TreatmentUpdate41: Vol. 4, No. 1 - March, 1993
Sean Hosein

The body uses fragments of red blood cells called platelets to help blood clot and stop bleeding. When the number of platelets falls below the normal range people can be at risk for uncontrolled bleeding and other complications. ITP (idiopathic thrombocytopenic purpura) is a condition where the immune system attacks and destroys platelets.

ITP: Who Gets It?

A recent study of over 700 subjects in Amsterdam has documented cases of ITP both in HIV-infected and non-HIV-infected people. Men who did not have HIV infection were less likely to develop ITP than men who had HIV infection. Thus, 9% of non-HIV-infected subjects who were injection drug users and 3% of those who had sex with other men had lower-than-normal levels of platelets. When the researchers looked at data from subjects with HIV infection the incidence of ITP increased. Among subjects infected with HIV and who were drug users the incidence of ITP was 37%. The equivalent proportion among men who had sex with men was 16%.

Why Platelet Problems Happen

Researchers do not know the exact cause of ITP in people with HIV infection. Some researchers in Vancouver think that low platelet levels are a result of viral infection. Some viral infections can shorten platelet survival, impair platelet production or both. Results from some studies suggest that the interaction between HIV and the immune system may play a role in ITP.

* Attacks by antibodies. For instance, parts of HIV may "resemble" parts of the body, including platelets. Antibodies produced against HIV also may attack platelets because of this resemblance.

* Immune complexes. An immune complex is a combination of an antibody and something it has attacked such as viruses, bacteria, fungi and so on. Platelets that are coated with immune complexes are attacked and destroyed by the immune system.

Several therapies are used to help treat ITP; some are listed in TreatmentUpdate 25. Not all therapies work in every person. Indeed, one of the problems with ITP in general is that for some people a particular therapy will work for several months and then platelet levels again fall below normal values (personal communication, D. MacFadden, MD, PhD). The term platelet survival refers to the time a platelet remains in circulation in the blood. Although AZT can temporarily increase the platelet count, the platelets do not "survive" for an increased time span. Two other possible therapies for ITP are low-dose radiation and vitamin C.

References:

1. Kaptkin S, Nardi MA and Kouri YH. Internal-image, idiotype HIV-1 gp120 antibody in human immunodeficiency virus type 1 (HIV-1) seropositive individuals with thrombocytopenia. Proceedings of the National Academy of Sciences USA 1992;89: 1487-1489.

2. Beuaieb A, Fromont P, Louache F, et al. Presence of crossreactive antibody between human immunodeficiency virus (HIV) and platelet glycoproteins in HIV-related immune thrombocytopenic purpura. Blood 1992;80(1):162-169.

3. Ballem PJ, Belzberg A, Devine DV, et al. Kinetic studies of the mechanism of thrombocytopenia in patients with human immunodeficiency virus infection. New England Journal of Medicine 1992:327(25):1779-1784.

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Copyright © 1993 - TreatmentUpdate. Reproduced with permission. Reproduction of this article (other than one copy for personal reference) must be cleared through the Editor, The Canadian AIDS Treatment Information Exchange, 555 Richmond St. West, Suite 505, Box 1104, Toronto, ON, M5V 3B1 • Phone: 416-203-7122 • Toll Free: 1-800-263-1638 • Fax: 416-203-8284  http://www.catie.ca