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Abstract

Objective—To determine the usefulness of measuring serum free thyroxine (T4) concentration as a diagnostic test for hyperthyroidism in cats, and to determine the influence of nonthyroidal disease on free T4 concentration in cats without hyperthyroidism.

Design—Prospective case series.

Animals—917 cats with untreated hyperthyroidism, 221 cats with nonthyroidal disease, and 172 clinically normal cats.

Procedure—Serum free T4, total T4, and total triiodothyronine (T3) concentrations were measured in cats with untreated hyperthyroidism and cats with nonthyroidal disease. Serum total T4 and T3 concentrations were determined by use of radioimmunoassay, and free T4 concentration was measured by use of direct equilibrium dialysis. Reference ranges for hormone concentrations were established on the basis of results from the 172 clinically normal cats.

Results—Sensitivity of serum free T4 concentration as a diagnostic test for hyperthyroidism was significantly higher than the test sensitivity of either total T4 or T3 concentration. Of the 221 cats with nonthyroidal disease, 14 had a high free T4 concentration (ie, falsepositive result). Therefore, calculated specificity of measuring serum free T4 concentration as a diagnostic test for hyperthyroidism was significantly lower than test specificity of measuring either the total T4 or T3 concentration.

Conclusions and Clinical Relevance—Results indicate that determination of free T4 concentration is useful in the diagnosis of hyperthyroidism, especially in cats in which hyperthyroidism is suspected but total T4 and T3 concentrations are within reference ranges. However, because some cats with nonthyroidal disease have high serum free T4 concentrations, hyperthyroidism should not be diagnosed solely on the finding of high free T4 concentration. (J Am Vet Med Assoc 2001;218:529–536)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To identify the most common sites of and possible predisposing factors for nonunions in cats with fractures of the appendicular skeleton.

Design—Retrospective study.

Animals—344 cats treated for fractures between 1998 and 2002, 18 of which developed nonunions.

Procedures—Information collected from the medical records included signalment; type of trauma; fracture location, orientation, and type; degrees of displacement and comminution; treatment; and outcome.

Results—The tibia and proximal portion of the ulna were identified as the most common sites for nonunions. Factors significantly associated with development of a nonunion included age, body weight, affected bone, fracture type, degree of comminution, and fixation type, with older cats, heavier cats, cats with fractures of the tibia or proximal portion of the ulna, cats with open fractures, cats with comminuted fractures, and cats with fractures stabilized with a type II external skeletal fixator being significantly more likely to develop a nonunion. Eleven of the 18 cats with nonunions had a successful outcome following treatment of the nonunion.

Conclusions and Clinical Relevance—Results suggest that in cats, fractures involving the tibia and proximal portion of the ulna are more likely to develop nonunions than are fractures involving other sites but that many factors may increase the risk of nonunion. Use of excessively large and rigid type II external skeletal fixators may be associated with development of nonunions; however, type II external skeletal fixators were commonly used to stabilize fractures in sites predisposed to nonunion. (J Am Vet Med Assoc 2005;226:77–82)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To identify within guanosine triphosphate–binding proteins (G proteins) the subset of inhibitory G proteins (Gi) that have decreased expression in adenomatous thyroid glands obtained from hyperthyroid cats.

Sample Population—Adenomatous thyroid glands obtained from 5 hyperthyroid cats and normal thyroid glands obtained from 3 age-matched euthyroid cats.

Procedure—Expression of Gi1, Gi2, and Gi3 in enriched membrane preparations from thyroid glands was quantified by use of immunoblotting with Gi subtype-specific antibodies.

Results—Expression of Gi2 was significantly decreased in tissues of hyperthyroid glands, compared with expression in normal thyroid tissue. Expression of Gi1 and Gi3 was not significantly different between normal thyroid tissues and tissues from hyperthyroid glands.

Conclusions and Clinical Relevance—A decrease in Gi2 expression decreases inhibition of adenylyl cyclase and allows a relative increase in stimulatory G protein expression. This results in increased amounts of cAMP and subsequent unregulated mitogenesis and hormone production in hyperthyroid cells. Decreased Gi2 expression may explain excessive growth and function of the thyroid gland in cats with hyperthyroidism. (Am J Vet Res 2005;66:1478–1482)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether nonthyroidal disease of various causes and severity is associated with abnormalities in baseline serum concentrations of total thyroxine (T4), triiodothyronine (T3), free T4, or thyrotropin (thyroid-stimulating hormone [TSH]) in dogs believed to be euthyroid.

Design—Case-control study.

Animals—223 dogs with confirmed nonthyroidal diseases and presumptive normal thyroid function, and 150 clinically normal dogs.

Procedure—Serum total T4, total T3, free T4, and TSH concentrations were measured in dogs with confirmed nonthyroidal disease. Reference ranges for hormone concentrations were established on the basis of results from 150 clinically normal dogs.

Results—In dogs with nonthyroidal disease, median serum concentrations of total T4, total T3, and free T4 were significantly lower than those in clinically normal dogs. Median serum TSH concentration in sick dogs was significantly greater than that of clinically normal dogs. When stratified by severity of disease (ie, mild, moderate, and severe), dogs with severe disease had low serum concentrations of total T4, total T3, or free T4 more commonly than did dogs with mild disease. In contrast, serum TSH concentrations were more likely to remain within the reference range regardless of severity of disease.

