MEDizzy - Histologic examination of the brain from a 39-year-old man

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Nervous System

Histologic examination of the brain from a 39-year-old man who died from encephalitis finds numerous microglial nodules composed of mononuclear cells, microglia, and scattered multinucleated giant cells. Which one of the following is most likely to be present within the cells of these microglial nodules?

ExplanationMicroglial nodules within the brain that are composed of mononuclear cells, microglia, and scattered multinucleated giant cells are characteristic of meningoencephalitis caused by HIV (human immunodeficiency virus). Previously most patients with AIDS at some time during their illness developed neurologic symptoms, but the incidence of this has markedly decreased following the use of antiretroviral therapy. In contrast, herpes simplex virus produces characteristic Cowdry type A intranuclear inclusions in neurons and glial cells, while rabies forms characteristic inclusions within neurons called Negri bodies. Rabies, caused by a single-stranded RNA rhabdovirus, is transmitted by the bite of a rabid animal, usually a dog, and travels to the brain via peripheral nerves. Symptoms caused by the destruction of neurons in the brainstem include irritability, difficulty in swallowing, and spasms of the throat (these two resulting in “hydrophobia”), seizures, and delirium. The illness is almost uniformly fatal. Enlarged cells (cytomegaly) with intranuclear and intracytoplasmic inclusions are seen with cytomegalovirus infection. Finally, poliovirus does not infect the brain but rather it invades the anterior horn motor neurons of the spinal cord, where it causes muscular paralysis.