Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the most common cause of hypothyroidism in developed countries?

1. Iodine deficiency

2. Autoimmune disorders

3. Thyroiditis

4. Surgical removal of the thyroid

The correct answer is: Autoimmune disorders

In developed countries, the most common cause of hypothyroidism is indeed autoimmune disorders, with Hashimoto's thyroiditis being the most prevalent form. This condition occurs when the body's immune system mistakenly targets and damages the thyroid gland, leading to inadequate production of thyroid hormones. Hashimoto's thyroiditis is characterized by inflammation of the thyroid, and over time, this inflammation can significantly impair the gland's ability to synthesize thyroid hormones, resulting in hypothyroidism. In areas where iodine levels are sufficient, autoimmune causes have overtaken iodine deficiency, which is more common in developing regions. Other potential causes, like thyroiditis and surgical removal of the thyroid, do occur but are not as prevalent as autoimmune disorders. Thyroiditis can refer to several types of inflammation that might affect the thyroid, and surgical removal is typically a consequence of existing thyroid disease rather than a common cause of hypothyroidism in the general population. Iodine deficiency has dramatically decreased in developed countries due to the widespread use of iodized salt and a balanced diet, making autoimmune disorders the leading cause of hypothyroidism instead.