Peter P. Kintzer

Radiographic findings in dogs with naturally-occurring primary hypoadrenocorticism

Survey radiographs often are obtained in dogs with primary hypoadrenocorticism in adrenal crisis as part of the routine evaluation of a critically ill dog. In this study, standardized methods of cardiac, pulmonary vasculature, and vena cava mensuration were used in 22 dogs with naturally-occurring primary hypoadrenocorticism, and the findings were compared with those in 22 breed-matched, clinically normal dogs. Most (81.8%) untreated dogs with primary hypoadrenocorticism had one or more radiographic abnormalities, including small size of the heart (45.5%), cranial lobar pulmonary artery (36.4%), caudal vena cava (54.5%), or liver (36.4%). Megaesophagus was not found in any of the dogs with hypoadrenocorticism, and therefore, compared to the other common radiographic findings, should be considered a rare finding.

Nuclear Medicine of the Thyroid Gland: Scintigraphy and Radioiodine Therapy

Nuclear medicine may have both diagnostic and therapeutic utility during the evaluation and management of thyroid disease. This article will focus on the use of radionuclide scintigraphy and radioactive iodine therapy in the diagnosis and treatment of thyroid disease in the dog and cat.

Primary and secondary canine hypoadrenocorticism.

Hypoadrenocorticism (primary or secondary) is an uncommon endocrine disorder seen most commonly in young-to-middle-aged female dogs. This article reviews the various clinical manifestations of this disorder, recommended testing protocols for definitive diagnosis, and current therapeutic protocols. The long-term prognosis is good-to-excellent for most dogs receiving appropriate replacement therapy.

Considerations in the Treatment of Feline Hyperthyroidism

Feline hyperthyroidism can be treated with long-term antithyroid drug administration, surgical thyroidectomy, or radioactive iodine. This article discusses the advantages of each of these treatment options and gives specific recommendations on the use of each therapeutic modality.

Medical Treatment of Pituitary-Dependent Hyperadrenocorticism: Mitotane

Mitotane (o,p-DDD; Lysodren) is the drug most commonly used to treat dogs with pituitary-dependent hyperadrenocorticism. Although variations of the original protocol, suggested more than 20 years ago, have been reported, most clinicians still use an initial loading dose of mitotane followed by a weekly maintenance dose. Although a gratifying response to treatment is seen in most dogs, some dogs are neither easy nor straightforward to treat and present the practitioner with one or more therapeutic challenges, including failure to respond adequately, development of adverse effects, or development of relapse during treatment. Nevertheless, with careful management and follow-up, such problems can be overcome and a successful outcome achieved in most cases.

Effect of spontaneous hyperadrenocorticism on endogenous production and utilization of glucose in the dog

Alterations in carbohydrate metabolism were evaluated in 15 dogs with untreated hyperadrenocorticism by measuring basal plasma concentrations of glucose and insulin and determining the rates of hepatic glucose production and overall glucose uptake by tissues using 6-3H-glucose as the tracer. Of the 15 dogs, 8 (53%) had fasting hyperglycemia and 12 (80%) had insulin resistance, evidenced by mild to severe endogenous hyperinsulinemia together with euglycemia or hyperglycemia. Mean rates of both hepatic glucose production (323.1 mg/kg/hr) and tissue utilization of glucose (319.2 mg/kg/hr) were significantly (P<0.001) increased in the dogs with hyperadrenocorticism, compared to the glucose turnover rate in normal dogs (169.9 mg/kg/hr). Despite the increased glucose utilization rates, the mean rate of glucose clearance remained normal in the dogs with hyperadrenocorticism. n nIn 6 dogs re-evaluated after treatment of hyperadrenocorticism, insulin resistance and glucose intolerance improved or resolved, evidenced by decreases in the mean plasma concentrations of both insulin and glucose into the normal range. After correction of glucocorticoid excess and associated insulin resistance, elevated rates of glucose production and utilization also decreased significantly (P<0.005) and normalized in all dogs. n nIn results of this study indicate that increased glucose production and utilization are characteristic of spontaneous canine hyperadrenocorticism. Despite the increased rates of glucose tissue uptake, the normal glucose clearance rates found in these dogs suggest relative impairment of overall glucose utilization. Nevertheless, it appears that hepatic glucose overproduction plays the major role in the development of the hyperglycemia commonly associated with canine hyperadrenocorticism.

DIAGNOSIS AND MANAGEMENT OF CANINE CORTISOL-SECRETING ADRENAL TUMORS

Cortisol-secreting adrenal tumors are responsible for 10% to 15% of all cases of naturally occurring canine hyperadrenocorticism. Differentiation of adrenal-dependent hyperadrenocorticism from pituitary-dependent hyperadrenocorticism is very important because the recommended therapeutic approaches for each are different, and the prognosis also may be different. A stepwise approach to diagnosing and staging the disease is needed. Treatment options include surgery and administration of mitotane or ketoconazole.