IntroductionThyroid disorders are thedisruption in the systematic functioning of the thyroid gland. These disordersmay be benign or malignant affecting the structure, function or both of thethyroid gland. The manifestations of thyroiddisorders are determined by the dietary iodine availability. The world’spopulation living in iodine deficient areas is 35 percent.1 In Africa, dietary iodine availability is themajor determinant of thyroid pathology.
2 In areas where the daily iodine intake is?50 mg, goitre is usually endemic, and when the daily intake falls to ?25 mg,congenital hypothyroidism is seen. The prevalence of goitre in areas of severeiodine deficiency can be as high as 80%.3 The challenge of civil warsin many regions of Africa in the past, the attention shift to communicablediseases by the various governments in the region, poverty and instability inthe polity contributed to the delay in eradicating iodine deficiency in Africa.4 In recent years,there has been a marked improvement in iodine nutrition through salt iodinationin the African continent.5 Thethyroid disorders that are frequently noted in Africa include iodine deficiencydisorders (goitres, hypothyroidism and mental retardation), hypothyroidism,thyrotoxicosis (thyroid or non-thyroid causes) and thyroid malignancies.2,6In this article, we lookedat the thyroid disorders in Africa and where Africa currently stands. MethodWe used the Pubmed, Medlineand Googles scholar as the search engine. The search term was ‘Africa’ used invarious combinations with thyroid gland, iodine deficiency disorders, goitre,hyperthyroidism, hypothyroidism, autoimmune thyroid disorders and thyroidcancers.
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We also used names of different countries in Africa as search term.Available articles on thyroid disorder in Africa published until 2017 werereviewed. DiscussionIodinedeficiency disorders (IDD)In Africa, dietary iodinedeficiency is the major determinant of thyroid pathology. It results in a spectrumof iodine deficiency disorders.2 Iodine deficiency isdefined as a median urinary iodine concentration less than 50 ?g/L in apopulation.
5 Of these persons,30–70% have goiter and 1–10% have cretinism. Eight percent of newborns fromsub-Saharan Africa are unprotected from learning disabilities resulting fromiodine deficiency related disorders according to UNICEF estimate.5 The pattern ofthyroid disorders in a population is dependent on environmental iodine intake.7 Iodine deficiencydisorders abound in areas with inadequate iodine intake while autoimmunethyroid disorders are rare in iodine deficiency but become prevalent withtransition to iodine sufficiency.7 These disorders includegoitres, hypothyroidism,mental retardation, Iodine-induced hyperthyroidism.7Endemic goitersIn Africa the most commongoitres are those due to dietary iodine deficiency.
7 The thyroid gland isenlarged in endemic goitre. A contributory factor to iodine deficiency includeslocation of the affected people. Majority of affected individuals reside inmountainous regions where iodine is leached from the soil.
7 Iodine deficiency isfurther worsened by goitrogens (substances that suppress the function of thethyroid gland by interfering with iodine uptake) present in some staple foodeaten in Africa. Poor processing of cassava, a staple eaten in Africa that isrich in thiocyanate which is a goitrogen, contributes to the development ofiodine deficiency.8 Selenium deficiencyhas also been reported to be a contributory factor in the occurrence of endemicgoiter in Africa or persistence of endemic goiter in iodine deficient areas evenafter correcting for iodine deficiency.
9 The prevalence of endemic goitre in Africavaries from 1% – 90% as shown in table 1.EndemiccretinismCretinism is the mostextreme manifestation of IDD. Cretinism can be divided into neurologic andmyxedematous subtypes. These subtypes have considerable clinical overlap.
19 Endemic cretinism isvery prevalent in Central Africa occurring in 1.2% – 6% of the population.19 Neurologic cretinismis thought to be caused by severe IDD with hypothyroidism in the mother duringpregnancy and is characterized by mental retardation, abnormal gait, anddeaf-mutism, but not by goiter or hypothyroidism in the child.20 Myxedematouscretinism is considered to result from iodine deficiency and hypothyroidism inthe fetus during late pregnancy or in the neonatal period, resulting in mentalretardation, short stature, goiter, and hypothyroidism.
20 The myxedematouscretinism is common in the Central Africa and hypothyroidism is seen in as muchas a quarter of children in endemic areas.21 This pattern contrastswith other parts of the world where the neurological variety, characterized bymental deficiency, deaf mutism and spastic diplegia prevails.22 Reports on endemiccretinism in the twenty-first century Africa is almost not existent inliterature and this may be largely due to widespread iodization programs in theAfrican continent.
Iodine-inducedThyrotoxicosisIodine-inducedthyrotoxicosis is another subset of IDD. It occurs when individuals who arechronically iodine deficient are exposed to sharp rise in iodine intake.23 It is also worthy tonote that it occurs in people with longstanding thyroid nodules. The thyroidnodule may undergo toxic change leading to thyrotoxicosis with resultantcomplication of cardiac arrhythmias and cardiac failure.23 Two reports fromZaire and Zimbabwe showed an increase in thyrotoxicosis following introductionof iodized salt in both countries. Majority of these people have nodular goitreand are iodine deficient.24 The thyrotoxicosisnoted in this group of people was however transient and it is limited to thoseregions of Africa.
