False positive results using calcitonin as a screening method for medullary thyroid carcinoma
A 32-year-old, female, white, Brazilian patient has sought medical advice with an endocrinologist as she noticed a lump in the cervical region. Thyroid palpation indicated an enlargement of the gland of about three to four times with irregularities in the lower left third and a palpable nodule in the lower right third. Ultrasound evidenced two nodules in the left lobe (0.6 × 0.9 and 1.0 × 1.0 cm), the lower third of the last one demonstrated hyperechoic and hypovascularized region. A solid nodule was also found next to the lower pole of the left lobe with no continuity to it, of 1cm the diameter. Normal levels of serum TSH and free T4, total and ionic serum calcium, inorganic phosphorus and chlorine were showed, and anti-thyroglobulin and anti-thyroperoxidase antibodies were reactants.\nCalcitonemia was 10 pg/mL (normal levels=<2 pg/mL). Thyroid nodule fine needle aspiration was done under direct visualization with ultrasound, and anatomopathologic examination disclosed a follicular pattern. The immunohistochemical staining of the aspirated material was negative for calcitonin, diffusely positive for thyroglobulin, negative for chromogranin and carcinoembryonic antigen, positive for AC1 and AC3, negative for galectin-1, negative for HBME-1, and positive for TTF-1. Stimulation test for calcitonin was performed and response to the test was positive, reaching a maximum of 79 pg/mL 2 minutes after calcium infusion []. The patient underwent a thyroidectomy due to the follicular lesion. The congealing examination evidenced chronic lymphocytic thyroiditis in the nodules. Immunohistochemical staining was positive for calcitonin in the inflammatory and in the C cells with no evidence of C cells hyperplasia. Post-operative hypothyroidism was appropriately treated with levothyroxine. Serum levels of thyroglobulin and calcitonin levels were undetectable in the post-operative evaluation.