30 A 55-year-old man has a palpable right thyroid mass discovered after his sister was diagnosed with medullary thyroid carcinoma. He denied hoarseness or symptoms of hypothyroidism or hyperthyroidism. He reported a history of medically controlled hypertension with occasional flushing spells. In addition to his sister with medullary thyroid carcinoma, his paternal uncle died of thyroid cancer of unknown origin. The physical examination revealed a 2-cm right thyroid nodule without palpable lymphadenopathy. Vocal cord function is normal. The patient has a thyroid nodule with a family history of medullary thyroid cancer and is at high risk for familial medullary thyroid carcinoma, multiple endocrine neoplasia (MEN) IIa, or MEN-IIb. Genetic testing of the patient’s sister and of the patient if the sister is positive or unavailable for testing is diagnostic and required for this autosomal dominant hereditary disease. If this patient is positive, all of his siblings and offspring require testing and therapeutic or prophylactic thyroidectomy if positive. MEN-IIa is associated with hyperparathyroidism and pheochromocytoma; MEN-IIb is associated with pheochromocytoma, mucosal neuromas, and pancreatic islet cell tumors. Biochemical screening for these associated disorders is important preoperatively to identify hyperparathyroidism, which should be addressed concomitantly at the time of thyroidectomy. Screening for pheochromocytoma is necessary preoperatively so that it can be treated before thyroidectomy is performed to minimize the risk of perioperative hypertensive crisis. The workup of a thyroid nodule is reviewed in the previous chapter and includes screening thyroid stimulating hormone (TSH) ultrasound, and ultrasound-guided fine-needle biopsy, all of which are indicated and should be performed. The cytology specimen should be sent for immunohistochemical staining for calcitonin in addition to traditional hematoxylin and eosin staining. Specific to this case is the family history of medullary thyroid carcinoma, which impacts the medical management of this patient. Calcitonin is produced by parafollicular c-cells within the thyroid, as well as their malignant counterpart medullary thyroid carcinoma. Serum calcitonin is a reasonable screening test in all patients with thyroid nodules because it has greater sensitivity than fine-needle biopsy for the diagnosis of medullary carcinoma. In patients with a family history, it is mandatory. Slight elevation of serum calcitonin may be normal or may represent c-cell hyperplasia, a precursor to medullary carcinoma in hereditary patients. Larger elevations above 40 or 100 are more specific for medullary cancer. Genetic testing for the Ret
Medullary Thyroid Carcinoma
History
Differential Diagnosis—Key Points
Diagnostic Tests
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