The adrenal glands of dogs with Cushing’s disease (hyperadrenocortism) produce excessive amounts of cortisol, a hormone with potent anti-inflammatory and immuno-suppressive effects.
There are three basic causes of Cushing’s disease . These include pituitary-dependent hyperadrenocorticism, adrenocortical cancer, and iatrogenic (medically induced) hyperadrenocorticism.
About 85 percent of dogs with Cushing’s have an overactive pituitary gland which is a small pea sized gland in the brain producing an excessive secretion of a hormone ACTH. This in turn, overstimulates the adrenal glands to produce cortisol in excess. The majority of the remaining cases result from adrenal tumors. About 50 percent of the adrenal tumors are benign. Iatrogenic hyperadrenocortism is due to prolonged administration or cortisone. These medications are used to treat a variety of illness in dogs.
Cushing’s disease is usually seen in middle aged to older dogs, and some breeds, such as Boston terriers, poodles, dachshunds, boxers, Scotties, and German shepherds, seem to be genetically predisposed to it. All breeds, however, can be affected.
The signs of Cushing’s include hair loss, excessive drinking and urination, exercise intolerance, pot-bellied abdomen, chronic infections, bilateral symmetrical hair loss. But because these signs are not specific to Cushing’s, veterinarians have to perform several laboratory tests to confirm the disease and then determine its exact cause. Some dogs with Cushing’s disease will also develop diabetes.
As stated before, most of patients suffer from the pituitary form of Cushing’s. In such cases, medication can help dogs live out their years in healthy hormonal balance. Lysodren, the brand name for a drug that destroys some of the cortisol-producing adrenal cells, is the drug most frequently used to treat this disease.
The goal is to normalize cortisol levels without creating a cortisol deficiency, which would also adversely affect health.
Although standard protocols and doses are used, it is impossible to predict what dose of Lysodren will work for an individual dog. The administration protocol involves an initial loading or induction phase. This involves giving the medication daily until clinical signs resolve. The most common sign used is a decrease in water consumption. Then a maintenance phase is developed that uses a dosage once or twice weekly.
Throughout treatment – and especially during the 5 to 14 day induction phase – owners need to closely watch their dogs for listlessness, loss of appetite, vomiting, and diarrhea – indications that cortisol levels have fallen too low. If an owner notices these signs, he or she must give the dog cortisone, a cortisol derivative. (Owners caring for a dog on Lysodren should always keep cortisone pills on hand.)
Periodic laboratory tests and Lysodren dosage adjustments will probably be made during the lifelong treatment of Cushing’s disease. About 50 percent of dogs treated for the pituitary form of Cushing’s will relapse at some point, and about 33 percent experience an adverse reaction to Lysodren.
Other medical options are available for the treatment of Cushing’s disease.. One alternative is ketoconazole, an antifungal drug that interrupts cortisol synthesis in the adrenal glands. While this drug is usually effective and more predictable than Lysodren, it is also much more expensive. In addition, 1-deprenyl, a drug that represses the overactive pituitary is now available. This new therapy is also more expensive the Lysodren on a per dose basis, but does not require the expensive monitoring needed with Lysodren.
A medicine showing promise for the treatment of Cushing’s is now available. This medication is called “Trilostane (Vetoryl). This drug is available in the United States for dogs and also available in England for humans under the name Moderal. It works by blocking adrenal gland production and as with Lysodren will require monitoring of the adrenal glands by blood tests.
Cushing’s disease is complex and may be difficult to fathom initially. But most owners discover that treating and monitoring their dog becomes second nature before long.