Objective: To evaluate clinical and laboratory findings in 225 dogs with naturally occurring hypoadrenocorticism diagnosed over a 14-year period. Design: Retrospective case series. Animals: 220 dogs with primary hypoadrenocorticism and 5 dogs with secondary hypoadrenocorticism (primary ACTH deficiency). Procedure: We reviewed medical records of all dogs with naturally occurring hypoadrenocorticism examined at The Animal Medical Center between 1979 and 1993 or at Tufts University, Foster Hospital for Small Animals, between 1987 and 1993. Results: Dogs ranged from 4 months to 14 years old. Most (71%) were female, and female dogs had a significantly higher relative risk of developing hypoadrenocorticism than did males. Great Danes, Portuguese Water Dogs, Rottweilers, Standard Poodles, West Highland White Terriers, and Wheaton Terriers had a significantly higher relative risk of developing hypoadrenocorticism than did dogs of other breeds. Common owner complaints included lethargy, poor appetite, and vomiting, whereas lethargy, weakness, and dehydration were common abnormalities detected on physical examination. Serum biochemical testing at the time of diagnosis revealed moderate-to-severe azotemia and hyperphosphatemia in most dogs. In 99 of 172 (57.6%) dogs that had a pretreatment urinalysis performed, urine specific gravity was < 1.030 even though dogs were azotemic. Serum electrolyte changes included hyperkalemia (n = 215), hyponatremia (183), hypochloremia (94), and hypercalcemia (69). Five of the 220 dogs with primary hypoadrenocorticism and the 5 dogs with secondary hypoadrenocorticism did not have hyperkalemia at time of diagnosis. In all dogs, ACTH stimulation testing revealed a low to low-normal baseline serum cortisol concentration with little to no rise after ACTH administration. Endogenous plasma ACTH concentration measured in 35 dogs with primary hypoadrenocorticism was markedly high; whereas ACTH concentration was undetectable to low in the 5 dogs with secondary hypoadrenocorticism. Clinical Implications: Hypoadrenocorticism is a rare disease in dogs, most commonly affecting young to middle-aged females; some breeds are at greater risk of developing the disease than others. In general, clinical signs are nonspecific and similar to manifestations of more common diseases. Serum electrolyte disturbances of hyperkalemia and hyponatremia are characteristic in dogs with primary hypoadrenocorticism, but concentrations may be normal in dogs with early or mild primary or secondary hypoadrenocorticism. Diagnosis of hypoadrenocorticism is best confirmed by demonstration of a low baseline serum cortisol concentration with a subnormal or negligible response to ACTH administration. Determination of endogenous plasma ACTH concentrations is valuable in differentiating primary from secondary hypoadrenocorticism, particularly in dogs with normal serum electrolyte concentrations.

SUMMARY: Hyperthyroidism was diagnosed in 131 cats during a 3½-year period. The cats ranged in age from 6 to 20 years; there was no breed or sex predilection. The most frequent clinical signs included weight loss, polyphagia, increased activity, polydipsia, polyuria, and vomiting. Common serum biochemical abnormalities included high values for alkaline phosphatase activity (75%), lactate dehydrogenase activity (66%), aspartate transaminase activity (66%), and alanine transaminase activity (54%). Electrocardiographic changes included tachycardia (≥240 beats/min) and increased R-wave amplitude in lead II (≥0.9 mV) in 66% and 29% of the 131 cats, respectively. Thoracic radiography in 82 cats revealed cardiomegaly in 40 (49%) of these cats; 16 cats with congestive heart failure also had pulmonary edema or pleural effusion. In 5 cats with markedly increased fecal volume, mean 48-hour fecal fat content was significantly greater than normal, with daily fat excretion 2 to 15 times the upper limit of normal. Base-line serum thyroxine concentrations were increased above normal range in all cats, whereas triiodothyronine concentrations were increased in 127 (97%) of the 131 cats. In 11 cats tested, mean thyroxine concentration did not increase significantly after thyroid-stimulating hormone administration. Mean 24-hour percentage of thyroid radioiodine uptake in 32 hyperthyroid cats was significantly higher (39.1%) than normal (9.2%). Thyroid scans, performed on 126 cats, showed enlargement and increased radionuclide accumulation in 1 thyroid lobe in 36 (29%) and both lobes in 90 (71%) of the cats.

Objective: To determine whether measurement of baseline serum concentrations of total thyroxine (T₄), triiodothyronine (T₃), free T₄, and thyrotropin (thyroid-stimulating hormone; TSH) would aid in the diagnosis of hypothyroidism in dogs. Design: Prospective case series. Animals: 54 dogs with hypothyroidism, 54 euthyroid dogs with nonthyroidal disease initially suspected to have hypothyroidism, and 150 clinically normal dogs. Procedure: In the 54 dogs with hypothyroidism, diagnosis was established on the basis of clinical signs, results of routine laboratory and TSH stimulation tests, exclusion of concurrent nonthyroidal disease, and a good clinical response to treatment with l-thyroxine. Blood samples were collected from all dogs and were tested for thyroid hormone and TSH concentrations. Reference ranges for hormone concentrations were established on the basis of results for the 150 clinically normal dogs. Results: Of the 54 hypothyroid dogs, 48 (89%) had low total T₄ concentrations, 3 had low-normal concentrations, and 3 had high concentrations because of T₄ autoantibodies. In contrast, only 10 (18%) euthyroid dogs had low total T₄ concentrations. Only 3 of 31 (10%) hypothyroid dogs had low T₃ concentrations; 23 had concentrations within the reference range, and 5 had high concentrations because of T₃ autoantibodies. Only 3 of 38 euthyroid dogs had low T₃ concentrations. Of the hypothyroid dogs, 53 (98%) had low free T₄ concentrations and 1 had a low-normal concentration. Only 4 (7%) euthyroid dogs had low free T₄ concentrations. Of the hypothyroid dogs, 41 (76%) had high TSH concentrations, and 13 had TSH concentrations within the reference range. Of the euthyroid dogs, only 4 (8%) had high TSH concentrations. Of all single hormone measurements evaluated, measurement of free T₄ concentration had the highest sensitivity (0.98), specificity (0.93), and accuracy (0.95) as a test for hypothyroidism; measurement of total T₄ concentration had a lower sensitivity (0.89), specificity (0.82), and accuracy (0.85). Compared with measurement of total or free T₄ concentration, measurement of TSH concentration had a lower sensitivity (0.76) and accuracy (0.84) but specificity (0.93) equal to that for measurement of free T₄ concentration. When T₄ (total or free) and TSH concentrations were evaluated together, specificity was higher than when T₄ or TSH concentration was evaluated alone. Only 1 euthyroid dog had low T₄ (total and free) and high TSH concentrations. Clinical Implications: Results indicate that measurement of serum free T₄ and TSH concentrations is useful for diagnosis of hypothyroidism in dogs. About a quarter of the dogs with confirmed hypothyroidism, however, will have serum TSH concentrations within reference limits. (J Am Vet Med Assoc 1997;211:1396–1402)

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)