Thyrotoxicosis With Medullary Thyroid Carcinoma: A Rare Endocrine Diagnostic Challenge.

The incidence of a hyper-functioning thyroid gland presenting alongside an underlying malignancy rarely occurs. Herein, we present a rare case of a 56-year-old female patient presenting with features of hyperthyroidism only to be later diagnosed with an underlying malignancy, medullary thyroid carcinoma (MTC). Ultrasonography (USG) of the neck revealed a suspicious nodule with microcalcifications in the right lobe of the thyroid. Subsequent CT imaging of the neck indicated possible cervical and mediastinal lymph node involvement. Fine-needle aspiration cytology (FNAC) confirmed the presence of high-grade thyroid carcinoma. The patient underwent total thyroidectomy with neck node dissection after which her symptoms subsided. She was well at her last follow-up.