Ectopic parathyroid carcinoma coexisting with Graves' disease: A case report and literature review

Parathyroid carcinoma (PC) is a rare malignancy typically characterized by severe hypercalcemia and markedly elevated parathyroid hormone (PTH). The coexistence of PC with Graves' disease (GD) is exceptionally rare and presents a critical diagnostic challenge. The symptoms of hyperthyroidism can mask the clinical features of parathyroid disease, and when PC presents with only mild biochemical abnormalities - as in this case - the risk of misdiagnosis or delayed treatment is significantly increased. This case is reported to highlight the deceptive nature of this combination and the necessity for vigilance even when laboratory values are not drastically elevated.

A 56-year-old patient presented with clinical manifestations of hyperthyroidism and a palpable left-sided neck mass. Crucially, the patient lacked the classic red flags of PC, such as severe bone pain, renal colic, or hypercalcemic crisis, which typically prompt immediate investigation for malignancy.

Initial laboratory evaluations revealed hyperthyroidism consistent with Graves' disease. However, calcium and parathyroid hormone (PTH) levels were only mildly elevated, contrasting with the markedly high levels typically seen in carcinoma. A computed tomography scan identified a substantial mass located between the left carotid sheath and the thyroid gland, suggesting an ectopic lesion. Post-surgical pathological examination definitively confirmed the diagnosis of PC.

Given the presence of the neck mass and biochemical abnormalities, the patient underwent surgical resection of the tumor.

The surgery was successful with no immediate complications. Postoperatively, the serum calcium and PTH levels returned to normal ranges rapidly. The patient recovered without complications, and follow-up has shown no signs of recurrence.

This case highlights the diagnostic challenge of PC when masked by Graves' disease and presenting with atypical, mild biochemical elevations. Clinicians should maintain a high index of suspicion for parathyroid malignancy in patients with Graves' disease who present with a neck mass, even if calcium and PTH levels do not reach the extreme thresholds typically associated with carcinoma. Early identification and radical resection are crucial for favorable prognosis.