Cushing’s Disease

Animal bodies are a marvel of interactions between organs and systems kept in balance by the production of enzymes that aid in metabolic processes and hormones that regulate body functions. When the balance is disturbed by illness, injury, or advancing age, the body goes awry: appetite and water consumption may change, organs may malfunction, or medication to treat one illness may cause another.

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.

Located above the kidneys, the adrenals produce cortin, a complex of steroid hormones - including cortisone and cortisol - that help regulate body weight, mineral balance, the structure of connective tissue, some white blood cell production, and skin health. Adrenocorticotropic hormone (ACTH) from the pituitary gland stimulates the adrenal glands to produce cortin. Presence of a tumor on either the adrenal glands or pituitary can cause the adrenals to run amok and trigger Cushing's by producing an excess of cortin.

Diagnosis

The symptoms may creep up on the pet and pet owner. Pets do not appear to be critically ill because the danger signs of vomiting, diarrhea, pain, seizures, and bleeding do not occur. To the contrary, the symptoms often appear to be connected to normal aging. Muscle weakness also causes lethargy and a reduced tolerance for exercise, 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.