Review Question - QID 100370

The patient in this question displays many of the common clinical findings of hypothyroidism, which is most commonly caused by primary hypothyroidism. The most sensitive test for diagnosis is an elevated serum TSH.

The normal hypothalamic-pituitary-thyroid axis consists of TRH from the hypothalamus stimulating the release of TSH from the pituitary. Released TSH then acts on the thyroid, leading to thyroid hormone release. In primary hypothyroidism, TSH levels are elevated because there is an absence of appropriate feedback inhibition on the hypothalamus from thyroid hormones (T3 and T4).

Hueston reviews the treatment of hypothyroidism. He emphasizes the importance of primary care physicians' ability to diagnose and treat hypothyroidism as it is incredibly common in the US population, second only to diabetes mellitus in prevalence. The incidence increases with advancing age, affecting 2-3% of older women.

Chakera et al. explain that the most common cause of primary hypothyroidism is autoimmune thyroiditis. However, iodine deficiency remains an important cause worldwide. The authors note that levothyroxine is a common treatment for hypothyroidism and highlight the drug's long 7 day half-life.

Illustration A depicts the hypothalamic-pituitary-thyroid axis and demonstrates the stimulation and feedback mechanisms of involved hormones.

Incorrect Answers:
Answer 1: Elevated thyroid hormones would be consistent with hyperthyroidism.
Answer 2: Though decreased thyroid hormone is consistent with hypothyroidism, serum TSH levels are a better indication of primary hypothyroidism.
Answer 4: Though hypercholesterolemia is a clinical finding sometimes seen with hypothyroidism, high serum TSH is the more specific diagnostic tool.
Answer 5: Low TSH would be more consistent with hyperthyroidism.