Cushing's Disease is defined as the over-production of a stress hormone called cortisol. Cortisol doesn’t just help a dog to react to danger; it is vital to her mood, motivation and metabolism and has a part to play in the maintenance of her immunity.
Cortisol is made by the adrenal glands. These are two glands which sit just in front of a dog’s kidneys. In a normal dog the adrenal glands are stimulated to produce cortisol by messages sent from the pituitary gland which sits at the base of the brain.
An overproduction of cortisol is caused by one of two means: an abnormal message from the pituitary gland or abnormality of the adrenal glands.
A problem faced by vets in their diagnosis of Cushing’s Disease is that of being sure of its symptoms. The illness manifests in various ways but most of the symptoms associated with it are those which the dog may exhibit if she is simply lacking in energy or over-eating.
To complicate things still further, Cushing’s Disease is seen of dogs in the middle to late years that often put on weight and exercise less.
How does Cushing’s Disease affect dogs?
Irrespective of whether the over-production of cortisol is caused by the pituitary or adrenal glands, the symptoms of Cushing’s Disease are more or less the same.
Only blood screening and further examination of the canine patient is able to identify the root cause.
Symptoms of the disease will be one or more of the following:
- Chronic skin infections
- Darkening of the skin
- Bladder infections
- Increased appetite and thirst
- Muscular atrophy (wasting away of muscle)
- Excessive panting
Dogs with Cushing's may also have a pot-belly, due to the build up of fatty deposits.
The main causes of Cushing’s Disease in dogs
Let us look more closely at the two main causes of canine Cushing’s Disease.
1. A tumour of the pituitary gland
90% of all instances of Cushing’s Disease are due to a pituitary tumour. The tumour forces the pituitary gland to excessively secrete ACTH (adrenocorticotropic hormone), which stimulates the adrenal glands’ release of cortisol.
Both types of Cushing’s Disease can be treated successfully (more on this later) but if the pituitary tumour enlarges the dog’s prognosis, this is not good because the tumour begins to affect her neurological health.
2. A tumour of the adrenal glands
A tumour of the adrenal glands naturally causes hormonal output to be awry. This type of tumour is less rare, and if it can be determined that the tumour is benign then surgery is recommended for your dog.
If the tumour is either malignant or metastatic or both, the outlook is less favourable even after surgery.
What are the best treatments of Cushing’s Disease in dogs?
To identify the type of Cushing’s disease leads your vet to make appropriate recommendations of the course of treatment.
Oral or injected medications prove effective in the management (but not the cure) of the disease. Surgery is usually only an option if it is deemed necessary for the animal’s survival.
Treatment of the tumour of the pituitary gland
In the event of a diagnosis of a benign pituitary tumour your dog may be given a medication called Vetoryl (trilostane). This drug ceases the adrenal production of cortisol and is used in both types of Cushing’s Disease.
The human chemotherapy drug Lysodren (mitotane) has also been used to treat Cushingoid dogs. Lysodren targets the parts of the adrenal gland that produce cortisol. Lysodren is known to have serious side effects.
Surgical removal of a tumour of the pituitary gland can be considered in rare cases but the procedure usually poses too much of a risk to the health of the dog.
Non-surgical treatments may not be necessary for dogs with mild symptoms; your vet may want to closely monitor your pet for a while first.
Treatment of the tumour of the adrenal gland
If a tumour of the adrenal gland is deemed to be operative your vet may refer your dog for surgery. However, benign tumours are more easily treated with medications to shrink them.
Malignant adrenal tumours may be removed if it is decided that your dog’s chances of recovery are good. If surgery is not possible or the malignancy has spread to other parts of the body the prognosis is bleak.
Iatrogenic Cushing’s Disease
This is a condition that has all the hallmarks of adrenal and pituitary Cushing’s Disease. It is caused by the application or ingestion of glucocorticoids over a prolonged period of time (roughly nine months or more).
Glucocorticoids are the active ingredient of steroid medicines designed to treat ailments such as asthma, autoimmune diseases and inflammation. Treatment of iatrogenic Cushing’s Disease involves the stopping of steroidal applications.
Prognosis and summary
Although prescription medicines can treat the hormonal imbalance of the dog they do not cure the problem. Only the removal of the affected gland cures Cushing’s Disease. However, medication (taken in exact accordance with the vet’s instructions) adequately manages the disease over many years.
A dog with Cushing’s Disease requires a good deal of support and looking after. You should visit your vet regularly and closely monitor the health of your dog.