Human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS) patients may host a myriad of infectious, inflammatory, toxic, and neoplastic diseases that are not seen commonly in the immune-competent patient. Thus, it is important for the clinician to keep in mind the expanded differential diagnosis of mental status changes in the HIV patient. The etiology for mental status changes in general includes a vast differential of diseases in the categories of vascular, infectious, neoplastic, drugs, inflammatory, autoimmune, trauma, and endocrine or metabolic causes. In HIV/AIDS patients the differential must be expanded to include diseases and conditions related to immune dysfunction. The clinician should have a much lower threshold for suspecting a neurologic cause for mental status changes in the HIV/AIDS patient as compared with the immune-competent patient.

The initial workup for HIV/AIDS patients with new-onset mental status changes must include a contrasted head computed tomography (CT) scan to rule out intracranial mass lesions. A magnetic resonance imaging (MRI) with gadolinium is more sensitive for small intracranial lesions; however, the limited availability in some centers and the increased time to obtain images make CT scan a more practical initial imaging modality (Table 200.1).

In the HIV/AIDS patient it is important to obtain the head CT before performing a lumbar puncture (Fig. 200.1). A focal mass lesion may produce locally elevated intracranial pressure. Alumbar puncture done in this setting can result in a high pressure gradient between the lesion and lumbar cistern that forces the brain downward, resulting in fatal herniation. The most common mass lesions to consider are toxoplasmosis and primary central nervous system (CNS) lymphoma. The incidence of cerebral toxoplasmosis in HIV/AIDS patients ranges from 3% to 10% in the United States, while primary CNS lymphoma occurs in about 2% of patients.