Malignant thyroid neoplasm with ectopic Cushing's syndrome.

An adult man in his 30s with newly diagnosed diabetes mellitus and hypertension presented with a 33 lb weight gain, generalised swelling and classic Cushingoid features, including proximal muscle weakness, easy bruisability, wide violaceous striae and a painless, progressively enlarging right-sided neck swelling over the past month. Physical examination revealed a 4×4 cm thyroid mass, facial plethora and dorsocervical fat pads. Laboratory investigations confirmed hypercortisolism with elevated cortisol and Adrenocorticotropic Hormone(ACTH), with non-suppression on dexamethasone suppression tests. Imaging studies identified a malignant thyroid mass and bulky adrenal glands. Fine-needle aspiration cytology confirmed medullary thyroid carcinoma (MTC) with significantly elevated calcitonin and carcinoembryonic antigen. The patient was diagnosed with ectopic Cushing's syndrome secondary to MTC and underwent bilateral adrenalectomy followed by total thyroidectomy. Postoperatively, ACTH levels normalised; however, residual tumour was detected, necessitating external beam radiotherapy.