Q66: Endocrinology: PLAB/UK(MLA)/AKT Exam style question
Today we will discuss another Q66 Endocrinology PLAB 1/ UKMLA exam question. This is a common topic that has appeared in the past PLAB 1 exam.
A 25-year-old man originally from Zimbabwe, but currently residing in the UK, attends a clinic with complaints of persistent fatigue, cold intolerance, and unexplained weight gain over the past few months. On examination, you note dry skin, bradycardia, and mild non-pitting oedema. His recent blood investigations show a raised TSH level with a low free T4, consistent with primary hypothyroidism. Given his background and clinical presentation, which of the following is the most probable etiological factor for his condition?
A. Hashimoto's thyroiditis
B. Iodine deficiency
C. Thyroid adenoma
D. Toxic multinodular goitre
E. De Quervain's thyroiditis
The correct answer is: B. Iodine deficiency.
Explanation:
In the context of the clinical question, the primary clue is the patient's origin from Zimbabwe, a region where iodine deficiency is prevalent.
Iodine deficiency: is the predominant cause of hypothyroidism worldwide, particularly in areas where the soil and consequently the diet lack sufficient iodine. Such deficiencies are common in some parts of Africa, including Zimbabwe, and Asia. Therefore, despite him currently residing in the UK, his previous exposure in Zimbabwe makes this the most likely etiological factor.
Hashimoto's thyroiditis: is an autoimmune disorder and stands as the leading cause of hypothyroidism in iodine-sufficient regions like developed countries. It is characterized by the presence of anti-thyroid antibodies, lymphocytic infiltration of the thyroid gland, and gradual thyroid failure.
Thyroid adenoma: usually does not cause hypothyroidism. Most are non-functioning or 'cold' nodules, but some can be hyperfunctioning leading to hyperthyroidism.
Toxic multinodular goitre: typically results in hyperthyroidism, not hypothyroidism. It's characterized by multiple nodules in the thyroid gland producing excessive amounts of thyroid hormone.
De Quervain's thyroiditis: is a painful, subacute thyroiditis associated with viral infections. While it can initially cause transient hyperthyroidism due to the release of preformed thyroid hormones, it can subsequently lead to temporary hypothyroidism. However, the clinical presentation does not fit this case, as De Quervain’s usually presents with a painful thyroid gland.
It's crucial to recognize that a patient's background and origin can give essential hints regarding potential differential diagnoses, especially in conditions with regional variations like iodine deficiency-related hypothyroidism.
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Reference:
NICE guideline on thyroid disease: assessment and management. It covers investigating all suspected thyroid disease and managing primary thyroid disease (related to the thyroid rather than the pituitary gland). It does not cover managing thyroid cancer or thyroid disease in pregnancy. It states that iodine deficiency is the most common cause of hypothyroidism worldwide, but it is rare in the UK and other developed countries due to iodine supplementation in salt and other foods.
NICE clinical knowledge summary on hypothyroidism. It provides evidence-based or best clinical practice information regarding the diagnosis and subsequent management of hypothyroidism across community, ambulatory daycare and inpatient settings. It covers the causes, symptoms, investigations, treatment, monitoring, and referral of hypothyroidism. It mentions that iodine deficiency is a rare cause of hypothyroidism in the UK, but it may be seen in people who have migrated from areas of endemic iodine deficiency.
NICE evidence summary on the use of iodine supplements for pregnant and breastfeeding women. It reviews the evidence on the benefits and harms of iodine supplementation for pregnant and breastfeeding women in the UK, where iodine deficiency is mild to moderate. It concludes that there is insufficient evidence to support routine iodine supplementation for this population group, but it may be considered for women who are at high risk of iodine deficiency, such as those who follow a vegan diet or avoid dairy products.