Hyperadrenocorticism (Cushing's Syndrome) in Cats
Dr. Douglas Brum
CBC. The CBC evaluates the red blood count for anemia and the white blood count for any abnormalities. No consistent findings in the CBC are typical in the cushingoid cat; however, the CBC remains important in determining any problems that might be associated with disease. Anemia and evidence of chronic infections might be noted.
The diagnosis of feline Cushing's syndrome is very difficult to achieve accurately. The diagnosis should always be made on the basis of the clinical suspicion and then supported with the appropriate diagnostics. The most common reason to suspect feline Cushing's syndrome is insulin-resistant diabetes. Diagnostic tests that are important in evaluating a potential cat with Cushing's syndrome include:
Biochemical profile. The most consistent lab abnormality in feline Cushing's disease is an elevated blood glucose associated with diabetes. The alkaline phosphatase enzyme, so often elevated in dogs, is elevated in about 1/3 of cats, but this may also be elevated from the concurrent diabetes. Cats lack the specific steroid-induced isoenzyme found in the dog that produces the increase in this enzyme. Other liver enzymes and cholesterol may also be elevated in the cushingoid, diabetic cat.
Urinalysis with culture and sensitivity. Most cats with Cushing's syndrome have glucose in their urine, due to the poorly regulated diabetes. This combined with the suppression of the immune system, caused by the elevated cortisol levels, makes the cat susceptible to urinary tract infections.
X-rays of the chest and abdomen evaluate for any evidence of metastatic cancer. It would be rare to visualize an adrenal tumor, but X-rays remain as an important diagnostic in getting an overall health assessment of the cat.
Blood pressure measurement. Chronic evaluations in cortisol levels may lead to elevations in blood pressure (hypertension).
Abdominal ultrasound. An abdominal ultrasound is a very useful diagnostic aid in evaluating the size and shape of the liver, and especially adrenal glands. A single enlarged adrenal gland would be indicative of a primary adrenal tumor. Bilateral enlargement would suggest adrenal hyperplasia or enlargement due to a pituitary tumor.
ACTH stimulation test. The pituitary hormone ACTH is injected into the cat and cortisol levels are measured pre- and post-injection. Ideally, the cushingoid cat would have an exaggerated response to ACTH, with the post-cortisol level being elevated above the normal. Unfortunately, there are significant false positive readings (cats without Cushing's that test positive) and false negatives (cats with Cushing's that test negative). The test needs to be evaluated with caution.
Dexamethasone suppression testing. Normally, dexamethasone causes a decrease of cortisol production by the adrenals. In cats with Cushing's syndrome, the normal suppression of the cortisol is usually not seen when low doses of dexamethasone are used. Low dose dexamethasone suppression testing in the cat requires a higher dosage of dexamethasone than commonly used in dogs, thus a high dose test is used in attempting to diagnose the disease.
Dexamethasone suppression/ACTH stimulation test. A protocol for combining both of these tests has been described and may provide stronger evidence for a diagnosis of feline Cushing's syndrome.
ACTH levels. The direct blood measurement of ACTH requires proper sample handling and a specialized laboratory to run the sample. ACTH levels are not be used to diagnosis Cushing's syndrome; rather, they are useful in differentiating pituitary from adrenal hyperadrenocorticism. Normal to elevated levels suggests pituitary dependent disease. Very low levels of ACTH correlate with a primary adrenal tumor.
CT or MRI evaluation of the pituitary or adrenal glands is a useful tool in assessing for potential tumors but require referral to a specialized center.
Feline hyperadrenocorticism is a very debilitating disease. Stabilizing any secondary complicating diseases should be attempted before treating the Cushing's disease. Concurrent urinary tract infections require antibiotics. Diabetes is often difficult to regulate appropriately, but attempts to stabilize and decrease blood sugar to the safest levels should be attempted. Since feline Cushing's syndrome is so uncommon, only a limited number of cats have been managed. Medical therapy with a variety of drugs has been shown to be of only limited value. The surgical option seems to provide the best long-term prognosis for these cats. Treatment options that have been tried include:
O, p'-DDD (Lysodren) is the most useful drug in treating canine Cushing's syndrome. Unfortunately, cats are fairly resistant to the drug, even at high dosages.
Ketoconazole is an enzyme blocker that blocks the synthesis of cortisol in people and in dogs. It is not effective in cats.
Metyrapone is also an enzyme blocker and might be the most effective medical therapy in cats. Unfortunately very few cats have been tried on this drug, and the drug is not readily available.
Surgical management is the most effective treatment option. Unfortunately, many cushingoid cats are fragile surgical candidates that require very close pre- and post-operative monitoring and requiring 24- hour care. Since the goal of surgery is to remove one or both of the adrenal glands, a rapid decrease occurs of both the elevated glucocorticoids and normal mineralocorticoids, which are other hormones, specifically aldosterone, that are produced in the adrenal gland that maintain electrolyte balance. This leads to most of the surgical and post surgical metabolic complications. In order to minimize this effect both glucocorticoid and mineralocorticoid replacement therapy are given pre-operatively and continued post-operatively. If an adrenal tumor is suspected, and confirmed at surgery, the single adrenal gland is removed.
If pituitary dependent Cushing's disease is confirmed, then both adrenals are removed. Intravenous fluids are given aggressively, as well as intravenous nutrition. In the diabetic patient, the blood sugar needs to be carefully monitored, and fast acting regular insulin is given as needed. Postoperative antibiotics are commonly given, as sepsis (blood infection) is a common complication. Blood electrolytes (specifically potassium, sodium and chloride) need to be monitored closely and medication adjusted to stabilize their levels. Managing the postoperative cat is challenging and usually requires specialized care.