False positive results using calcitonin as a screening method for medullary thyroid carcinoma
A 59-year-old, male, Egyptian patient, started treatment for obesity with an endocrinologist, taking sibutramine and orlistat. After clinical examination a thyroid ultrasound was performed and evidenced hypoechogenic solid nodule of 1.2 cm the diameter in the upper third of the right lobe and an adjacent cyst with parietal calcifications of 0.6 cm. He had normal TSH and free T4, with negative anti-thyroperoxidase and anti-thyroglobulin antibodies. Serum basal calcitonin levels of 19 pg/mL were detected (normal levels=<2 pg/mL). Stimulation test for calcitonin was performed reaching a rate of up to 890 pg/mL, observed at two minutes after calcium infusion []. Total thyroidectomy was performed. During surgery four nodules were identified in the right lobe and two nodules in the left lobe. In the anatomopathologic examination 12 nodules were observed, evidencing adenomatous goiter, except one white, calcified and encapsulated 0.3 cm nodule classified as a classic variable papillary microcarcinoma. Among the nodules, in both lobes, diffuse hyperplasia of C cells was observed [], however with no presence of atypia. Immunohistochemistry was positive for chromogranin and calcitonin in numerous interstitial and intrafollicular cells []. Three months after surgery, measurement of thyroglobulin and calcitonin levels was performed, after two injections of recombined TSH, and rates for both of them were undetectable what remain for five years [].