It has now been established that HIV can have a direct effect on the brain. AIDS dementia complex (ADC) is a term used to describe dementia, which is caused by the Human Immunodeficiency Virus (HIV). Other terms are sometimes used such as HIV/AIDS Encephalopathy, HIV/AIDS Related Brain Impairment and AIDS related dementia. The term ADC will be used in this text to refer to dementia in people with AIDS caused by HIV, which these terms also describe.

HIV is not the only cause of dementia in people suffering from AIDS. As a result of the body's weakened defence system, other kinds of viruses, bacteria or organisms can attack the brain. This kind of dementia is generally referred to as an "opportunist infection of the brain" as it literally takes opportunity of the weakened body. It is important to realise that it is a side effect of the presence of HIV in the body, whereas ADC is caused directly by HIV entering into the Central Nervous System, which is comprised of the brain and the spinal cord. This differentiation is all the more important as opportunist infections are often treatable.

Opportunist infections include :

• Cryptococcal Meningitis : An inflammation of the membrane covering the brain caused by a yeast-type fungus
• Cerebral Toxoplasmosis : This is caused by a parasite which can be passed on to people directly via the cat and indirectly by eating raw meat. It is the second most common opportunist infection and it is estimated that about one quarter of people with HIV are affected.
• Cytomegalovirus Retinitis : This infection is caused by a virus which is common in the general public. If left untreated it can lead to blindness and gastro-intestinal problems.
• Progressive Multifocal Leucoencephalopathy : The symptoms of this infection, which is caused by the JC virus, are quite similar to ADC.

The difference between dementia and cognitive impairment

The diagnosis of ADC is based on formal criteria. Therefore, even if a person seems to be showing clear signs of mental impairment, he or she may not be technically considered to be suffering from dementia. In such cases, a person may be described as suffering from moderate dementia, moderate or "cognitive" impairment - a term, which tends to be used to describe the worsening ability to think fast or clearly.

How common is ADC?

It is currently estimated that 8 to 16% of people with AIDS develop dementia. Those who do, tend to develop it in the later stages of the disease. The third quarterly report of 1996 of the European Centre for the Epidemiological Monitoring of AIDS provides the following figures concerning reported cases of HIV encephalopathy in adult/adolescents (over 13 years of age) and children (under 13 years of age) diagnosed since January 1994 in the WHO European region.

Factors which may mislead a person into believing that he/she has ADC

Often, people with HIV fear that they have dementia, when in fact their problems with concentration, memory and thinking are caused by other factors. These include :

• Being anxious, stressed or lonely
• Sleep disturbances
• Worry and fatigue caused by the extra problems that arise as a result of the illness (e.g. with daily life, with relationships, with employment etc.)
• Severe side effects of medication
• Toxins in the blood (e.g. caused by liver failure or extreme diarrhoea)
• Lack of oxygen to the brain (e.g. during an attack of pneumonia)
• The production of chemicals by the body in response to infections

Finally, some people may have a real psychotic breakdown due to emotional factors and extreme stress rather than the physical effects of HIV. Also, just as some members of the general public suffer from psychiatric problems, so too might some people with AIDS (and would have done even if they had not developed AIDS).

Is it possible to detect HIV in the brain?

Examining the brain with scans

Using the Computerised Axial Tomography (CAT) it is possible to obtain a kind of detailed X-ray. This method is not sensitive enough to be able to detect changes in the brain which reflect ADC but can be used to identify certain opportunist infections. Magnetic Resonance Imaging (MRI) can sometimes show up changes in the white matter in the brains of people with AIDS who have dementia. However, although there is no scan, which can definitely diagnose ADC, scanning can contribute to a more certain diagnosis.

Neuropsychological testing

Regular neuropsychological testing is effective in drawing attention to slight changes, which might alert doctors to the presence of dementia, whether it be caused by HIV or opportunist infections. It involves testing memory, concentration, quick thinking and quick moving.

Tests of the cerebrospinal fluid

This test involves analysing the "cerebro-spinal fluid" - a clear watery liquid, which is contained in a kind of hollow tube inside the spinal cord, which leads to the brain. Abnormalities in this liquid may include an excess of white blood cells, protein and immunoglobulin G (IgG) and the presence of HIV and the HIV protein p24. However, although safe for the patient, this test is usually avoided unless there is a strong suspicion of infection as it is rather unpleasant for the patient.

How does ADC develop?

HIV is capable of "unlocking" and entering T4 cells in the body, which are the cells that are responsible the body's defence system against diseases and infections. As stated earlier, HIV enters the Central Nervous System, which is comprised of the brain and the spinal cord. This is possible because certain cells in the brain have the same "locking system" as the T4 cells. The cells in the brain that HIV can enter are those in the white matter, the microglia, monocytes and macrophages. These cells are less important than the grey cells (neurones) which are the main cells used in thinking but damage to them can have indirect consequences on thinking. This is because they are responsible for the high-speed transmission of messages between different parts of the brain. Damage to them can therefore slow down the thinking process. More and more of these neurones are killed by HIV (and perhaps also by the production of toxins to fight against the "intruder") and they cannot normally be replaced by the body so the damage is irreversible.

What are the symptoms of ADC?

Cognitive

• forgetfulness (but distant memories often remain intact)
• difficulties with concentration and complex thought
• language difficulties (often resulting in a limitation of language to short sentences, one word answers or just speaking when spoken to)
  

Motor

• clumsiness
• slow unsteady movements
• jerky eye movements
• leg weakness
  

Behavioural

• change in personality
• loss of appetite
• withdrawal
• apathy
• lack of motivation
• inappropriate emotional response such as laughing wildly at something sad
• sharp mood swings, mania or suicidal impulses
• hallucinations

The above-mentioned symptoms of ADC may differ from person to person and more particularly from day to day and even from hour to hour. In spite of their difficulties, people with ADC are often capable of thinking clearly about many things and of expressing an opinion.

Is there any treatment for ADC?

AZT is currently used to treat people with AIDS, who may or may not have ADC. About 50% of AZT taken by mouth, penetrates the brain. Some researchers claim that taking AZT can delay ADC or even prevent it, particularly if it is taken from a relatively early stage of HIV infection. The extent of improvement is thought to depend on the extent of the damage already caused to the central nervous system. DDI is sometimes used as an alternative to AZT, but more commonly in combination. It does not seem to lead to any improvement in cognitive functioning.

It is possible to treat some of the symptoms of ADC. For example, psychostimulants may bring about improvements in people suffering from slow reactions and lithium or neuroleptics may prove effective for people who are agitated or manic.

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