Lupus in AfroCaribbeans and Other Ethnic Groups

by Dr Patrick Venables, FRCP MD

Reader in Immunorheumatology and Consultant Physician

Kennedy Institute of Rheumatology, Hammersmith, London.

Source: News & Views: The Magazine of Lupus UK. Summer 1997 Number 52.

Reprinted with kind permission from Lupus UK.

How Common Is Lupus?

Lupus is a world-wide problem. As the diagnosis depends on a complex clinical and laboratory tests its frequency is only accurately known amongst some American groups and West European Caucasians. Its frequency has been estimated to be between 1:2,000 of the population in Sweden and 1:10,000 of the population in some southern European countries and parts of the United States. It is often thought that the relatively high frequency in Sweden is due to the close monitoring of the health service and that the frequency elsewhere may be higher if the patients were examined or monitored more carefully. Those who take this view generally support the idea that lupus may be equally common amongst Caucasian populations amounting to a frequency of approximately 1:2,000 which suggests that, as a serious disease, lupus ranks with other diseases such as multiple sclerosis and sickle cell anaemia as a serious world health problem.

Much less is known about the frequency of lupus in AfroCaribbeans. There have been some studies which suggest that in the west Indies lupus may be as common as 3%-4% of the population. Other studies have suggested that in America for example, lupus is between 4 and 5 times more common in blacks than it is in whites. this in turn suggests that the frequency may be approximately 1% of the black population, meaning that in this group lupus is as serious a health problem as diabetes. Although lupus is still not widely recognised amongst Western caucasian populations almost everybody coming from a large population centre in the west Indies, for example, will have heard of it, often because they know a family member or close friend who suffers from the disease. Such knowledge is also common in other tropical populations, particularly in the Philippines, the Seychelles and in tropical central America. I have also heard that in China lupus is much commoner than rheumatoid arthritis, though its exact frequency there remains unknown.

Why Is Lupus Commoner In Some Ethnic Groups?

The answer to this question remains unknown, but some clues may come from studies of lupus in Africans. Although most AfroCaribbeans in the United States and in the West Indies have their racial origins in West Africa, lupus is reported to be extremely rare there.

However, there may be problems with diagnosis, particularly as many Africa diseases eg malaria and HIV infection, may mimic lupus and in the absence of good diagnostic facilities may be misdiagnosed. Nevertheless, even in university centres in South Africa a very low frequency of the disease in the rural population is repeatedly reported, suggesting that in some way "urbanisation" has contributed to the disease. How this has occurred is not known, although one possibility could be due to a virus which is transmitted more readily through urban populations. The other possibility may be racial mixing. There have been reports, for example, that the genes associated with lupus in blacks are actually of Caucasian origin suggesting that lupus may have occurred in many patients in the West Indies as a result of racial mixing which may have occurred many generations previously. this theory could also explain the very high frequency of lupus in the Seychelles where almost every individual combines an unknown mixture of Afrocaribbean, Asian and caucasian genes. if this theory is true, increasing racial mixing may actually result in an increase in lupus world-wide in the future.

Why Is Lupus Different In Different Racial Groups?

The answer to this question is almost certainly yes. Firstly the characteristic butterfly rash over the cheeks and ridge of the nose is much less frequently seen in black lupus sufferers. It is often supposed that the dark colour of the skin makes the rash difficult to see, but in most cases I think this is an unlikely and trivial explanation. If the rash does occur it is readily appreciated by the patient as an area of thickening, sometimes itchy and often associated with pigment changes. A more likely explanation is that the rash is caused by exposure to ultraviolet light. Melanin, the dark pigment that causes the skin to go black (or brown in Caucasians after sunbathing) actually protects the delicate cells under the surface of the skin from the sun's rays, and this means that a black person in the sunlight is protected from the harmful rays of the sun. Other manifestations are also different in blacks. There is no doubt that black patients get more serious disease.

There is a higher frequency of both renal (kidney) and cerebral (brain) lupus in patients of AfroCaribbean origin and it is the opinion of almost everybody who treats patients with lupus (though I have not seen any figures to support this impression) that higher doses of steroids and more immunosuppressive drugs are necessary for AfroCaribbean patients. the frequency of one lupus antibody test called anti-Sm is much more frequent in the black population (about 40%) compared to whites (about 7%). This antibody is a marker of serious disease and presumably reflects the different pattern of involvement that is seen in AfroCaribbean. Other racial groups such as Asians or far Eastern Orientals are less well studies in this respect, although it is the general impression that these groups also do worse than Western Caucasians.

What About Treatment?

The cornerstone of treatment of lupus remains steroids. As already mentioned some ethnic groups do worse and so require more steroids to control their disease. However, one fortunate attribute of the AfroCaribbean race is that their bones are genetically built much more strongly, so one of the most feared side-effects of steroids, osteoporosis (brittle bones) is not so much of a problem in blacks compared to whites. However in Asians who have relatively "thin" bones, it may be a more serious problem. Asians tend to eat a diet which is low in vitamin D and calcium supplementation should always be thought about. Another problem with steroids and lupus is high blood pressure. High blood pressure is particularly prevalent among female AfroCaribbeans and this on top of lupus and steroids can be a serious problem in treatment, particularly as prolonged high blood pressure can eventually contribute to kidney damage.

What Is Being Done About Lupus In Ethnic Minorities?

Many patients with lupus feel, quite reasonably, that their disease is under-recognised, under-diagnosed, under-treated and under-researched. This is certainly true of the past and in some cases continues to be a serious problem. However, lupus has now become a major research initiative in several Western European and American institutions, for example, the National Institute of Health in Washington, the largest grant awarding body in the United States, has dedicated an annual budget of over 30 million specifically for lupus research. Even in the UK, where rheumatoid arthritis research is probably about 10 times commoner than lupus, the amount of money in rheumatoid arthritis research is only double that of money devoted to lupus and other connective tissue diseases. This research takes two forms. one is the "clinical interface" where treatments, either traditional such as steroids or new treatments, are being carefully evaluated in controlled clinical trials and secondly more basic research where people are looking at the fundamentally scientific mechanisms of disease. Obviously, the second form of research will not have any benefit in the short term, though it is quite possible that in years to come, with greater understanding of the disease, we may be nearer to a cure.