Cushing’s disease is one of the most common hormonal diseases in dogs. Also called hypercortisolism, it is due to an abnormally high production of cortisol by the body.
It usually affects dogs 8 years of age and older. All breeds are susceptible to being affected, but certain breeds are predisposed: poodles, dachshunds, boxers, terriers.
Causes of Cushing’s disease in dogs
Cortisol is a hormone produced by small glands located above the kidneys, the adrenal glands. Cortisol is similar to cortisone in terms of effects, cortisone being a synthetic molecule while cortisol is produced naturally by the body. Small amounts are needed in any organism for hormonal balance, but large and prolonged doses are harmful.
The production of cortisol by the adrenal glands takes place under the control of a small gland located in the brain: the pituitary gland. This controls the production of cortisol in the adrenals by another hormone: ACTH.
Thus, Cushing’s disease can have two mechanisms of action:
- Either the pituitary gland is out of order and commands the adrenals to produce abnormally high cortisol. This is the majority of cases. About 85% of Cushing’s diseases are of pituitary origin. Usually, this is due to a small benign tumor in the pituitary gland, producing excess ACTH.
- Either the pituitary is functioning properly, but it’s the adrenal glands that get carried away and produce too much cortisol. This is the case in about 15% of Cushing’s disease and is usually caused by a benign or malignant tumor of one of the two adrenal glands.
Cushing’s disease can also be caused by repeated and prolonged administration of corticosteroid drugs. This can be the case, for example, in dogs with chronic itching. In this case, stopping these treatments generally allows a return to normal.
Symptoms of Cushing’s disease in dogs
The main symptoms of Cushing’s disease are:
- An increase in the amount of water drunk (polydipsia)
- An increase in the amount of urine passed (polyuria)
- Increased appetite
- Hair loss: this is often quite characteristic because it is bilateral and symmetrical. It mainly affects the flanks and the back.
- Distension of the abdomen
- Muscle wasting
- A decline in shape, even apathy
- In some cases, liver failure may be present
The productions of the different hormones of an organism being very linked to each other, the imbalance of one of them can lead to the disruption of another. Thus, diabetes can be associated with hyperadrenocorticism. In females, a modification of the hormonal cycle, or even an absence of heat, can also be observed.
The symptoms are often quite suggestive. Your veterinarian may therefore suspect Cushing’s disease during the clinical examination. However, additional examinations are necessary to confirm and detail the diagnosis.
A specific test makes it possible to confirm a suspicion of Cushing’s disease: the ACTH stimulation test. This involves taking blood samples from the animal, before and after administration of ACTH, to measure the blood cortisol and see how the adrenal glands react.
Also, like any hormonal disease, Cushing’s disease can affect other organs. It may therefore be advisable to do an additional assessment, in particular to look for possible hepatic or pancreatic complications.
Once the diagnosis of Cushing’s disease has been confirmed, other additional examinations may be recommended to specify the cause (pituitary or adrenal): dexamethasone braking test, ultrasound, CT scan or even MRI.
Treatment and prognosis
The treatment offered usually depends on the cause of the disease.
In the majority of cases, the origin is pituitary. The treatment will then be most often drug. There is a specific treatment, making it possible to decrease the production of cortisol by the adrenal glands: trilostane. The dosage to be administered may vary from dog to dog. At the start of treatment, blood checks with stimulation tests should be carried out in order to readjust the dose. This treatment must be carried out for life. In rare cases, treatment to eradicate the pituitary tumor may be offered.
Other drug treatments can also be used, depending on the situation.
When Cushing’s disease is due to a tumor in one of the adrenal glands, surgical excision of the latter is recommended, and may allow the dog to be cured permanently.
Your veterinarian will discuss with you the best options for your pet.
In all cases, the prognosis is generally good with regular monitoring.
Monitoring of Cushing’s disease in dogs
Once the condition of the animal has stabilized, monitoring is relatively light. This is to check that the drug treatment is still effective, and possibly readjust the dose if necessary. This follow-up will be necessary for life.
However, it is important to remain vigilant for a possible relapse of symptoms, even if your dog is under treatment, and to contact your veterinarian if necessary.