A patient with initial hyperthyroidism that progresses to hypothyroidism is indicative of which condition?

The scenario described, where a patient initially presents with hyperthyroidism that later progresses to hypothyroidism, is most indicative of Hashimoto's thyroiditis. This condition is an autoimmune disorder in which the immune system attacks the thyroid gland, leading to its destruction and impairment of hormone production. Initially, the inflammation from the autoimmune attack can cause leakage of thyroid hormones into the bloodstream, resulting in transient hyperthyroidism. As the disease progresses and thyroid tissue is destroyed, the patient eventually develops hypothyroidism due to decreased hormone production.

In contrast, Graves' disease is characterized by sustained hyperthyroidism due to excessive production of thyroid hormones, typically not leading to a subsequent hypothyroid state. Subacute thyroiditis may present with hyperthyroid symptoms due to thyroiditis but generally resolves with recovery of normal thyroid function, rather than progressing to hypothyroidism. Pernicious anemia is unrelated to thyroid function and involves a deficiency in vitamin B12 due to intrinsic factor deficiency, not thyroid hormone levels. Thus, Hashimoto's thyroiditis is the condition that aligns with the pattern of hyperthyroidism followed by hypothyroidism.