Medullary Thyroid Carcinoma Masquerading as Tuberculosis Reactivation: A Case of Diagnostic Concealment in an Occult Thyroid Nodule.

Medullary thyroid carcinoma (MTC) with tumour-associated granulomas presents a significant diagnostic challenge in tuberculosis (TB)-endemic regions, particularly when thyroid nodules are non-palpable. We report a 75-year-old woman with treated pulmonary TB who presented with dyspnoea and pleural effusion, leading to initial clinical suspicion of TB reactivation. An incidental non-palpable thyroid nodule discovered on ultrasound was revealed to be MTC with epithelioid granulomas on fine-needle aspiration cytology. The absence of a palpable neck mass diverted clinical attention towards pulmonary TB, demonstrating how thyroid malignancy can remain concealed by TB manifestations. Elevated serum calcitonin (620 pg/mL) and Congo red-positive amyloid deposits confirmed MTC post-thyroidectomy. This case underscores the critical importance of systematic calcitonin testing in granulomatous thyroid lesions, even in non-palpable nodules, to prevent delayed cancer diagnosis in TB-prevalent healthcare settings.