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Prevalence and degree of thyroid pathology in hyperthyroid cats increases with disease duration: a cross-sectional analysis of 2096 cats referred for radioiodine therapy

Objectives Hyperthyroidism is common in cats, but there are no reports that evaluate its severity or underlying thyroid tumor disease based on disease duration (ie, time from original diagnosis). The objective of this study was to compare serum thyroxine (T4) concentrations and thyroid scintigraphic...

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Bibliographic Details
Published in:Journal of feline medicine and surgery 2016-02, Vol.18 (2), p.92-103
Main Authors: Peterson, Mark E, Broome, Michael R, Rishniw, Mark
Format: Article
Language:English
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Summary:Objectives Hyperthyroidism is common in cats, but there are no reports that evaluate its severity or underlying thyroid tumor disease based on disease duration (ie, time from original diagnosis). The objective of this study was to compare serum thyroxine (T4) concentrations and thyroid scintigraphic characteristics of cats referred for radioiodine treatment based on disease duration. Methods This was a cross-sectional study of 2096 cats with hyperthyroidism. Cats were divided into five groups based on time from diagnosis: ⩽1 year (n = 1773); >1–2 years (n = 169); >2–3 years (n = 88); >3–4 years (n = 35); and >4–6.1 years (n = 31). Methimazole, administered to 996 (47.5%) cats, was stopped at least 1 week prior to examination to allow for serum T4 testing. Each thyroid scintiscan was evaluated for pattern (unilateral, bilateral, multifocal), location (cervical, thoracic inlet, chest) and size (small, medium, large, huge) of the thyroid tumor, as well as features suggesting malignancy. Results Median serum T4 concentration increased with increasing disease duration from 100 nmol/l (⩽1 year) to 315 nmol/l (>4–6.1 years) (P 8 cm3) thyroid tumors increased from 5.1% (⩽1 year) to 88.6% (>4–6.1 years), while the prevalence of intrathoracic tumor tissue increased from 3.4% (⩽1 year) to 32.3% (>4–6.1 years). Prevalence of suspected thyroid carcinoma (characterized by severe hyperthyroidism; huge, intrathoracic, multifocal tumors; refractory to methimazole treatment) increased with increasing disease duration from 0.4% (⩽1 year) to 19.3% (>4–6.1 years). Conclusions and relevance Our results indicate that the prevalence of severe hyperthyroidism, large thyroid tumors, multifocal disease, intrathoracic thyroid masses and suspected malignant disease all increase with disease duration in cats referred for radioiodine therapy.
ISSN:1098-612X
1532-2750
1532-2750
DOI:10.1177/1098612X15572416