Persistently elevated procalcitonin leading to the diagnosis of medullary thyroid carcinoma: a surgical case report

Medullary thyroid carcinoma (MTC) is typically diagnosed through elevated calcitonin levels, whereas procalcitonin (PCT) is mainly considered an infection marker. However, emerging evidence suggests that PCT may also have diagnostic value in MTC. We report the case of a 63-year-old man with recurrent biliary colic and persistently elevated PCT levels (up to 16.8 ng/ml) despite the absence of clinical or radiological signs of infection. This unexpected abnormality prompted further evaluation, leading to the incidental identification of a multinodular goiter with a suspicious thyroid nodule. Calcitonin was markedly elevated, and cytology was consistent with MTC (TIR 3B). The patient underwent total thyroidectomy with central lymphadenectomy, resulting in rapid normalization of both calcitonin and PCT postoperatively. This case highlights how unexplained PCT elevation in a non-endocrine clinical setting may provide an early clue to MTC. Persistent PCT elevation without infection should therefore prompt consideration of MTC, as combined assessment of calcitonin and PCT may improve diagnostic accuracy.