Conclusions and Clinical Relevance—Results indicate that serum total T4, free T4, and total T3 concentrations may be low (ie, in the hypothyroid range) in dogs with moderate to severe nonthyroidal disease. Serum TSH concentrations are more likely to remain within the reference range in sick dogs. (J Am Vet Med Assoc 2001;219:765–769)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine testing protocols used by board-certified internists and dermatologists for diagnosis of hyperadrenocorticism (HAC) in dogs.

Design—Survey.

Study Population—Board-certified internists and dermatologists.

Procedure—A questionnaire was mailed to 501 specialists to gather information pertaining to diagnosis of HAC.

Results—206 surveys were returned. Only 26% of respondents indicated they would screen a dog for HAC if the dog had only a few laboratory abnormalities consistent with HAC and no clinical signs consistent with the disease; 31% indicated they would not, and 43% indicated they would sometimes. Overall, 55% of respondents indicated they preferred to use the lowdose dexamethasone suppression test for routine screening of dogs suspected to have HAC. However, many respondents indicated they would use a different screening test than usual in particular circumstances. Sixty-eight percent of respondents indicated they would perform a second screening test for confirmation if results of an initial screening test were positive but there were few clinical or laboratory abnormalities consistent with HAC. Most respondents used some sort of test to differentiate pituitary-dependent HAC from HAC secondary to an adrenal tumor (AT), but no 1 test was clearly preferred. Ultrasonography was commonly used, whereas computed tomography and magnetic resonance imaging were not, even if available.

Conclusions and Clinical Relevance—Results suggest that the low-dose dexamethasone suppression test is the test most commonly used to screen dogs for HAC but that other tests may be used in certain circumstances. A variety of tests were used to differentiate pituitary-dependent HAC from HAC secondary to an AT. (J Am Vet Med Assoc 2002;220:1643–1649)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To describe findings in dogs with exogenous thyrotoxicosis attributable to consumption of commercially available dog foods or treats containing high concentrations of thyroid hormone.

Design—Retrospective and prospective case series.

Animals—14 dogs.

Procedures—Medical records were retrospectively searched to identify dogs with exogenous thyrotoxicosis attributable to dietary intake. One case was found, and subsequent cases were identified prospectively. Serum thyroid hormone concentrations were evaluated before and after feeding meat-based products suspected to contain excessive thyroid hormone was discontinued. Scintigraphy was performed to evaluate thyroid tissue in 13 of 14 dogs before and 1 of 13 dogs after discontinuation of suspect foods or treats. Seven samples of 5 commercially available products fed to 6 affected dogs were analyzed for thyroxine concentration; results were subjectively compared with findings for 10 other commercial foods and 6 beef muscle or liver samples.

Results—Total serum thyroxine concentrations were high (median, 8.8 μg/dL; range, 4.65 to 17.4 μg/dL) in all dogs at initial evaluation; scintigraphy revealed subjectively decreased thyroid gland radionuclide in 13 of 13 dogs examined. At ≥ 4 weeks after feeding of suspect food or treats was discontinued, total thyroxine concentrations were within the reference range for all dogs and signs associated with thyrotoxicosis, if present, had resolved. Analysis of tested food or treat samples revealed a median thyroxine concentration for suspect products of 1.52 μg of thyroxine/g, whereas that of unrelated commercial foods was 0.38 μg of thyroxine/g.

Conclusions and Clinical Relevance—Results indicated that thyrotoxicosis can occur secondary to consumption of meat-based products presumably contaminated by thyroid tissue, and can be reversed by identification and elimination of suspect products from the diet.

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To evaluate pituitary-adrenal function in a population of critically ill dogs by measuring serial plasma concentrations of basal cortisol, ACTH-stimulated cortisol, and endogenous ACTH.

Design—Prospective study.

Animals—20 critically ill dogs admitted to an intensive care unit (ICU).

Procedure—Basal plasma cortisol, ACTH-stimulated cortisol, and endogenous ACTH concentrations were measured for each dog within 24 hours of admission and daily until death, euthanasia, or discharge from the ICU. Established reference ranges for healthy dogs were used for comparison. Survival prediction index (SPI) scores were calculated for each dog within 24 hours of admission.

Results—No significant difference was found between initial concentrations of basal cortisol, ACTH-stimulated cortisol, and endogenous ACTH in 13 dogs that survived and those in 7 dogs that died. High initial basal endogenous ACTH concentrations were correlated with subsequent high values. Low basal ACTH-stimulated cortisol concentrations were predictive of higher subsequent values. All basal and ACTH-stimulated cortisol concentrations were within or above the reference range in the 52 plasma samples collected from the 20 dogs during hospitalization. The SPI scores correlated with outcome (ie, alive or dead), but none of the plasma hormone concentrations correlated with SPI score or outcome.

Conclusions and Clinical Relevance—Results indicate that none of the critically ill dogs in our study population developed adrenal insufficiency during hospitalization in the ICU. (J Am Vet Med Assoc 2002;220:615–619)

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in Journal of the American Veterinary Medical Association