Such is the case with Cushing's disease, also known as hyperadrenocorticism, the production of excess hormones from the adrenal glands. Cushing's disease usually strikes older dogs with a bucket-full of symptoms that can mimic other diseases. Increased appetite, increased drinking and urination, panting, high blood pressure, bulging abdomen, skin lumps and discoloring, hair loss, muscle weakness, and nervous system disorders can occur with the disease.
The adrenal glands are located above the kidneys. The adrenals produce cortin, a complex of steroid hormones that help regulate body weight, mineral balance, the structure of connective tissue, some white blood cell production, and skin health. Adrenal glands are stimulated to produce cortin by adrenocorticotropic hormone (ACTH) from the pituitary gland. Cushing's disease can be triggered by a tumor of the adrenal glands or of the pituitary gland; either one can cause the adrenal glands to run amok and produce an excess of corticosteroids.
Diagnosis
The symptoms may creep up on the pet and pet owner. The danger signs of vomiting, diarrhea, pain, seizures, and bleeding do not occur; the pets do not appear to be critically ill. To the contrary, the symptoms often appear to be connected to normal aging. Muscle weakness also causes a reduced tolerance for exercise and lethargy, both of which are typical in aging dogs and cause no alarm in owners. Often owners do not seek veterinary advice until the signs become unmistakable or intolerable — when the dog breaks his housetraining or begs to go outside during the night for example.
The typical Cushing's dog has a bulging, sagging belly caused by a decrease in muscle strength and redistribution of fat from body storage areas to the abdomen. As the disease progresses, hair loss may also become a major concern and the skin thins and may lose its resistance to infection.
Once suspected, Cushing's disease can be diagnosed by blood tests. Once it is diagnosed, tests can also differentiate between disease caused by pituitary gland tumor and disease caused by adrenal gland tumor.
About 85 percent of the cases are caused by pituitary tumors. Pituitary-induced Cushing's can be treated by drug therapy, but it cannot be cured. Adrenal gland tumors can often be surgically removed.
There are several drug therapies available, including Lysodren, Ketoconazole, and Anipryl®. Lysodren kills the outer layer of the adrenal gland that manufactures the corticosteroids. Careful regulation of the drug determines how much of the cortex is killed so that a normal amount of the hormone can be produced. This protocol requires periodic blood tests to make sure the dog has a normal amount of cortisol and does not develop Addison's disease. Once the proper dosage has been determined, the dog's condition may be maintained by periodic instead of daily doses.
Ketoconazole works by suppressing cortisol secretion in the adrenal glands. It requires daily dosing, monitoring, and acute observation by the pet owner, and is expensive. Some dogs cannot absorb it, rendering it useless in 20-25 percent of cases. It is useful for dogs that cannot tolerate Lysodren, has a low incidence of toxicity, and is completely reversible if necessary.
Anipryl® was approved for use in canine Cushing's disease in June 1997. Anipryl® helps restore the balance of natural brain chemicals which in turn alleviate the symptoms of the disease. In clinical trials, about 70 percent of dogs responded favorably with a lessening of symptoms and a reduction in cortisol production.
Left untreated, Cushing's disease will progress and can lead to life-threatening disorders such as diabetes, congestive heart failure, and liver and kidney failure, and to chronic maladies such as hypothyroidism and infections of the skin, ears, gums, eyes, or bladder. If your pet exhibits any of the early signs of Cushing's and is six years old or older, make an appointment with your vet right away. Pituitary Cushing's disease cannot be cured, but the treatments available can prolong your pet's quality of life and keep him around for years longer. If an adrenal tumor is causing the disease, surgery may be indicated. Either way, it's better to get started on treatment.
