Meningitis in HIV infection

During symptomatic HIV infection (clinical stage 3), the immune system becomes severely damaged by HIV and the individual becomes immuno-compromised. As the immune system continues to deteriorate and fails to protect the body, opportunistic infections begin to develop. Thus, symptomatic HIV infection is mainly caused by the emergence of opportunistic infections and cancers that the immune system would normally prevent.

Clinical stage 3 is also the stage where an HIV-infected person experiences unexplained severe weight loss (over 10 percent of body weight), unexplained chronic diarrhoea for longer than one month, unexplained persistent fever (intermittent or constant for longer than one month), persistent oral candidiasis, and pulmonary tuberculosis.

One of the opportunistic infections in symptomatic HIV infection (clinical stage 3) is meningitis. The meninges are the system of membranes that envelop the central nervous system. Meningitis is, therefore, the inflammation of the membranes covering the brain and the spinal cord.

There are other types of inflammation affecting various parts of the body: appendicitis (appendix), gastritis (stomach), laryngitis (larynx), otitis (ear), encephalitis (brain), and pancreatitis (pancreas).

Inflammation is the first response of the immune system to infection or irritation. It is the natural chain of events that include redness, hotness, swelling, pain and dysfunction of the organs involved. Chronic inflammation is almost always accompanied by tissue destruction, formation of an abscess or a collection of pus. When inflammation overwhelms the whole body, organ dysfunction occurs, resulting into septic shock and death.

Meningitis can be caused by infectious agents such as viruses, bacteria, fungi and protozoa. Viral meningitis is common in young children. The viruses that most commonly cause meningitis are: enteroviruses (coxsackie, echovirus, and the polio virus), the mumps virus, the Epstein-Barr virus, herpes simplex virus, and cytomegalovirus.

Bacterial meningitis is potentially life-threatening, but fortunately rare. The bacteria that cause the infection can be of any type, but the three bacteria that most commonly cause acute meningitis spread from the upper respiratory tract (the nose, throat, sinuses and lungs). These are: Neisseria meningitidis (in meningococcal meningitis), Streptococcus pneumoniae (in pneumococcal meningitis), and Haemophilus influenzae (in haemophilus meningitis).

Fungal meningitis is rare and usually only occurs in people whose immune systems have become weakened, e.g., in those with diabetes or HIV/AIDS, or very elderly people. The organisms commonly causing fungal meningitis are Cryptococcus neoformans (in cryptococcal meningitis) and Candida albicans (in candidal meningitis).

Bacterial and fungal meningitis can sometimes also be connected with a brain abscess. An abscess is a collection of inflamed or infected tissue (pus) that forms a cavity in the brain. The spread of the infection to the brain is usually via the blood (septicaemia) or occasionally from infection close to the brain (e.g. ear and sinus infections).

The first signs of meningitis may be quite general and may simply consist of: headache, high temperature, tiredness, and irritability. There may also be gastrointestinal symptoms (vomiting or diarrhoea) or respiratory symptoms (sore throat, common cold). Specific signs of meningitis include: severe headache, bright light will be uncomfortable (photophobia), neck stiffness, confusion, drowsiness, and a third of people with bacterial meningitis may have one or more fits.

Although diagnosis of meningitis as well as knowing the causative agent is important, laboratory testing takes time. Because bacterial meningitis is such an urgent issue, treatment is usually instituted before a definite diagnosis is made. When a patient is suspected of meningitis, blood culture should be drawn and empiric antibiotics started immediately.

Diagnosis of meningitis can then be carried out with examination of cerebrospinal fluid (CSF) after a lumbar puncture (LP). In medicine, a lumbar puncture (colloquially known as a spinal tap) is a diagnostic procedure that is done to collect a sample of CSF for biochemical, microbiological and cytological analysis. Many patients in Southern Africa do not take kindly to the LP. Others have even run away from hospitals for fear that they will die during the LP. If performed by trained and experienced staff, LP is a vehicle for accurate diagnosis of meningitis.

The opening pressure is noted during the LP and the CSF fluid sent for examination of white blood cells, red blood cells, glucose, protein, Gram stain, culture, and possibly latex agglutination test.

Polymerase chain reaction (PCR) has been a great advance in the diagnosis of meningitis. It has high sensitivity and specificity for many infections of the CNS, is fast, and can be done with small volumes of CSF. Even though testing is expensive, it saves cost of hospitalisation.

Increased CSF pressure can indicate congestive heart failure, cerebral edema, subarachnoid haemorrhage, hypo-osmolality resulting from haemodialysis, meningeal inflammation, purulent meningitis or tuberculous meningitis. A large number of granulocytes often heralds bacterial meningitis. Antibiotics started within four hours of lumbar puncture will not significantly affect lab results.

l KC is lecturer at the University of Namibia. Email: kchinsembu@unam.na

September 2006
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