Recurrent Hyperparathyroidism Due to Hyperactive Ectopic Intrathymic Parathyroid Gland 20 Years After Parathyroidectomy.

Primary hyperparathyroidism is most commonly caused by a single adenoma, with multiglandular disease accounting for a smaller proportion of cases. A recurrent hyperparathyroidism decades after prior parathyroidectomy is uncommon and often presents with nonspecific multisystem symptoms that delay diagnosis. Ectopic parathyroid tissue, particularly in intrathymic or retrosternal locations, represents a challenging but important cause of persistent or recurrent disease. A 43‑year‑old woman with a history of three‑gland parathyroidectomy 20 years earlier presented with a year of progressive fatigue, generalized weakness, recurrent colicky abdominal pain, persistent nausea, and an 8‑kg unintentional weight loss. She also reported diffuse arthralgia, proximal myalgia, and significant neuropsychiatric symptoms, prompting psychiatric evaluation. Laboratory studies revealed hypercalcemia (10.9 mg/dl), markedly elevated parathyroid hormone (PTH) (1235 pg/ml), hypophosphatemia, vitamin D insufficiency, and hypomagnesemia. Imaging demonstrated destructive maxillofacial lesions, multiple sclerotic skeletal lesions, and persistent technetium‑99m sestamibi uptake in the mediastinum, consistent with an ectopic retrosternal parathyroid gland. The patient underwent thoracic surgical excision of the mass, with intraoperative PTH drop from 1235 pg/ml to 371 pg/ml. Histopathology confirmed an intrathymic parathyroid gland with hyperplasia and a dominant oxyphil pseudo‑adenomatous nodule. Following surgical excision, the patient experienced rapid biochemical normalization and complete resolution of her gastrointestinal, musculoskeletal, and neuropsychiatric symptoms. Serial outpatient follow‑up demonstrated the sustained normalization of calcium and PTH levels. This case highlights the importance of considering an ectopic intrathymic parathyroid tissue as a cause of late recurrent hyperparathyroidism, even decades after prior surgery. Persistent multisystem symptoms in patients with a history of parathyroidectomy warrant thorough biochemical evaluation and advanced imaging to ensure timely localization and definitive management.