Severe hyperprolactinemia secondary to primary hypothyroidism with normal pituitary imaging

Hyperprolactinemia is often attributed to pituitary adenomas; however, primary hypothyroidism is an important and often overlooked secondary cause. We report the case of a 36-year-old woman who presented with giddiness, fatigue, menstrual irregularity, and markedly elevated serum prolactin levels 339 ng/mL (SI: 339 µg/L); reference range, 5-25 ng/mL (SI: 5-25 µg/L) with normal pituitary imaging. Biochemical evaluation revealed severe primary hypothyroidism with significantly elevated thyroid-stimulating hormone levels. Treatment with levothyroxine alone resulted in clinical and biochemical improvement, confirming the diagnosis of hypothyroidism-induced hyperprolactinemia. This case highlights the importance of evaluating thyroid function in patients with hyperprolactinemia to avoid misdiagnosis and unnecessary treatment.