Cushing’s disease is a hormonal disease that typically occurs in middle age to older dogs. The medical term for Cushing’s is “hyperadrenocorticism”, and that’s exactly what it is – a hyperactive adrenal gland, causing overproduction of cortisol. The disease occurs because either there’s a tumor on the pituitary gland in the brain (pituitary-dependent Cushing’s) or on the adrenal gland itself. The end result is the same, regardless, and the excessive production of cortisol results in a host of problems.
Dogs can also get Cushing’s disease when they are medicated for long periods of time with drugs that mimic cortisol in the body– this is called “iatrogenic Cushing’s” which means that it was caused by giving medication. For this discussion, however, we’ll focus on the main types. Cats can also get Cushing’s disease, and it’s typically iatrogenic when they do.
Fortunately, there are lots of symptoms of Cushing’s disease that owners can recognize at home. Perhaps unfortunately, however, these signs are also similar to the signs associated with several other diseases, and it sometimes takes several tests to put together a definitive diagnosis. Let’s review what you might see at home in your dog that should prompt you to discuss his symptoms with your vet.
Polyuria and polydipsia
These are fancy words, but what they really mean are increased urination and increased drinking.
We often abbreviate them “PU/PD”. Diabetes, some types of cancer, kidney disease, liver disease – lots of other diseases can cause PU/PD, so when we observe it in a dog we have some work to do to figure out what’s causing it.
The mechanism that’s driving the PU/PD is different depending on the disease that’s causing it. In Cushing’s the dog has primary PU and secondary PD, meaning it causes excessive production of urine, which in turn results in increased thirst.
Polyphagia and subsequent weight gain with muscle loss
Here’s another fancy word, and another symptom of other diseases besides Cushing’s. Polyphagia means increased appetite and frequency of eating, which also occurs in dog with diabetes. The difference with Cushing’s disease is that the dog tends to gain weight, and with diabetes the dog loses weight. Some types of cancer also cause increased appetite but again, typically the dog is losing weight at the same time.
Again, the overproduction of steroid hormones is behind these clinical symptoms. Cortisol stimulates the breakdown of proteins, which in turn makes the dog feel hungry and causes an excessive appetite. People who have dogs with Cushing’s disease often will complain that the dog is absolutely ravenous all the time, not only scarfing up dog food but also raiding the kitchen trashcan and counter-surfing. Again, not necessarily an abnormal finding in many dogs, but one to evaluate in conjunction with other observations.
In the early phases of the disease the owner will note the excessive appetite and weight gain, but left untreated this protein breakdown ultimately results in muscle breakdown as well.
Pot-bellied appearance
Homer Simpson is not really an attractive cartoon character, and a gut like that doesn’t look good on dogs, either. I mentioned above that dogs with Cushing’s often have excessive weight gain, and this certainly contributes to their enlarged appearance.
In addition, Cushing’s causes liver enlargement, called “heptomegaly”. This results in a decidedly “pot-bellied” appearance, as the enlarged liver causes the abdomen to distend. Again, several diseases and conditions can cause hepatomegaly, but in Cushing’s patients the inciting cause is accumulation of the hormone glycogen in the tissues of the liver. The excessive cortisol production in the adrenal glands is once again the culprit.
An owner will notice the increased abdominal girth but a veterinarian can typically feel the liver enlargement with their hands on physical examination.
Skin changes
Cushing’s dogs often just look like a mess. Not only are they overweight, but they often have hair loss and skin diseases as well. One of the things that makes Cushing’s so rewarding to treat is that once the disease is under control, the dog just looks a lot better, and also feels better.
Hair loss with Cushing’s disease usually occurs along the top part of the body, and it’s usually symmetrical, meaning the loss pattern looks the same on both sides of the spine. The disease causes atrophy of the hair follicles, which causes the hair loss.
Cushing’s dogs are also prone to terrible skin infections because the excessive cortisol lowers the immune response, predisposing them to infections. Sometimes we’ll note blackhead-like lesions on the skin of the abdomen, called “comedones” as well.
Reproductive changes
This is not one we notice as commonly in the United States, since most adult dogs are spayed or neutered. But intact dogs with Cushing’s disease can undergo changes to their reproductive tracts causing enlargement of the organs (females) or atrophy (males). In females owners might also note that reproductive cycling does not occur normally.
As you can likely see, the signs of Cushing’s disease are similar to lots of other diseases. But as a pet parent being alert to these changes in your older dog can speed diagnosis and treatment of this potentially serious condition. Left untreated dogs with Cushing’s are predisposed to a number of internal problems, including high blood pressure, urinary tract infections, urinary stones, pancreatitis, clot formation/stroke, diabetes, and vision loss, so early diagnosis and control are important to preventing the majority of the serious complications of this disease.
Because the disease can be caused by either pituitary problems or adrenal gland problems, there’s not one “perfect” test for Cushing’s. 80-90% of dogs with Cushing’s typically have the pituitary form, so usually we start looking there. Treatment of the disease depends on which type the dog has, and with the pituitary form, because the tumor is almost always non-malignant, we typically treat with medications that slow production of cortisol.
If Cushing’s is caused by an adrenal tumor, the recommended treatment is typically surgical removal of the affected gland.