Thyrocytesin nodules often become insensitive to TSH control, and if iodine supply issuddenly increased, these autonomous nodules might overproduce thyroid hormone.25 The salt iodization wasreduced in the region to minimize the morbidity and mortality consequent uponintroducing iodized salt at a standards recommended dose.24Autoimmunethyroid diseaseAutoimmune disease affectsthe thyroid more than any other organ.26 A rapid increase in iodine intake canenhance thyroid autoimmunity possibly through increasing antigenicity ofthyroglobulin.27 Autoimmune thyroid disease(AITD) encompasses a closely related spectrum of disorders, representing twoclusters of pathogenic mechanisms. These are Hashimoto’s disease and Graves’disease. Hashimoto’s disease (chronic autoimmune thyroiditis and autoimmunehypothyroidism) and post-partum thyroiditis/painless thyroiditis share apredominately T cell-mediated autoimmunity, while Graves’ disease ischaracterized by a primarily humoral response and the presence of anti-thyroidstimulating hormone (TSH) receptor antibodies.28 Serum thyroid peroxidase(TPO) and thyroglobulin (Tg) antibodies formation is the hallmark of all formsof AITD.
Underlying autoimmunity without clinical autoimmune disease isdiagnosed by the presence of these antibodies.29 The overallprevalence of AITD in Africa is 1.2% – 9.9%.
6 Hashimoto’s diseaseThis is one of the spectraof autoimmune hypothyroidism. Others include primary myxoedema and postpartumthyroiditis. It is very commonly seen in iodine sufficient countries.3 Hashimoto’s diseaseis not as prevalent as Grave’s disease in Africa.
30 In Hashimoto’sthyroiditis, the disorder is directed against thyroid antigens and it is themost common cause of hypothyroidism.31 Hashimoto’sthyroiditis is more prevalent in areas with a high dietary iodized salt intake,and smoking increases the risk.32 The most commonpresentation is thyroid gland atrophy. Goitre can also be seen at presentationin some individuals. Hashimoto’s thyroiditis is associated with other endocrinediseases in polyglandular autoimmune failure syndrome (Addison’s disease, type1 diabetes mellitus, and hypogonadism).
32 The diagnosis ismade by clinical features, elevated TSH, low thyroid hormone, and the presenceof antithyroid peroxidase antibodies (anti-TPO).31,32Grave’s diseaseThis is another form ofAITD. It more prevalent in Africa than the Hashimoto thyroiditis.6 Graves’ disease,unlike in the past, is now frequently reported in Africa.33 In a study fromSouth Africa, a 60% increase in its incidence was reported over an 11-yearperiod.
34 This is mostly seenin the urban residents who are iodine replete. Majority of these urbanresidents have recently migrated from iodine deficient areas.34 Graves’ disease involvesthe binding of autoantibodies to TSH receptor which leads to stimulation of thethyroid gland. It is the most common cause of thyrotoxicosis. Receptoractivation stimulates thyrocyte growth and function.34 The presentation ofGrave’s disease is typically that of thyrotoxicosis in most part of Africa.Patients who have Grave’s disease sometimes can present with complications.Grave’s ophthalmopathy is the most common complication reported.
35 Cardiaccomplications and myopathy were noted more in black South Africans compared to white.35 The frequency ofthyrotoxic heart disease varied from 42% to 46.6% in some reports from Nigeriaand Togo.36,37Othercauses of thyroid dysfunctionTuberculosisThe association betweenthyroid dysfunction and tuberculosis has not been well studied in Africa. Post et al in a study involving 50 patientswith active tuberculosis reported sick euthyroid syndrome in 92% of thepatients.38 A case report fromSomalia of a man with thyroid tuberculosis showed the man was euthyroid eventhough he has a goiter.
39 Kaplan et al in another cross-sectionalstudy done in South Africa reported a prevalence of sick euthyroid syndrome of42% among 40 patients with active TB.40Drug induced thyroiddysfunctionLittle is known about thefrequency of thyroid dysfunction (TD) associated with amiodarone therapy inAfrica. Amiodarone is a potent antiarrhythmic agent that is associated with newonset thyroid dysfunction. A South Africa study recorded a high incidence ofnew onset thyroid dysfunction (TD) in a subset of 163 patients after a medianduration of 369 days of treatment with amiodarone for cardiac arrhythmias. The percentageof the patients that developed new onset TD was 27.6% of which subclinicalhypothyroidism and subclinical hyperthyroidism were the commonly documented TD.41ThyroidmalignancyThyroid cancer is thecommonest occurring endocrine cancer.42 Follicular andpapillary cancers are well differentiated cancers of the thyroid glandoccurring worldwide.
