Introduction
Because it often afflicts middle-aged to older dogs, Cushing’s disease can fool owners who think they’re simply seeing the natural effects of old age on their pet. However, if diagnosed properly and promptly, Cushing’s usually can be managed in a way that either eliminates it or mitigates its severity and greatly improves the dog’s quality of life.
Cushing’s disease is caused by excess production of one or more of the hormones (called adrenocorticoids, adrenocorticosteroids or adrenal steroids) that are produced by the adrenal glands. Cushing’s is most commonly caused by the excess production of cortosol. By far the most common form of the disease is caused by tumors on the pituitary – this is called Pituitary Dependent Hyperadrenocorticism, or “PDH.” Cushing’s disease can also be caused by a tumor on the adrenal glands, which is called Adrenal Tumor Hyperadrenocorticism, or “ATH.” Finally, Cushing’s can be caused by drugs given for other ailments that stimulate excessive adrenal hormone production; this type of Cushing’s is called “iatrogenic.”
Since Cushing’s is largely treatable, and possibly curable, recognizing the clinical signs is critical to a pet’s prognosis.
Symptoms of Cushing's Disease in Dogs
Hyperadrenocorticism, or Cushing's Disease, is most commonly seen in dogs over 6 years of age, with only a slight predisposition for female dogs, although dogs as young as 1 year have been diagnosed. Cushing’s appears more frequently in small dogs (most weigh less than 20 kg). Beagles, Boxers, Dachshunds, German Shepherds, Labrador Retrievers, Poodles and some breeds of Terriers (especially Boston Terriers) seem to be overrepresented.
The most common clinical signs of Cushing’s disease are: increased water intake (polydipsia) and the resulting increase in urination (polyuria), increased appetite/eating (polyphasia), weight gain, panting, abdominal enlargement (seen as a pendulous belly), excessive skin bruising, symmetrical hair loss (alopecia), exercise intolerance, weakness/lethargy, possible muscle atrophy and/or obesity. Several, but not all, of these signs usually appear together. As the disease progressive, affected dogs normally show additional signs.
On physical examination, the veterinarian often notices thin or fragile skin that tears easily, an enlarged liver (hepatomegaly), hypertrophy or atrophy of male/female genitalia and sometimes neurologic signs like lack of coordination, circling, aimless wandering or pacing.
Owners may report that their dog has suddenly started urinating in the house, even though it has been housebroken for years. Cortisol increases appetite and thirst, so owners may notice that they are filling their dog’s food and water bowls much more often than usual, and in fact may report that their pet’s appetite is ravenous. Likewise, they often report abnormal hair loss that is symmetrical on both sides of their dog’s body, along with loss of muscle mass especially in the legs. Muscle atrophy and corresponding redistribution of weight often give dogs with this disease a “pot-bellied” look. They also commonly have poor wound healing.