Pitfalls in calcitonin measurement: case report
Ioana Vasiliu1, Delia Ciobanu2, Didona Ungureanu3, Roxana Balcan1, Safae ElMekkaoui1, Jeanina Idriceanu1, Voichita Mogos1 & Carmen Vulpoi1
Calcitonin (CT) is a sensitive marker for medullary thyroid carcinoma, but its routine measurement in patients with thyroid nodules is a controversial issue. Generally, an elevated serum calcitonin strongly suggests the presence of medullary thyroid carcinoma (MTC); however high CT levels may be found in other thyroid or non-thyroidal conditions. We report the case of a 49-year-old woman who consulted at the ambulatory of endocrinology for recent thyroid soreness. Biological findings revealed inhibited TSH (0.1 mUI/l) and elevated CT (128.4 pg/ml, n<11 pg/ml), and she was refered to the Endocrinological Departament. Clinical examination found asymmetrical enlargement of the thyroid gland, subfebrility (37.3 °C), tachycardia (100/min), tremor. Thyroid ultrasound revealed inhomogeneous, hypo echoic pattern with the presence of two adjacent nodules in the right lob: of 0.9 and 2.4 cm with intense internal Doppler signal. She had minor sensitivity at thyroid palpation, but when FNAB was performed she complained of intensive pain. Low TSH with high fT4 values (3.8 ng/ml, n 0.82) confirmed thyrotoxicosis. Positive antithyroid antibodies (ATPO=102 UI/ml n<40, ATg=15.3UI/ml n<4) suggested an autoimmune disorder, but high ESR (77 mm/h), clinical and ultrasound data and cytology (multinuclear giant cells) diagnosed a subacute thyroiditis (SAT), whitch had a spectacular improvement after corticotherapy (ESR=8 mm/h, CT=4.1 pg/ml). Measurement of calcitonin is a highly sensitive method for the detection of MTC, but has a low specificity. Several physiological and pathological thyroid conditions other than medullary thyroid carcinoma have been associated with increased calcitonin levels (follicular and papillary carcinoma, chronic autoimmune thyroiditis). Patients with chronic lymphocytic thyroiditis present C-cell hyperplasia that may lead to increased calcitonin levels. We believe that during the inflammatory process (existed in SAT) not only follicular, but also parafollicular (C) cells may be destroyed, leading to high CT levels. Normalization of CT after remission of SAT sustains this supposition.