43 The histology ofthyroid cancers in a population is dependent on the ambient iodine intake.44 A high proportion ofaggressive follicular and anaplastic tumours are seen in iodine deficiencywhile the more benign papillary type is common in iodine-rich populations.44 Iodination programhas altered the pattern of thyroid cancers in the African sub region.
Earlyreports indicates a predominance of follicular thyroid cancer.45 This pattern hasprevailed over the decades, suggesting persisting iodine deficiency. More ofpapillary thyroid cancers are now reported from most parts of African region.45 Improvement iniodination status of most countries will account for this change in pattern. IodineNutrition in AfricaThe elimination of iodine deficiency and its seriousconsequences, called the iodine deficiency disorders (IDD), are among thehealth priorities of most countries in the world. Saltiodization programs in approximately 150 countries have markedly improved theglobal iodine nutritional status over the past decade.
This is reflected in thedecrease in the number of iodine-deficient countries worldwide from 54 in 2003to 47 in 2007 and then to 32 in 2011.54 Inthe last three decades, elimination of iodine deficiency has been very slow inmost African countries. Structured programs aimed at eradicating iodinedeficiency were not put in place by most African governments. In countries orregions where such program exists, the approach is not coordinated. Hence thelittle results seen in the improvement of iodine intake. The regional burden of iodine deficiencyin Africa compared to other regions is further emphasized by the finding thatseven of the top 10 iodine-deficient countries with the greatest numbers ofschool-age children (SAC) with insufficient iodine intake in 2011 are fromAfrica.55 These countries, ranked by the numberof deficient SAC, were: Ethiopia, Sudan, Algeria, Angola, Mozambique, Ghana, andMorocco.
54 The household coverage of iodized salt bycountry varies on the African continent. Countries with successful iodized saltprograms achieving a household coverage of more than 90% are: Burundi, Kenya,Nigeria, Uganda, Tunisia, Namibia, Zimbabwe, and Libya.54 Countries with promising householdcoverage rates of between 80 and 90% are: Rwanda, Sao Tome & Principe, Coted’Ivoire, Lesotho, Comoros, the Congo Brazaville, and Tanzania.54The population atrisk of developing iodine deficiency disorders still remain very high even withcoverage achieved thus far.55 Within iodine sufficientAfrican countries, pockets of severe deficiency persist and vulnerablepopulation sub-groups like neonates, toddlers and pregnant women continue to bein danger of iodine deficiency disorders.
56,57 Nonetheless, theprogress in recent years clearly indicates that iodine sufficiency is trulywithin reach in Africa.Diagnosisof thyroid disordersThe paucity of laboratories specializing in endocrinology isa serious problem seen in many African countries. Indiagnosing thyroid disorder, the diagnostic techniques employed includeimmunoassays, serology, ultrasonography, fine needle aspiration cytology (FNAC)and histopathological techniques for the evaluation of thyroid nodules,computed tomographic (CT) scans and magnetic resonance imaging (MRI). Thesediagnostic techniques are not widely available. Where these facilities areavailable, it is out of reach for most of the patients because they paysout-of-pocket.
6 The deployment ofnuclear medicine, both for diagnosis and management of thyroid disorders, isalso not widely available in most African countries. The use of nuclearmedicine is more prominent in the South African sub region. There are fewreports from the West African sub region specifically Nigeria and Sierra Leoneon the use of nuclear medicine in the diagnosis of hyperthyroidism.58,59Treatmentof thyroid disordersIn most Africancountries, the treatment modalities that are commonly employed in the treatmentof thyrotoxicosis are pharmacotherapy, using the thionamides, and surgery.
In afollow up of patients treated with thionamides in Nigeria, the remission ratewas noted to be 61% and this was associated with small-sized goiters andshorter duration of illness.60 Surgery is anothertreatment option in the management of simple goiters, toxic goiters, nodulargoiters and thyroid carcinoma. There is hardly information on the outcome ofthyroid disorders in Africa and this is largely attributable to the virtualabsence of thyroid registries in the continent.6ConclusionThyroid disorder inAfrica has evolved over a period of time.
Most of the disorders are stillstrongly linked with regional iodine status. However recent developments inAfrica have shown that most nations in Africa have more than 80% iodinesufficiency with some having above 90% iodination. Diagnosis of thyroiddisorders still poses a big challenge in most African countries due to noavailability of specialized endocrine laboratory and where these modalities arepresent, it not accessible to the patients because of the structure of thehealthcare system which is paid for out of pocket. The use of nuclear modalityto diagnose and treat thyroid disorders is highly underutilized. Treatmentmodalities remain pharmacotherapy and surgical intervention.
The absence ofthyroid registry in the African sub region makes it difficult to properlydetermine to scope and burden of thyroid disorder in Africa.