October 04, 2010

USMLE 2 Question 4

A twelve year old girl develops a change in mental status with psychosis over a 24 day period. On examination she is found to be febrile and appears restlessness. She has a CT scan which is normal. She is admitted but deteriorates over the next 24 hours and passes away in the intensive care unit.

An autopsy reveals severe edema, hemorrhages and necrosis confined primarily to the temporal lobes. Histology reveals intranuclear inclusion bodies.

A likely diagnosis is

a) herpes encephalitis
b) child abuse
c) meningitis
d) cerebral glioma
e) infectious mononucleosis

The correct answer is A

Clinically, herpes encephalitis is characterized by rapid onset of fever, chills, restlessness, and signs of increased intracranial pressure. The mortality rate of herpes encephalitis is at least 25%.

The characteristic gross appearance of herpes encephalitis include edema, hemorrhages and necrosis confined primarily to the temporal lobes. The degree of edema is evidenced by the medial displacement of the uncal gyri. The involvement may be bilateral or may be unilateral.

In the acute stages, microscopic examination reveals vascular destruction with infiltrates of neutrophils and lymphocytes as shown on this slide. In the later stages, glial proliferation becomes the prominent feature.

The histological feature which characterizes herpes simplex encephalitis is the finding of eosinophilic intranuclear inclusion bodies (Cawdry type A). The inclusions may be seen in neurons, astrocytes, and oligodendroglia. At the ultrastructural level, the nuclear inclusions of herpes simplex are found to contain viral particles with a characteristic bull's eye appearance.

Herpes simplex, a DNA virus, is carried by a majority of the human population. The virus is harbored in the trigeminal ganglia, and produces lesions in the oral mucosa when activated by stress. Herpes simplex encephalitis arises sporadically and does not necessarily occur in people with a history of oral lesions.

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