PRETREATMENT CLINICAL AND LABORATORY FINDINGS IN DOGS WITH HYPOADRENOCORTICISM - 225 CASES (1979-1993)

Objective-To evaluate clinical and laboratory findings in 225 dogs wit h naturally occurring hypoadrenocorticism diagnosed over a 14-year per iod. Design-Retrospective case series. Animals-220 dogs with primary h ypoadrenocorticism and 5 dogs with secondary hypoadrenocorticism (prim ary ACTH deficiency).Procedure-We reviewed medical records of all dogs with naturally occurring hypoadrenocorticism examined at The Animal M edical Center between 1979 and 1993 or at Tufts University, Foster Hos pital for Small Animals, between 1987 and 1993. Results-Dogs ranged fr om 4 months to 14 years old. Most (71%) were female, and female dogs h ad a significantly higher relative risk of developing hypoadrenocortic ism than did males. Great Danes, Portuguese Water Dogs, Rottweilers, S tandard Poodles, West Highland White Terriers, and Wheaten Terriers ha d a significantly higher relative risk of developing hypoadrenocortici sm than did dogs of other breeds. Common owner complaints included let hargy, poor appetite, and vomiting, whereas lethargy, weakness, and de hydration were common abnormalities detected on physical examination. Serum biochemical testing at the time of diagnosis revealed moderate-t o-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), hypochlo remia (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 stim ulation testing revealed a low to low-normal baseline serum cortisol c oncentration with little to no rise after ACTH administration. Endogen ous plasma ACTH concentration measured in 35 dogs with primary hypoadr enocorticism was markedly high; whereas ACTH concentration was undetec table to low in the 5 dogs with secondary hypoadrenocorticism. Clinica l Implications-Hypoadrenocorticism is a rare disease in dogs, most com monly affecting young to middle-aged females; some breeds are at great er risk of developing the disease than others. In general, clinical si gns are nonspecific and similar to manifestations of more common disea ses. Serum electrolyte disturbances of hyperkalemia and hyponatremia a re characteristic in dogs with primary hypoadrenocorticism, but concen trations may be normal in dogs with early or mild primary or secondary hypoadrenocorticism. Diagnosis of hypoadrenocorticism is best confirm ed by demonstration of a low baseline serum cortisol concentration wit h a subnormal or negligible response to ACTH administration. Determina tion of endogenous plasma ACTH concentrations is valuable in different iating primary from secondary hypoadrenocorticism, particularly in dog s with normal serum electrolyte concentrations.