AIDS-defining conditions

CD4+ cell count < 500/mm³

• Kaposi sarcoma (typically occurs at CD4 count < 500)
• Lymphoma
• Mycobacterium tuberculosis

CD4+ cell count < 200/mm³

• Pneumocystis pneumonia
• Disseminated or extrapulmonary histoplasmosis
• Progressive multifocal leukoencephalopathy

CD4+ cell count < 100/mm³

• Cerebral toxoplasmosis
• Extrapulmonary cryptococcosis (especially cryptococcal meningitis)
• Cryptosporidiosis
  • Etiology: Cryptosporidium species
  • Clinical features: chronic, watery diarrhea (lasting > 1 month) with nausea and abdominal pains; typically at CD4 counts < 100
  • Diagnostics: acid-fast oocysts in stool
• Esophageal candidiasis or pulmonary candidiasis
  • Oropharyngeal candida, which is not AIDS-defining, is more common as CD4 counts decline, and may be seen when CD4 count is < 200–250.
  • Neutrophils are the most important immune cell in the defense against invasive Candida infection; therefore, patients with neutropenia (eg, following cytotoxic chemotherapy) are at high risk for invasive disease (eg, candidemia, meningitis). In contrast, T lymphocytes are more important for prevention of superficial, mucocutaneous infection (eg, thrush).
• Primary CNS lymphoma
• Disseminated and/or extrapulmonary Mycobacterium avium complex
• Cytomegalovirus infection

CD4+ cell count < 50/mm³

• Disseminated and/or extrapulmonary Mycobacterium avium complex
• Cytomegalovirus infection
• Aspergillosis
• Primary CNS Lymphoma (PCNSL)

Neurological complications

HIV-associated neurocognitive disorder (HAND)

• Definition: neurocognitive impairment in patients with HIV that cannot be attributed to a cause other than HIV infection. HAND is typically a diagnosis of exclusion.
• Etiology: thought to result from a combination of dissemination of HIV into the CNS and the resultant immune activation.
• Epidemiology: common even in patients with well-controlled HIV (affecting up to 50% of individuals)
• Clinical features
  • Early: mild impairment in attention, recall, and executive function
  • Advanced: HIV-associated dementia (considered an AIDS-defining condition)
    • Subcortical dementia: memory loss, depression, movement disorders, behavioral changes (e.g., apathy)
    • Severe neurologic deficits: altered mental state, aphasia, gait disturbances
    • More common in patients with advanced or untreated HIV
• Diagnostics
  • Imaging: CT or MRI brain without and with IV contrast
    • Diffuse cerebral atrophy; disproportionate to the patient's age
    • Patchy symmetrical changes in the periventricular and deep white matter
    • No mass effect, no contrast-enhancement
  • Histopathology shows giant cells with multiple nuclei (formed through fusion of HIV-infected monocytes).