Laboratory diagnosis and treatment of hyperadrenocorticism in dogs (Proceedings)
Cushing's syndrome refers to all causes of hyperadrenocorticism with overproduction of cortisol.
a. ACTH-dependent1) Cushing's disease: Pituitary hypersecretion of ACTH which results in bilateral adrenal hyperplasia (90% of cases)
2) Ectopic ACTH production: Non-pituitary tumors secreting ACTH resulting in bilateral adrenal hyperplasia. Has not been completely documented in dogs or cats.
b. ACTH independent
1) Adrenocortical adenoma or carcinoma: Hypersecretion of cortisol with atrophy of normal adrenal and suppressed ACTH concentrations (10% of cases).
1) Excessive or prolonged administration of glucocorticoids. Clinically indistinguishable from natural disease. Results in adrenal atrophy and suppressed ACTH levels.
a. Poodles, Dachshunds, Schnauzers, Boston Terriers, Boxers.
b. Middle to old age. Average 12 years; range 6 months to 17 years.
c. No sex predilection.
d. Rare in cats. Usually seen with insulin resistant diabetes mellitus and/or cats with severe dermal atrophy/ulceration.
3. Clinical Signs
a. PU / PD
b. Pendulous, "pot-bellied abdomen": Due to muscle catabolism by glucocorticoids and hepatomegaly.
c. Bilaterally symmetric alopecia: Head and extremities spared.
d. Thin skin
e. Muscle weakness and muscle atrophy; cruciate ruptures
f. Mineralization of skin (calcinosis cutis)
g. Hyperpigmentation: ACTH similar to MSH, co-existing hypothyroidism, chronic skin irritation.
h. Reproductive abnormalities
2. Clitoral hypertrophy
3. Testicular atrophy
4. Perianal adenomas in females and neutered males.
i. Respiratory signs
1. Panting: Pulmonary hypertension and decreased compliance, primary CNS disturbance, pulmonary mineralization.
2. Dyspnea: Rare; seen with pulmonary thromboembolism and concurrent congestive heart failure.
j. Central nervous system
1. Seen with large pituitary tumors (macroadenomas). Present at time of diagnosis or following therapy for Cushing's disease as microscopic pituitary tumors enlarge into macroadenomas.
2. Signs due to compression/invasion of pituitary and/or hypothalamus:
v. Behavior change
vi. Head pressing
4. Diagnosis of Hyperadrenocorticism
a. History and clinical signs
b. R/O iatrogenic disease with questions concerning current or past medications. These medications can include oral, ophthalmic, otic, and topical medications. Make sure the owner tells you about everything and anything that went on or in their pet.
c. Laboratory data
A. Polycythemia (PCV 45-55%)
b. Stress leukogram