Clinical and biochemical alterations associated with excess calcitonin in a dog with medullary thyroid carcinoma

We present a 10-year-old mongrel dog with progressive weight loss, polyuria and polydipsia. Physical examination revealed poor body condition, systemic hypertension (on average 165 mmHg) and a cervical mass that was confirmed by ultrasound in the right thyroid lobe (diameter 4.0 cm). Blood biochemistry on two different days revealed a low ionised calcium concentration (1.1 and 0.81 mmol/L; reference range: 1.1-1.3 mmol/L) associated with an elevated plasma calcitonin concentration in the same sample (44.8 and 49 pg/mL; reference range: <2 pg/mL). A low urine specific gravity (1.012) was also found. Total thyroxine concentration was low, corresponding to euthyroid sick syndrome. Hypercalcitoninemia, hypocalcaemia and clinical signs resolved after an uncomplicated right thyroidectomy. Positive staining of the neoplasm for calcitonin on immunohistochemistry confirmed a medullary thyroid carcinoma. This is the first report describing the clinical signs and biochemical alterations associated with excess calcitonin in a dog with medullary thyroid carcinoma confirmed by immunohistochemistry.