Thyroid diseases in sub-Saharan Africa

Abstract

Thyroid gland diseases vary according to the environment. In sub-Saharan Africa, they are also influenced by population isolation and the absence of food self-sufficiency, both factors affecting the onset and persistence of iodine-deficiency goiters. More cosmopolitan diseases are now added to these thyroid disorders. Women are mainly affected (94.2%), most often with euthyroid goiters (54.7%), followed by Graves disease (13.1%), hypothyroidism (8.8%), thyroiditis (6.6%), toxic multinodular goiters (6.6 %) and unclassified goiters (10%) [Gabon]. The paucity of laboratories specializing in endocrinology and of nuclear medicine facilities, the delay in diagnosis that results in compressive or recurrent goiters, and endemic goiters are all typical in Africa. In children and adolescents, death rates increase with congenital or acquired thyroiditis as with delayed physical or mental development. In this environment, thyroiditis can also be pregnancy-related. Very recent surveys show a prevalence of endemic goiters of 28.6% in the community of Sekota, Ethiopia, 64-70% in Sahel-Sudan (population aged 10-20 years), 20-29% in KwaZulu-Natal (school children), 14.3-30.2% in Namibia (school children), 0.21% (congenital hypothyroidism or cretinism) in Plateau State, Nigeria, 55.2% at Zitenga, Burkina Faso (210 persons 0-45 years), and 10% in Hararé and Wedza, Zimbabwe (newborn TSH >10.1 microIU/mL). The prevalence of goiters is 43.6% in children emigrating from Ethiopia to Israel. Millet from semi-arid zones contains apigenin at a concentration of 150 mg/kg and luteolin at 350 mg/kg, both of which can interfere with thyroid function. The harmful effects of cassava (also known as manioc) are better known: milling cassava reduces its goitrogenic potential. In addition to iodine deficiency, selenium deficiency, and the effect of the thiocyanates in cassava, ion concentrations in soil and drinking water appear to play a role. The proportion of thyroid surgery indicated for hyperthyroidism has tripled, now accounting for 18.5% of all such operations. This disorder is found today in subjects older than 50 years, mainly from rural areas, and caused most often by Graves disease (25 of 51 cases). Graves disease in young women can cause serious problems during pregnancy; in such cases assessment of the minimal effective dose of antithyroid agents is essential. Carbimazole leads to remission in 61% of cases of Graves disease. Hypothyroidism can be auto-immune and often in patent forms because of insufficient screening in Africa: 24 cases in Dakar (1984) and 37 others noticed by us (1998). Single-nodule tumors were assessed in 89 patients in Khartoum: they were found to be simple goiters in 72% of cases, follicular adenoma in 13.5%, cancer in 13.5% (with 6 of the 12 cases follicular, 5 papillary, and 1 anaplastic). The sex ratio for thyroid cancer in Ouagadougou is 0.22, thus mainly women. It affects mainly women in their 30s. Thyroid cancer at Ibadan was found to be papillary carcinoma in 45.3% of cases; follicular forms were seen in 44.5% and this series includes 5% of medullary cancers (7 cases), with a mean age of 34 years. Already 4 other cases from Francophone sub-Saharan Africa have been noticed. Iodine deficiency is suggested to play a role because follicular cancer in southern Africa accounts for up to 55% of thyroid cancers. Thyroid cancers in Algeria are associated with low socioeconomic status and characterized by a high prevalence of cancers discovered at an advanced stage and of anaplastic carcinomas. Oral potassium iodate is recommended: 30 mg of iodate a month or 8 mg every two weeks. Iodized oil has been recommended by some authors, as well as a combination of iodine and sugar, and the iodation of drinking water; these are in addition to the proposed methods of opening up areas by new infrastructure). In conclusion, thyroid disease is due predominantly to iodine deficiency and goitrogenic products, but we also note the increasing emergence of hyperthyroidism, especially Graves disease, atrophic auto-immune hypothyroidism, and thyroid cancer. The insufficiency of infrastructure in transportation, endocrinology, and nuclear medicine are a public health challenge for the third millennium.