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Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2013
Immunodeficiency can be caused by inherited syndromes, infections, drugs, medical conditions, pregnancy, ageing and many other factors. Immunodeficiency is defined as inadequate functioning of the immune system. The severity varies leading to different types of infection. It can occur at multiple points across the immune response. It can then lead to:
Immunodeficient people that become unwell should be carefully evaluated, and infection should be treated aggressively.
Primary immunodeficiency diseases are present from birth and persist lifelong. They are due to uncommon or rare genetic defects, and there is often a family history of the condition. The World Health Organization lists 185 different primary immunodeficiency diseases. They include:
The best known secondary or acquired immunodeficiency disease is due to infection with human immunodeficiency virus (HIV) which leads to AIDS (acquired immunodeficiency syndrome).
Human T-cell lymphotropic virus type 1 (HTLV-1) also leads to immune deficiency.
Cancers, particularly blood disorders that affect white blood cells such as leukaemia and lymphoma, may lead to severe immune deficiency.
Immunosuppression is a general dampening of the immune response, usually in response to immunosuppressive drugs. The immune response is still mounted, but it is not as efficient or efficacious.
Immunosuppressive drugs include:
Lower doses or shorter courses of systemic steroids are not considered significantly immunosuppressive. Low-dose methotrexate used for skin diseases mainly acts as an anti-inflammatory drug and is only weakly immunosuppressive.
Skin infections become more common as the number of CD4+ T-lymphocytes reduces.
Mild reduction in CD4+ T-lymphocyte count (>200) is part of normal ageing. This leads to an increased incidence of herpes zoster (shingles) and in countries where it is prevalent, old-world or classic Kaposi sarcoma.
Moderate reduction in CD4+ T-lymphocyte count (200-50) occurs in some elderly patients, newborn babies, and in primary immunodeficiency diseases. The deficient T lymphocytes tend to produce the TH2 class of cytokines, which lead to enhanced allergic reactions characterised by eosinophilic infiltrations. These include:
Severe reduction in CD4+ T-lymphocyte count (<50) usually indicates infection with HIV. It leads to unusual manifestations of infection, and infection with organisms that are normally harmless in healthy individuals. It seems that the immune system tolerates the presence of organisms that it normally fights to eradicate from the skin. Examples include:
Because the appearance of skin conditions is often different in immune suppressed individuals compared to normal, unusual conditions and infections must be considered. Tests include repeated:
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