THYROID from learning disabilities resulting from iodine deficiency

THYROID
DISORDERS IN AFRICA: WHERE DO WE STAND?

Introduction

Thyroid disorders are the
disruption in the systematic functioning of the thyroid gland. These disorders
may be benign or malignant affecting the structure, function or both of the
thyroid gland. The manifestations of thyroid
disorders are determined by the dietary iodine availability. The world’s
population living in iodine deficient areas is 35 percent.1 In Africa, dietary iodine availability is the
major 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 severe
iodine deficiency can be as high as 80%.3 The challenge of civil wars
in many regions of Africa in the past, the attention shift to communicable
diseases by the various governments in the region, poverty and instability in
the 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 iodination
in the African continent.5 The
thyroid disorders that are frequently noted in Africa include iodine deficiency
disorders (goitres, hypothyroidism and mental retardation), hypothyroidism,
thyrotoxicosis (thyroid or non-thyroid causes) and thyroid malignancies.2,6

In this article, we looked
at the thyroid disorders in Africa and where Africa currently stands.

 

Method

We used the Pubmed, Medline
and Googles scholar as the search engine. The search term was ‘Africa’ used in
various combinations with thyroid gland, iodine deficiency disorders, goitre,
hyperthyroidism, hypothyroidism, autoimmune thyroid disorders and thyroid
cancers. We also used names of different countries in Africa as search term.
Available articles on thyroid disorder in Africa published until 2017 were
reviewed.

Discussion

Iodine
deficiency disorders (IDD)

In Africa, dietary iodine
deficiency is the major determinant of thyroid pathology. It results in a spectrum
of iodine deficiency disorders.2 Iodine deficiency is
defined as a median urinary iodine concentration less than 50 ?g/L in a
population.5 Of these persons,
30–70% have goiter and 1–10% have cretinism. Eight percent of newborns from
sub-Saharan Africa are unprotected from learning disabilities resulting from
iodine deficiency related disorders according to UNICEF estimate.5 The pattern of
thyroid disorders in a population is dependent on environmental iodine intake.7 Iodine deficiency
disorders abound in areas with inadequate iodine intake while autoimmune
thyroid disorders are rare in iodine deficiency but become prevalent with
transition to iodine sufficiency.7 These disorders include
goitres, hypothyroidism,
mental retardation, Iodine-induced hyperthyroidism.7

Endemic goiters

In Africa the most common
goitres are those due to dietary iodine deficiency.7 The thyroid gland is
enlarged in endemic goitre. A contributory factor to iodine deficiency includes
location of the affected people. Majority of affected individuals reside in
mountainous regions where iodine is leached from the soil.7 Iodine deficiency is
further worsened by goitrogens (substances that suppress the function of the
thyroid gland by interfering with iodine uptake) present in some staple food
eaten in Africa. Poor processing of cassava, a staple eaten in Africa that is
rich in thiocyanate which is a goitrogen, contributes to the development of
iodine deficiency.8 Selenium deficiency
has also been reported to be a contributory factor in the occurrence of endemic
goiter in Africa or persistence of endemic goiter in iodine deficient areas even
after correcting for iodine deficiency.9  The prevalence of endemic goitre in Africa
varies from 1% – 90% as shown in table 1.

Endemic
cretinism

Cretinism is the most
extreme manifestation of IDD. Cretinism can be divided into neurologic and
myxedematous subtypes. These subtypes have considerable clinical overlap.19 Endemic cretinism is
very prevalent in Central Africa occurring in 1.2% – 6% of the population.19 Neurologic cretinism
is thought to be caused by severe IDD with hypothyroidism in the mother during
pregnancy and is characterized by mental retardation, abnormal gait, and
deaf-mutism, but not by goiter or hypothyroidism in the child.20 Myxedematous
cretinism is considered to result from iodine deficiency and hypothyroidism in
the fetus during late pregnancy or in the neonatal period, resulting in mental
retardation, short stature, goiter, and hypothyroidism.20 The myxedematous
cretinism is common in the Central Africa and hypothyroidism is seen in as much
as a quarter of children in endemic areas.21 This pattern contrasts
with other parts of the world where the neurological variety, characterized by
mental deficiency, deaf mutism and spastic diplegia prevails.22 Reports on endemic
cretinism in the twenty-first century Africa is almost not existent in
literature and this may be largely due to widespread iodization programs in the
African continent.

