Encephalopathy, Hypertensive

Chronic Htn, renal disease (particularly end-stage renal disease), malignancy, sympathomimetic drugs, and a history of transplantation and immunosuppressive therapies

Increased risk of myocardial ischemia, ventricular dysrhythmias, HF, aortic dissection, cerebral hemorrhage, coma, long-term neurologic disability, renal failure, or sudden death

Myocardial ischemia or infarction

Aortic dissection

HF

Pulm edema

Cerebral infarction (ischemic or hemorrhagic) or intracranial hemorrhage

Acute renal failure

Eclampsia in at-risk parturients

Microangiopathic hemolytic anemia

The most common clinical presentations of hypertensive emergencies are cerebral infarction (24.5%), pulm edema (22.5%), hypertensive encephalopathy (16.3%), and HF (12%).

Hypertensive encephalopathy is by definition a hypertensive emergency and has recently come to fall under the umbrella term PRES.

Hypertensive encephalopathy is a relatively rapidly evolving syndrome of severe Htn in association with (most commonly) seizures, headache, visual disturbances, altered mental status, vomiting, ataxia, and focal neurologic deficits that may become rapidly fatal.

Occurs when the systemic BP is elevated beyond the cerebral autoregulatory threshold of MAP, typically greater than 160 mm Hg (“autoregulation breakthrough”).

Differential Dx: Ischemic or hemorrhagic stroke (particularly posterior circulation stroke), toxicology syndrome from drugs of abuse (e.g., cocaine), encephalitis, and venous sinus thrombosis.

It is critically important to distinguish between ischemic stroke and hypertensive encephalopathy because the treatment for hypertensive encephalopathy is lowering of BP, whereas outcomes are improved with higher BPs after acute ischemic stroke and therefore antihypertensives are generally not recommended.

Hypertensive encephalopathy can develop in pts with or without chronic Htn. However, because the cerebral autoregulation curve is shifted to the right in chronically hypertensive pts, it may take significantly higher BPs for these pts to develop signs of encephalopathy.

As the name implies, PRES is usually reversible if diagnosed early and treated appropriately but can quickly become irreversible and fatal.

Diagnostic test of choice is MRI, which will reveal symmetric reversible T2 high signal intensities located in the occipital and parietal lobes as a result of subcortical vasogenic edema. CT is not sensitive for the lesions of PRES and will often be normal.

The critical event is failure of cerebral autoregulation (for any reason) leading to cerebrovascular endothelial dysfunction and vasogenic edema that renders the pt encephalopathic.

Leading theory of pathophysiology is that in the presence of increased cerebral perfusion pressure, the increased capillary hydrostatic pressure leads to vasogenic edema and may even disrupt the blood-brain barrier.

Chemokines and cytotoxic agents may play a role in the endothelial dysfunction, as evidenced by the existence of PRES in normotensive and even hypotensive pts (e.g., undergoing chemotherapy or septic shock).

Nonhypertensive causes and associations of PRES include:

• Endocrine disorders: Pheochromocytoma, renin-secreting tumor, Cushing disease, and Conn syndrome.

• Drug induced: Immunosuppressive therapy, chemotherapy, erythropoietin, MAOIs, abrupt discontinuation of antihypertensive drugs, sympathomimetic drugs, and drugs of abuse (e.g., cocaine, amphetamines, LSD).

• AIDS.

• Thrombotic thrombocytopenic purpura.

• Status post CEA (CEA hyperperfusion syndrome).

• Preeclampsia and eclampsia.

• Acute intermittent porphyria.

• Autonomic hyperreactivity, as with spinal cord lesions.