Causes Of Cushing’s Disease In Dogs
There are three main causes of Cushing’s disease in dogs. Each of these causes requires a different type of treatment approach.
If your dog has allergies or another chronic condition, it is possible that this condition requires the constant administration of a treatment involving glucocorticoids. This can cause iatrogenic hyperadrenocorticism, by producing an excess of corticosteroids that flood your dog’s body. This is a reaction almost identical to that of an adrenal tumor, since adrenal tumors also have a similar effect on your dog’s body.
Even though the pituitary gland will attempt to cut secretion of ACTH, and the adrenal glands will attempt to stop producing so much cortisol, symptoms of Cushing’s disease eventually develop if the glucocorticoid treatment is not stopped. If your dog is being affected by this cause of Cushing’s disease, the adrenal glands of your dog will be shriveled, small, and atrophied.
Luckily, this is the most treatable type of Cushing’s disease, since the glucocorticoid treatment is gradually withdrawn, and the symptoms of Cushing’s disease eventually vanish.
Pituitary Dependent Hyperadrenocorticism
This is the most common cause of Cushing’s disease in dogs. Pituitary dependent hyperadrenocorticism accounts for roughly 85% of all instances of Cushing’s disease in dogs. Pituitary dependent Cushing’s disease involves an excess secretion of the hormone ACTH by the pituitary gland.
ACTH is what stimulates the adrenal glands to produce more cortisol and other glucocorticoids. With this cause, a microadenoma (benign, microscopic tumor) usually forms in the pituitary gland. This tumor outputs excessive amounts of ACTH, which causes the adrenal glands to produce large amounts of cortisol.
Normally, with elevated cortisol levels, the pituitary gland would then stop producing ACTH to halt the production of cortisol. However, in pituitary dependent hyperadrenocorticism, the pituitary gland is unable to respond to the elevated cortisol levels. The adrenal glands of a dog with Cushing’s disease caused by a pituitary gland tumor will usually be abnormally large, since they are working hard to produce high levels of cortisol in response to the ACTH.
In about 10-15% of instances of Cushing’s disease in dogs, the cause of the hyperadrenocorticism is related to the adrenal gland. An adrenal tumor develops, usually on one of the two adrenal glands. This tumor continues producing cortisol, even if the ACTH hormone levels secreted by the pituitary gland drop. An ultrasound of a dog experiencing adrenal-based hyperadrenocorticism will show that one adrenal gland is usually abnormally shaped or extremely large in comparison to the other adrenal gland.
Symptoms Of Cushing’s Disease In Dogs
Increased Water Consumption And Urination
This is a symptom that is present in about 80-85% of all dogs affected by Cushing’s disease. Many dogs with Cushing’s disease will drink anywhere from two to ten times the amount of water that they drink normally. As this will also result in increased urination, this may cause some dogs to lose control of their bladder functions indoors. Since this is also a condition that is common in aging dogs, many people do not see cause for alarm until their dog’s water consumption becomes severely evident.
This is another visible symptom of Cushing’s disease that usually provokes a dog’s owner to seek veterinary advice. However, hair loss is also a symptom of aging in older dogs, so it may go unnoticed as a symptom of Cushing’s disease for quite some time. Usually the hair loss is evenly distributed over both sides of the dog, and does not characteristically result in “clumps” of bare skin.
This has been identified as a symptom exhibited by dogs with Cushing’s disease, but again, it is not a definitive symptom for a positive diagnosis. Also, due to the nature of most dogs to pant, heavy panting may go unnoticed by dog owners.
Thinning Of The Skin
Many older dogs also experience thinning, or “papering” of the skin as they age, so this symptom of Cushing’s disease may also be hard to detect. Usually, thinning of the skin is accompanied by excessive hair loss, which is a much more visible symptom.
Increase In Appetite
Many dogs with Cushing’s disease seem to have an insatiable appetite, and may exhibit previously unapparent bad behavior in order to consume more food (such as eating garbage, stealing food, etc). This excessive eating also may contribute to significant weight gain.
While abdominal distention is a visible symptom of Cushing’s disease, it actually occurs because the muscle strength of your dog is weakening. Abdominal enlargement is also present because, in a dog with Cushing’s disease, fat may be redistributed from other storage areas to the abdomen. Also, in dogs with Cushing’s disease, the liver tends to become enlarged due to the excess cortisol secreted by the adrenal glands. This “potbelly” is usually very prominent in a dog with advanced Cushing’s, and is a serious enough symptom so that a dog exhibiting this symptom should be taken to a veterinary hospital immediately.
Weakening Of The Heart And Muscles
The weakening of a dog’s muscles because of Cushing’s disease may be present in behaviors such as lethargy, depression, and lack of interest in normal activities. Also, a dog with Cushing’s disease may wobble while walking, or seem hardly able to carry their own weight.
Calcinosis cutis is a symptom of Cushing’s disease that manifests in the form of mineralized skin nodules, also called “calcified skin lumps”. This symptom is not exhibited by all dogs, though it is said to be a textbook sign of Cushing’s diseas