Iodine-induced
Thyrotoxicosis

Iodine-induced
thyrotoxicosis is another subset of IDD. It occurs when individuals who are
chronically iodine deficient are exposed to sharp rise in iodine intake.23 It is also worthy to
note that it occurs in people with longstanding thyroid nodules. The thyroid
nodule may undergo toxic change leading to thyrotoxicosis with resultant
complication of cardiac arrhythmias and cardiac failure.23 Two reports from
Zaire and Zimbabwe showed an increase in thyrotoxicosis following introduction
of iodized salt in both countries. Majority of these people have nodular goitre
and are iodine deficient.24 The thyrotoxicosis
noted in this group of people was however transient and it is limited to those
regions of Africa. Thyrocytes
in nodules often become insensitive to TSH control, and if iodine supply is
suddenly increased, these autonomous nodules might overproduce thyroid hormone.25 The salt iodization was
reduced in the region to minimize the morbidity and mortality consequent upon
introducing iodized salt at a standards recommended dose.24

Autoimmune
thyroid disease

Autoimmune disease affects
the thyroid more than any other organ.26 A rapid increase in iodine intake can
enhance thyroid autoimmunity possibly through increasing antigenicity of
thyroglobulin.27  Autoimmune thyroid disease
(AITD) encompasses a closely related spectrum of disorders, representing two
clusters of pathogenic mechanisms. These are Hashimoto’s disease and Graves’
disease. Hashimoto’s disease (chronic autoimmune thyroiditis and autoimmune
hypothyroidism) and post-partum thyroiditis/painless thyroiditis share a
predominately T cell-mediated autoimmunity, while Graves’ disease is
characterized by a primarily humoral response and the presence of anti-thyroid
stimulating hormone (TSH) receptor antibodies.28 Serum thyroid peroxidase
(TPO) and thyroglobulin (Tg) antibodies formation is the hallmark of all forms
of AITD. Underlying autoimmunity without clinical autoimmune disease is
diagnosed by the presence of these antibodies.29 The overall
prevalence of AITD in Africa is 1.2% – 9.9%.6

 

Hashimoto’s disease

This is one of the spectra
of autoimmune hypothyroidism. Others include primary myxoedema and postpartum
thyroiditis. It is very commonly seen in iodine sufficient countries.3 Hashimoto’s disease
is not as prevalent as Grave’s disease in Africa.30 In Hashimoto’s
thyroiditis, the disorder is directed against thyroid antigens and it is the
most common cause of hypothyroidism.31 Hashimoto’s
thyroiditis is more prevalent in areas with a high dietary iodized salt intake,
and smoking increases the risk.32 The most common
presentation is thyroid gland atrophy. Goitre can also be seen at presentation
in some individuals. Hashimoto’s thyroiditis is associated with other endocrine
diseases in polyglandular autoimmune failure syndrome (Addison’s disease, type
1 diabetes mellitus, and hypogonadism).32 The diagnosis is
made by clinical features, elevated TSH, low thyroid hormone, and the presence
of antithyroid peroxidase antibodies (anti-TPO).31,32

Grave’s disease

This is another form of
AITD. 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 from
South Africa, a 60% increase in its incidence was reported over an 11-year
period.34 This is mostly seen
in the urban residents who are iodine replete. Majority of these urban
residents have recently migrated from iodine deficient areas.34 Graves’ disease involves
the binding of autoantibodies to TSH receptor which leads to stimulation of the
thyroid gland. It is the most common cause of thyrotoxicosis. Receptor
activation stimulates thyrocyte growth and function.34 The presentation of
Grave’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 Cardiac
complications and myopathy were noted more in black South Africans  compared to white.35 The frequency of
thyrotoxic heart disease varied from 42% to 46.6% in some reports from Nigeria
and Togo.36,37

Other
causes of thyroid dysfunction

Tuberculosis

The association between
thyroid dysfunction and tuberculosis has not been well studied in Africa. Post et al in a study involving 50 patients
with active tuberculosis reported sick euthyroid syndrome in 92% of the
patients.38 A case report from
Somalia of a man with thyroid tuberculosis showed the man was euthyroid even
though he has a goiter.39 Kaplan et al  in another cross-sectional
study done in South Africa reported a prevalence of sick euthyroid syndrome of
42% among 40 patients with active TB.40

Drug induced thyroid
dysfunction

Little is known about the
frequency of thyroid dysfunction (TD) associated with amiodarone therapy in
Africa. Amiodarone is a potent antiarrhythmic agent that is associated with new
onset thyroid dysfunction. A South Africa study recorded a high incidence of
new onset thyroid dysfunction (TD) in a subset of 163 patients after a median
duration of 369 days of treatment with amiodarone for cardiac arrhythmias. The percentage
of the patients that developed new onset TD was 27.6% of which subclinical
hypothyroidism and subclinical hyperthyroidism were the commonly documented TD.41

Thyroid
malignancy

Thyroid cancer is the
commonest occurring endocrine cancer.42 Follicular and
papillary cancers are well differentiated cancers of the thyroid gland
occurring worldwide.43 The histology of
thyroid cancers in a population is dependent on the ambient iodine intake.44 A high proportion of
aggressive follicular and anaplastic tumours are seen in iodine deficiency
while the more benign papillary type is common in iodine-rich populations.44 Iodination program
has altered the pattern of thyroid cancers in the African sub region. Early
reports indicates a predominance of follicular thyroid cancer.45 This pattern has
prevailed over the decades, suggesting persisting iodine deficiency. More of
papillary thyroid cancers are now reported from most parts of African region.45 Improvement in
iodination status of most countries will account for this change in pattern.

