title: Hyperthyroidism due to an intrathoracic tumour in a dog with test results suggesting hyperadrenocorticism.
abstract: The elevated urinary corticoid/creatinine ratios of an 11-year-old Jack Russell terrier with polyuria were suppressible in a high-dose dexamethasone suppression test, which was suggestive of pituitary-dependent hyperadrenocorticism. The absence of physical and routine-laboratory changes compatible with hyperadrenocorticism and the relatively high plasma thyroxine concentration were the impetus for additional studies of thyroid and adrenocortical functions. A high plasma thyroxine concentration (62 nmol/l; 5.0 microg/100 ml) suggested the presence of hyperthyroidism. Radiography, (99m)TcO(4) (-) scintigraphy, ultrasonography, computed tomography and cytology revealed a hyperfunctioning intrathoracic thyroid tumour. In the low-dose dexamethasone suppression test, the plasma cortisol concentration exceeded the reference value of 40 nmol/l (1.4 microg/100 ml) at eight hours after dexamethasone administration (0.01 mg/kg intravenously), a test result compatible with hyperadrenocorticism. In conclusion, this report represents the first case of a dog with an autonomously hyperfunctioning thyroid tumour in the thorax. The elevated urinary corticoid excretion and the positive low-dose dexamethasone suppression test may be explained by alterations in cortisol metabolism, the stress of the hyperthyroid state or both.
authors.affiliation: Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
authors.forename: Q E M
authors.initials: QE
authors.lastname: Stassen
authors.forename: G
authors.initials: G
authors.lastname: Voorhout
authors.forename: E
authors.initials: E
authors.lastname: Teske
authors.forename: A
authors.initials: A
authors.lastname: Rijnberk
mesh_terms: D000308:Adrenocortical Hyperfunction / Q000097:blood / Q000175:diagnosis / Q000662:veterinary; D000818:Animals; D003907:Dexamethasone; D003937:Diagnosis, Differential; D004283:Dog Diseases / Q000097:blood / Q000175:diagnosis*; D004285:Dogs; D017809:Fatal Outcome; D006980:Hyperthyroidism / Q000097:blood / Q000209:etiology / Q000662:veterinary*; D008297:Male; D013963:Thyroid Hormones / Q000097:blood; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis / Q000662:veterinary*
chemical_list: D013963:Thyroid Hormones; D003907:Dexamethasone