AIDS Dementia Complex Scientific Facts Overview

AIDS dementia complex (ADC), also known as HIV dementia, HIV encephalopathy and HIV-associated dementia, is a common neurologic disorder associated with HIV infection and AIDS. Dementia occurs when neurocognitive impairment is severe enough to interfere with an individual's daily activities.

The human immunodeficiency virus, also known as HIV infection, is a retrovirus that causes AIDS (autoimmunodeficiency syndrome). The retrovirus primarily attacks the body's immune system, making the body extremely vulnerable to opportunistic infections (infections that occur in immunocompromised individuals).

HIV is transmitted from person to person via bodily fluids. It can be spread by sexual contact with an infected person, by sharing needles/syringes with someone who is infected, or, less commonly (and rare in countries where blood is screened for HIV antibodies), through transfusions with infected blood. HIV has been found in saliva and tears in very low quantities and concentrations in some AIDS patients. However, contact with saliva, tears or sweat has never been shown to result in HIV transmission.

The opportunistic infections that are associated with HIV do not cause ADC. Instead, HIV causes ADC. AIDS dementia complex is a metabolic encephalopathy (degenerative brain disease), which is caused by HIV infection and fueled by immune activation of brain macrophages (large white blood cells that engulf foreign substances in the body) and microglia (brain cells that digest dead neurons). These cells are infected with HIV and secrete neurotoxins that ultimately destroy neurons (brain cells), which cannot be regenerated. Therefore, the damage caused by ADC is irreversible.

In most cases, ADC occurs after several years of HIV infection. It is associated with low CD4+ T-cell levels (less than 200 cells/microliter of blood) and high plasma viral loads. ADC is considered an AIDS-defining illness, which means it is often the first sign of the onset of AIDS.

The condition is identified when an increase of monocytes and macrophages enter the central nervous system (CNS). In addition, patients experience gliosis (rapid production of glial cells in the brain), pallor of myelin sheaths (loss of the fatty layer surrounding the axons of nerves in the brain), abnormal dendritic cells and abnormal neuronal apoptosis (programmed cell death).

The condition causes cognitive impairment, motor dysfunction, speech problems and behavioral changes. While the progression of dysfunction is variable, ADC can be fatal if left untreated.

Highly active antiretroviral therapy (HAART) has led to a decline of ADC in developed countries. The frequency of ADC has declined from 30-60% of people infected with HIV to less than 20%. The therapy may not only prevent or delay the onset of ADC, but it may also improve mental function in patients who already have ADC.

Despite the widespread use of HAART, some people with HIV still develop ADC. Others cannot tolerate HAART. For these people, prognosis is usually poor. The dementia worsens over several months until the patient is no longer able to care for himself or herself. He or she becomes bedridden, unable to communicate and dependent on others for care.

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