Primary hyperparathyroidism due to ectopic parathyroid adenoma with bone lesions mimicking skeletal neoplasm: a case...

Parathyroid adenoma accounts for the majority of primary hyperparathyroidism (PHPT) cases. However, ectopic presentations-particularly those arising outside the typical cervical anatomical landmarks-remain rare and diagnostically challenging. These lesions often mimic skeletal pathologies, thereby increasing the risk of misdiagnosis.

We report the case of a 60-year-old male tile-layer who was admitted with a 10-month history of progressive left-sided rib pain. The medical history of the patient was notable for multiple fractures and chronic low back pain. On physical examination, localized swelling was observed over the left ninth rib. Biochemistry serum tests revealed hypercalcemia (serum calcium: 3.07 mmol/L), hypophosphatemia (serum phosphate: 0.62 mmol/L), and elevated alkaline phosphatase. Computed tomography demonstrated expansile lytic lesions involving multiple ribs and scapulae, initially suggestive of a primary bone tumor. The patient underwent resection of the left ninth rib lesion, and histopathology evaluation revealed a brown tumor. Subsequent endocrine function and organs evaluation identified markedly elevated parathyroid hormone (PTH) levels (peak: 1,912.1 pg/mL). Cervical medical imaging procedures and intraoperative exploration localized an ectopic mass situated medial to the left sternocleidomastoid muscle. The lesion was completely excised, and histopathology confirmed an ectopic parathyroid adenoma with focal hyperplasia. Postoperatively, the patient showed a rapid decrease in PTH levels, followed by transient hypocalcemia and secondary reactive hyperparathyroidism.

This case highlights a rare instance of an intrasterneomastoid ectopic parathyroid adenoma misdiagnosed as a skeletal neoplasm. The unusual anatomical location contributed to diagnostic delay and initial mismanagement. Timely surgical excision led to normalization of biochemical markers. Our findings underscore the importance of considering endocrine disorders-particularly ectopic parathyroid pathology-in patients presenting with unexplained multiple osteolytic lesions, to avoid misdiagnosis and ensure appropriate treatment.