What is the most common cause of meningoencephalitis in AIDS patients?

The most common cause of meningoencephalitis in AIDS patients is Cryptococcus neoformans. This encapsulated yeast is particularly associated with individuals who have advanced HIV infection and a CD4 cell count less than 350 cells/mm³, where the risk of opportunistic infections significantly increases.

Cryptococcus neoformans can enter the body through inhalation of spores, leading to pneumonia, but it can also disseminate to the central nervous system, causing cryptococcal meningitis. Symptoms may include fever, headache, neck stiffness, and altered mental status. The diagnosis is commonly made through the detection of cryptococcal antigen in the serum or cerebrospinal fluid, and treatment typically involves antifungal medications such as amphotericin B and flucytosine.

While cytomegalovirus, Toxoplasma gondii, and Mycobacterium tuberculosis can also affect AIDS patients, they are less commonly associated specifically with meningoencephalitis compared to Cryptococcus neoformans. Toxoplasma gondii primarily causes focal brain lesions, and Mycobacterium tuberculosis can lead to tuberculous meningitis, but both are not as prevalent as cryptococcal infections in this population.