Sarcoidosis is a disease that has been known for more than a century. The classic description, made by Jonathan Hutchinson in 1877, of a 55-year-old man presenting non-painful skin plaque with bumps and eventually dying from renal failure, without a doubt describes a case of sarcoidosis. This disease may manifest as skin lesions, arthralgia and disorders of calcium metabolism, leading to nephrocalcinosis and renal failure. Since the time of Hutchinson, various descriptions and "new" clinical/histopathological findings have been analyzed. Such findings are currently thought to be different presentations of sarcoidosis. Over this considerable length of time, much has been learned about this disease, although there is still much to be discovered.(1-2) Among the various enigmas found in the body of knowledge is the etiology of the disease itself. This has certainly made it difficult to clearly visualize its true parameters. The core knowledge of the disease is well structured from various points of view, including those of epidemiology, clinical findings, laboratory testing, imaging, immunology and treatment. However, its presentation frequently varies in peripheral, sometimes ample, ways, as does the knowledge of the disease.

It is currently known that the disease is distributed worldwide, albeit in a less than uniform manner. Some areas of the planet present higher incidence rates than do others. The true cause of such differences remains a mystery. However, it could be related to, among other factors, any of the following: the fact that the etiologic agent is as yet unknown, and the consequent lack of a specific diagnostic test; lesser or greater diagnostic capacity in the various regions; variation in the presentation and, consequently, in the identification of cases; and a race-based difference in susceptibility.(1) Therefore, epidemiological studies always contribute to improving and expanding knowledge of diseases such as sarcoidosis.

Cases of sarcoidosis were first reported in Europe, with varying rates of incidence and prevalence. The highest prevalence, 64/100,000 inhabitants, is found in Sweden, compared with 26.7/100,000 in Norway, and the prevalence in Finland is very low. In the United Kingdom, a radiological study of 3 million individuals revealed that the prevalence of pulmonary sarcoidosis was 20/100,000 inhabitants, whereas Spain has one of the lowest rates of sarcoidosis prevalence in the region. In the USA, the annual incidence was reported to be 35.5/100,000 African-Americans and 10.9/100,000 Caucasians. In Canada, a radiological study revealed a prevalence of 10.5/100,000 inhabitants, despite the fact that the disease is rare among Eskimos and North American Indians. In Asian countries, where the prevalence was initially considered low, an ever-increasing number of cases of sarcoidosis have been reported, and interest in conducting studies of the disease has therefore grown. Prevalence rates ranging from less than 10/100,000 inhabitants to 20/100,000 inhabitants have been reported in Japan, China, Taiwan, Korea and Malaysia. In South Africa, the disease appears to be, as in the USA, more common among blacks (10-20/100,000) than among whites (less than 10/100,000).

However, in the African continent as a whole, there have only been
sporadic reports of cases.(3) In Central and South America, there have been few published studies investigating the prevalence of sarcoidosis, although a high prevalence has been reported in Uruguay.(4) In Brazil, more than twenty years ago, my father, Prof. Newton Bethlem, estimated the prevalence of the disease to be less than 10/100,000 inhabitants.(5) Since our country is continental in dimension, a considerable, healthy, amount of racial miscegenation exists. Unfortunately, this also contributes to a high prevalence of infectious and contagious diseases, many of a granulomatous nature, thereby making epidemiological studies, and other types of studies, extremely important in the region. Certainly, through stimulating interest in the disease its identification and its study in Brazil, we will not only draw closer to determining its true prevalence, incidence and presentation in our region but will also be able to contribute, in an incisive way, to increasing knowledge of the disease. Brazilian case-series studies, such as those conducted by Prof. Luis Carlos Correa (a well known scholar in the area of sarcoidosis) and included in this issue of the journal,(6) contribute greatly to clarifying the view of sarcoidosis in Brazil.


REFERENCES

1. Hunninghake GW, Costabel U, Ando M, Baughman R, Cordier JF, Du Bois R, et al. ATS/ERS/WASOG statement on sarcoidosis. American Thoracic Society/European Respiratory Society/World Association of Sarcoidosis and other granulomatous disorders. Sarcoidosis Vasc Diffuse Lung Dis. 1999;16(2):149-73.
2. Sharma OP. Sarcoidosis: a worldwide phenomenon. Sarcoidosis. 1984;1(1):11-5.
3. James DG, Hosoda Y. Epidemiology in sarcoidosis and other granulomatous disorders. New York: Marcel Dekker; 1994. (Lung biology in health and disease)
4. Purriel P, Navarrete E. Epidemiology of sarcoidosis in Uruguai and other countries of Latin America. Am Rev Respir Dis. 1961;84(5 Pt 2):155-61.
5. Bethlem NM. Epidemiology of sarcoidosis in Brazil. Sarcoidosis. 1985;2:162.
6. Corrêa da Silva LC, Hertz FT, Cruz DB, Caraver F, Fernandes JC, Fortuna FP, et al. Sarcoidose no sul do Brasil: Estudo de 92 pacientes. J Bras Pneumol. 2005;31(5)398-406.

Eduardo Pamplona Bethlem
Adjunct Professor of Pulmonology at the Universidade Federal do Estado do Rio de Janeiro (UNIRIO, Federal University of the State of Rio de Janeiro), Rio de Janeiro, Rio de Janeiro, Brazil