A 35-year-old HIV-positive man comes to you with a 6-month history of progressive memory loss and incontinence. He is taking zidovudine and a protease inhibitor. Examination demonstrates deficits in cognitive and fine motor control functions. Lab shows a CD4 cell count of 25/mm3. MRI studies reveal moderate brain atrophy but no focal lesions. LP shows no CSF abnormalities. Most likely diagnosis

AIDS may lead to various complications affecting the CNS. Among these, HIV encephalitis, clinically known as AIDS dementia complex, is the most common. The pathologic substrate is a subacute inflammatory infiltration of the brain caused by the direct spread of HIV to the CNS. Presence of the HIV genome can be demonstrated by in situ hybridizations in microglia and histiocytes. The diagnosis of HIV encephalitis (or AIDS dementia complex) must be reached by the exclusion of other infective and neoplastic conditions associated with AIDS. AIDS dementia complex is characterized by cognitive impairment, incontinence, impairment of motor skills, and confusion. MRI studies and CSF analysis are useful in excluding other CNS diseases. CMV encephalitis usually affects the periventricular regions of the brain and the retina. CMV encephalitis is usually associated with disseminated infection. CMV can be isolated in the CS Ref - Harrison's principles of internal medicine 20e pg 1501,1349