Synchronous Multiple Parathyroid Carcinoma: A Challenging Diagnosis Influencing Optimal Primary Treatment-A Literature Review to Guide Clinical Decision-Making.

Synchronous multiple parathyroid carcinoma is a rare condition within the already uncommon landscape of parathyroid malignancies, which comprise less than 1% of sporadic primary hyperparathyroidism cases. To date, only seven cases of synchronous multiple parathyroid carcinoma in sporadic primary hyperparathyroidism have been documented. This exceptional rarity complicates both the diagnostic process and therapeutic decision-making. Clinically, parathyroid carcinoma typically presents as a single mass determining severe symptoms. However, no single clinical, biochemical, or imaging feature allows for definitive preoperative diagnosis. Imaging modalities such as ultrasound and sestamibi scans exhibit variable sensitivity and may overlook multi-gland involvement. Histopathological examination remains the only reliable diagnostic method. Management strategies are also controversial: while some advocate for conservative surgery, en bloc resection is generally recommended for its association with improved local control and disease-free survival. Given the exceptional occurrence of synchronous multiple parathyroid carcinoma, there is a lack of standardized protocols for managing parathyroid carcinoma in cases of synchronous and multiple gland involvement. Early multidisciplinary evaluation and individualized treatment planning are therefore crucial. This review aims to synthesize the presently available knowledge about synchronous multiple parathyroid carcinoma, assist clinicians with the limited data available, and discuss the main challenges in the management of this rare entity.