Cushing’s Disease In Dogs:
Cushing's Disease (Hyperadrenocorticism) Is A Disease Of Middle-age And Older Dogs
Typical signs of Cushing's disease in dogs: heightened water consumption resulting in increased urination, intensified appetite, hair loss, potbellied appearance. Dogs with Cushing’s disease are more susceptible to infections of the mouth, ears, skin and urinary tract.
Owners often attribute the changes to "old age”, having the dog evaluated on noticing hair loss (alopecia) or thinning of the skin. Hair loss starts at the elbows and progresses to the flanks and abdomen until eventually only the head and extremities have hair. Another common symptom of Cushing’s disease in dogs is increased water consumption 2-10 times the normal amount, resulting in increased urination (polyuria/polydipsia). Housebroken dogs may have accidents because their bladders fill with an overproduction of urine. Increase in appetite (polyphagia) is another common symptom in approximately 80% of dogs with Cushing’s disease. Habit changes observed are: stealing food, getting into garbage, begging continuously, becoming protective of food. In a majority of affected dogs, abdominal enlargement is noticed, resulting from shifting of fat to the abdominal area and weakening/wasting of muscle mass in the abdomen.
Cushing’s disease in dogs is a complicated disease with wide range of symptoms and causes.
The pituitary gland produces the hormone ACTH, which stimulates the adrenal gland to produce the steroid hormone glucocorticoid (cortisone-like or cortisol). Cushing’s disease in dogs develops when too much glucocorticoid is produced, resulting in a chronic overproduction of cortisol into the bloodstream. Cortisol helps the body respond to stress, and impacts blood sugar levels, fat metabolism, skeletal muscles, kidney function, nervous system, cardiovascular system, and immune response. A chronic excess of blood cortisol means the dog is being poisoned with too much cortisol and cannot rely on its own feedback mechanism to regulate the blood cortisol level.
The evaluation of any dog suspected of having Cushing's disease should include a complete blood count, chemistry profile and urinalysis.
Screening tests include: urine cortisol, creatinine ratio (further diagnostics are required if this test is abnormal), low dose dexamethasone suppression test (normal dogs show a marked decrease in blood cortisol levels within 8 hours of being given low doses of dexamethasone, 90% of affected dogs do not show a decrease), and ultrasound (to evaluate all of the abdominal organs). Abnormalities in these tests include: increased alkaline phosphatase, increased ALT (liver enzymes), increased cholesterol, decreased BUN (a kidney function test), and dilute urine.
Diagnosis of Cushing's disease in dogs should never be made based only on laboratory tests.
The dog needs to show symptoms and have a medical history consistent with the diagnosis. If an adrenal tumor is identified, surgical removal may be a viable option. About 80% of Cushing's disease in dogs is the pituitary type. Since both the adrenal and the pituitary types will respond effectively to oral treatments, many veterinarians do not perform the diagnostics to distinguish between the two different forms.
Lysodren (generic mitotane) is a treatment for pituitary-dependent Cushing's disease in dogs. Lysodren is like chemotherapy in that it works by destroying cells of the adrenal gland that produce the corticosteroid hormones. It is convenient to use, relatively inexpensive, and probably the most used treatment. The downside is possible serious side effects. Regular blood-monitoring during the initial phase of therapy and close communication between vet and owner are required.
Trilostane: A newer drug used to treat some dogs with Cushing's disease without some of the side effects caused by mitotane. It is more expensive, but may be an alternative treatment for dogs with adrenal tumors. The dog is examined repeatedly during the initial phase of treatment, and ACTH stimulation tests are performed. In many cases, after several months of therapy the dose needs to be increased.
The right diet can mean the difference between a strong immune system and a weak one, to fight Cushing's disease in dogs.
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