What causes hyperthyroidism in the thyrotoxic phase of postpartum thyroiditis?

The hyperthyroidism observed in the thyrotoxic phase of postpartum thyroiditis is primarily caused by the release of stored thyroid hormones. In postpartum thyroiditis, there is an initial inflammatory response in the thyroid gland, often leading to the destruction of thyroid follicles. This destruction causes the pre-formed thyroid hormones (thyroxine [T4] and triiodothyronine [T3]) that were stored in the gland to be released into the circulation, resulting in elevated levels of these hormones in the blood.

During this thyrotoxic phase, the body does not produce new thyroid hormones; rather, it is the existing hormones that were stored and subsequently released due to the inflammatory process. This mechanism is distinct from other causes of hyperthyroidism, where excess hormone production occurs.

The other options are not applicable in the context of postpartum thyroiditis. The synthesis of new thyroid hormones is not the mechanism at play here, as the gland is generally not functioning optimally during this phase. Increased iodine intake and medication-induced thyroiditis may contribute to hyperthyroidism in different contexts but do not directly relate to the pathophysiology of postpartum thyroiditis. Thus, the key process leading to the hyperthyroid state in this condition is the release