

Of the 60 million Americans with hypertension, fewer than 1% of patients develop a hypertensive emergency.

Mortality/Morbidity

The morbidity and mortality associated with hypertensive encephalopathy are related to the degree of target organ damage. Without treatment, the 6-month mortality rate for hypertensive emergencies is 50%, and the 1-year mortality rate approaches 90%.

Race

The frequency of hypertensive encephalopathy corresponds to the occurrence 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.

Sex

Hypertension is more prevalent in men than in women.

Age

Hypertensive encephalopathy mostly occurs in middle-aged individuals who have a long-standing history of hypertension.

Case Report

A 77-year-old man with a past medical history of hypertension,

a greater than 100 pack-year history of tobacco smoking, and right

internal carotid artery 90% stenosis was admitted to our institution

after new onset dysarthria and inappropriate behavior. His neurological

examination showed left hemineglect, confusion, and a

blood pressure of 250/150 mm Hg. In addition, there was prominent

dysarthria and dysphagia, with characteristic bulbar features

of hypophonia and oropharyngeal weakness. There was no seizure

activity, headache, or visual changes. Laboratory studies were unremarkable

(sodium 139 mM/l) except for a creatinine of 2.5 mg/dl

(baseline). He underwent MRI ( fi g. 1 c, d) which showed T2-weighted

hyperintensities in bilateral posterior cerebral white matter as

well as in the pontine and ventral medullary white matter, which

had not been observed on prior neuroimaging ( fi g. 1 a, b). DWI

showed no evidence of cytotoxic edema (data not shown). The patient

was transferred to the cardiac care unit, where with aggressive

blood pressure control, his confusion, hemiparesis and neglect

promptly improved over days. The dysarthria and dysphagia also

improved over the ensuing 2 weeks. Serial MRIs were performed

that showed interval resolution of prior white matter abnormalities

( fi g. 1 e, f); these fi ndings correlated with his clinical improvement.

On discharge, he no longer required a nasogastric tube for feeding,

his speech was no longer dysarthric, and he had returned to his

functional baseline.

Discussion

Hypertensive encephalopathy is a disease entity that has recently

been well characterized in the literature. A broader category

for this neurological syndrome has been coined: reversible posterior

leukoencephalopathy or PRES  . Besides acute severe hypertension,

several other conditions have been associated with PRES,

including renal disease, immunosuppressive and cytotoxic drugs,

collagen vascular disorders such as systemic lupus erythematosus,

ecclampsia, and hematological disorders, including thrombotic

thrombocytopenic purpura or hemolytic uremic syndrome. On MRI, the most

commonly observed characteristics include hyperintensities

on the T2 -weighted sequences in the parietal and occipital

and isointense or hyperintense signals on apparent

diffusion coeffi cient maps, suggesting a vasogenic edema pattern

While the exact underlying mechanism of PRES is unknown,

there are two prevailing theories regarding its pathogenesis and

predilection for areas of the brain supplied by the posterior circulation.

The most widely accepted theory proposes that the myogenic

component of autoregulation in the posterior circulation, with its

sparse sympathetic innervation, becomes overwhelmed by either

elevated blood pressure or endothelial toxins, leading to a capillary

leak phenomenon and vasodilatation, resulting in vasogenic

rather than cytotoxic edema [. In contrast, another theory hypothesizes

that at elevated blood pressures or from endothelial toxins,

the autoregulatory system overcompensates, resulting in decreased

blood fl ow, ultimately resulting in ischemia and therefore cytotoxic

edema 

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