Dear Dr. Thompson: On a routine visit to the vet, my dog had elevated alkaline phosphate. The vet said she probably had Cushing s. What is Cushing s? What are the signs and symptoms? What should I expect the disease to do to my dog?
ANSWER: Cushing s disease is one of the more common hormonal diseases affecting older dogs. It is a result of the body over-producing the stress hormone cortisol. Cortisol is a steroid hormone produced in the outer layer of the adrenal gland. It is not the type of steroid that athletes abuse, but rather one the body produces in response to stressful situations.
The majority of cases of Cushing s disease, also called hyperadrenocorticism, involve a benign tumor in the pituitary gland in the brain sending excess hormones to the adrenal glands that stimulates them to produce significantly more cortisol than the body needs. Less than 20 percent of cases result from an active cancerous tumor growing on one of the adrenal glands.
The disease has a very slow progression and many people do not realize the changes in a pet that have occurred over months or years. Common symptoms include excessive thirst and urinations, heavy panting, weight gain, ravenous appetite and skin and hair coat changes.
These are all a direct result of the hormone s long-term impact on the body. Other conditions can develop secondarily to Cushing s disease. These include type 2 diabetes, liver disease, recurring urinary tract and skin infections, and high blood pressure.
Diagnosing the disease has some pitfalls. The symptoms mimic many other conditions, and the secondary diseases can shift the focus to those problems while the underlying root problem like Cushing s is overlooked.
The changes your veterinarian found on screening blood tests are typically the first step in establishing the diagnosis. The blood enzyme called alkaline phosphatase will be elevated in more than 90 percent of dogs with Cushing s. However, this alone does not confirm your dog has Cushing s, and further testing is needed.
A screening test on your dog s urine is very helpful to determine if your dog does not have the disease.
If the screening test on the urine is positive, one of two special blood tests are used to diagnose Cushing s disease. However, in a percentage of cases it will not establish whether the problem is a result of the benign tumor in the pituitary gland or the cancerous tumor on the adrenal gland, and an ultrasound may be needed to see if one or both glands is enlarged.
Treatment involves drug therapy to knock out the hormone producing layers of the adrenal glands. Historically there was only one choice for treatment; a drug called Lysodren. It is very effective but can have side effects during the initial phase of treatment. A newer drug, trilostane, has been used in Europe for years to treat this condition and it is currently in the approval process for use in the United States.
This drug has showed promise due to its relatively fewer serious side effects during the early treatment stages.
As you can see, this is a complicated disease with a complicated diagnostic and treatment process. Unchecked, this disease will dramatically shorten your dog s life span. When treated, many dogs do great and their quality of life is exponentially improved.
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