Cushing's Disease in Dogs

Cushing's Disease 101

Cushing's disease in dogs, scientifically referred to as Hyperadrenocorticism, is caused by a disruption in the brain's normal communication process.

The hypothalmus is the part of the brain that directs the pituitary gland to produce and distribute the adrenocorticotrophic hormone (ACTH). ACTH in turn signals the adrenal glands to produce a secretion known as glucocorticoid, a substance that has lately used in the media under the layman's name of "cortisol".

Cortisol has been shown to help the body deal with the effects of stress, and it's presence has an affect on all the major organs and systems of your pet's body. Although the cortisol levels in the bloodstream are in a constant state of adjustment according to what the body needs at any given time, under normal circumstances they present no problem.

The trouble begins when more cortisol is produced than the body can utilize because cortisol suppresses the immune system. This can lead to a host of health problems including heart disease, liver failure, kidney failure, blood clots and infections.

Oddly enough, there is a benefit from all this excess cortisol for pets suffering from arthritis or dysplasia. The cortisol has an anti-inflammatory affect on tender joints, reducing pain and increasing mobility.

Causes of Cushing's Disease in Dogs

What causes excess cortisol production?

• Pituitary tumors can cause the gland to produce a constant flow of ACTH, forcing the adrenal glands to keep up cortisol production. This form of Cushings disease in dogs is known as Pituitary Dependent Hyperadrenocorticism, and can be somewhat detected by the enlarged state of the adrenals.
• Adrenal gland tumors can also be the source for the disruption in communication between the hypothalmus and the glandular systems, again resulting in the overproduction of cortisol. Adrenal based Cushing's may be suspected when there is a considerable size difference between the two adrenal glands.
• Giving external sources of glutocorticoid, such as steroids used to treat allergies, can artificially boost cortisol production, and sometimes leads to the onset of Cushing's symptoms. This medically induced form of Cushing's, referred to as Iatrogenic Hyperadrenocorticism, suppresses normal adrenal gland activity, causing the glands to become small and atrophied.

Outward Symptoms

Cushing's disease in dogs can be hard for owners to recognize because the symptoms are quite typical among aging pets and come on gradually. Perhaps the biggest clue would be finding more than one of these symptoms presenting at the same time, especially in a dog who would normally be considered middle aged.

Typical symptoms include:

• Increased appetite
• The appearance of a weight gain
• Constant thirst
• Increase in urination accidents
• General lethargy, slowing down
• Dull, thinning coat
• Lumps/tumors in the skin
• New dark pigmented areas on the skin, akin to liver spots
• Increased number of infections
• Seizures
• Onset of canine diabetes

Getting a Diagnosis

Diagnosing Cushing's disease in dogs is easier said than done because there is no single definitive test for the condition. As previously mentioned, a grouping of symptoms is usually the first clue, and X-rays revealing the current conditions of the pituitary and adrenal glands can also help diagnose the disease.

Additional veterinary testing might include:

• A dexamethasone suppression test, considered one of the best diagnostic tools for detecting Cushing's.
• A urine test, used to determine current cortisol/creatinine ratios.
• An ACTH stimulation test, used to determine a baseline reading before injecting ACTH, and recording the adrenal glands cortisol production response.

Treatment

Treatment is based on the type of Cushings diagnosed, and may include:

• Surgical removal of adrenal gland tumors, if possible.
• Chemotherapy and/or radiation treatments to shrink pituitary gland tumors.
• Gradual withdrawal of glutocorticoid medications, giving the adrenal glands time to recover and resume normal cortisol production.

In very advanced cases, euthanasia may be the kindest course of action.

Conclusion

Although Cushing's disease in dogs is treatable, it isn't always curable depending on it's exact cause, so the focus becomes making an affected pet as comfortable as possible. Great consideration should always be given to a dog's age and current health. In some cases, especially those where pets are known to have arthritic conditions, it may be safer and kinder on an elderly dog to leave the disease untreated rather than risk surgery or the unpleasant side effects of chemo.