 

Iodine
Nutrition in Africa

The elimination of iodine deficiency and its serious
consequences, called the iodine deficiency disorders (IDD), are among the
health priorities of most countries in the world. Salt
iodization programs in approximately 150 countries have markedly improved the
global iodine nutritional status over the past decade. This is reflected in the
decrease in the number of iodine-deficient countries worldwide from 54 in 2003
to 47 in 2007 and then to 32 in 2011.54 In
the last three decades, elimination of iodine deficiency has been very slow in
most African countries. Structured programs aimed at eradicating iodine
deficiency were not put in place by most African governments. In countries or
regions where such program exists, the approach is not coordinated. Hence the
little results seen in the improvement of iodine intake. The regional burden of iodine deficiency
in Africa compared to other regions is further emphasized by the finding that
seven of the top 10 iodine-deficient countries with the greatest numbers of
school-age children (SAC) with insufficient iodine intake in 2011 are from
Africa.55 These countries, ranked by the number
of deficient SAC, were: Ethiopia, Sudan, Algeria, Angola, Mozambique, Ghana, and
Morocco.54 The household coverage of iodized salt by
country varies on the African continent. Countries with successful iodized salt
programs achieving a household coverage of more than 90% are: Burundi, Kenya,
Nigeria, Uganda, Tunisia, Namibia, Zimbabwe, and Libya.54 Countries with promising household
coverage rates of between 80 and 90% are: Rwanda, Sao Tome & Principe, Cote
d’Ivoire, Lesotho, Comoros, the Congo Brazaville, and Tanzania.54

The population at
risk of developing iodine deficiency disorders still remain very high even with
coverage achieved thus far.55 Within iodine sufficient
African countries, pockets of severe deficiency persist and vulnerable
population sub-groups like neonates, toddlers and pregnant women continue to be
in danger of iodine deficiency disorders.56,57 Nonetheless, the
progress in recent years clearly indicates that iodine sufficiency is truly
within reach in Africa.

Diagnosis
of thyroid disorders

The paucity of laboratories specializing in endocrinology is
a serious problem seen in many African countries. In
diagnosing thyroid disorder, the diagnostic techniques employed include
immunoassays, 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). These
diagnostic techniques are not widely available. Where these facilities are
available, it is out of reach for most of the patients because they pays
out-of-pocket.6 The deployment of
nuclear medicine, both for diagnosis and management of thyroid disorders, is
also not widely available in most African countries. The use of nuclear
medicine is more prominent in the South African sub region. There are few
reports from the West African sub region specifically Nigeria and Sierra Leone
on the use of nuclear medicine in the diagnosis of hyperthyroidism.58,59

Treatment
of thyroid disorders

In most African
countries, the treatment modalities that are commonly employed in the treatment
of thyrotoxicosis are pharmacotherapy, using the thionamides, and surgery. In a
follow up of patients treated with thionamides in Nigeria, the remission rate
was noted to be 61% and this was associated with small-sized goiters and
shorter duration of illness.60 Surgery is another
treatment option in the management of simple goiters, toxic goiters, nodular
goiters and thyroid carcinoma. There is hardly information on the outcome of
thyroid disorders in Africa and this is largely attributable to the virtual
absence of thyroid registries in the continent.6

Conclusion

Thyroid disorder in
Africa has evolved over a period of time. Most of the disorders are still
strongly linked with regional iodine status. However recent developments in
Africa have shown that most nations in Africa have more than 80% iodine
sufficiency with some having above 90% iodination. Diagnosis of thyroid
disorders still poses a big challenge in most African countries due to no
availability of specialized endocrine laboratory and where these modalities are
present, it not accessible to the patients because of the structure of the
healthcare system which is paid for out of pocket. The use of nuclear modality
to diagnose and treat thyroid disorders is highly underutilized. Treatment
modalities remain pharmacotherapy and surgical intervention. The absence of
thyroid registry in the African sub region makes it difficult to properly
determine to scope and burden of thyroid disorder in Africa.

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