Encephalitis
A severe inflammation of the brain, encephalitis is characterized by intense lymphocytic infiltration of brain tissues and the leptomeninges. This causes cerebral edema, degeneration of the brain’s ganglion cells, and diffuse nerve cell destruction.
Encephalitis is usually caused by a mosquito-borne or, in some areas, a tick-borne virus. However, transmission by other means may occur through ingestion of infected goat’s milk and accidental injection or inhalation of the virus. (See Types of encephalitis.)
Causes
Encephalitis usually results from infection with arboviruses specific to rural areas. In urban areas, encephalitis is usually caused by enteroviruses (coxsackievirus, poliovirus, and echovirus). Other causes include herpesvirus, mumps virus, adenoviruses, and demyelinating diseases after measles, varicella, rubella, or vaccination.
Complications
Potential complications associated with viral encephalitis include bronchial pneumonia, urine retention, urinary tract infection, pressure ulcers, and coma. Seizure disorder, parkinsonism, and mental deterioration may also occur.
Assessment
All forms of viral encephalitis have similar clinical features that vary according to the severity of the disease. The severity of arbovirus encephalitis may range from subclinical to rapidly fatal necrotizing disease. Herpes encephalitis also produces signs and symptoms that vary from subclinical to acute and usually fatal fulminating disease.
If encephalitis is the primary illness, the patient may be acutely ill when he seeks treatment because the nonspecific symptoms that occur before the onset of acute neurologic symptoms aren’t recognized as signs of encephalitis. Thus, the patient’s history may include reports of systemic symptoms, such as headache, muscle stiffness, malaise, sore throat, and upper respiratory tract symptoms that existed for several days before the onset of neurologic symptoms.
If neurologic symptoms have begun to occur, the patient’s history may reveal the sudden onset of altered levels of consciousness, from lethargy or drowsiness to stupor. The patient or a family member may also report seizures, which may be the only presenting sign of encephalitis.
On neurologic examination, the patient may be confused, disoriented, or hallucinating. He may also demonstrate tremors, cranial nerve palsies, exaggerated deep tendon reflexes, absent superficial reflexes, and paresis or paralysis of the extremities. In addition, the patient may complain of a stiff neck when his head is bent forward.
Vital signs usually reveal fever. The patient may also experience nausea and vomiting.
If the cerebral hemispheres are involved, the assessment findings may include aphasia, involuntary movements, ataxia, poor memory retention, and sensory defects, such as disturbances of taste and smell.
