Cushing’s Disease in Dogs
A few months back we got a case in our hospital with clinical signs of polyuria, polydipsia and inappetence in a dog of middle-age. This was the shelter dog, recently adopted by an altruistic family. The bundle of other reasons could cause the above clinical signs although we ultimately narrow down our diagnosis to Cushing’s disease after several other differential diagnoses came negative. Let’s understand this disease briefly:
What is Cushing’s disease?
It is a condition caused by overproduction of cortisol hormone. It is very common in middle aged and older dogs.
Why does it happen?
We have some ductless glands in our body. They are like manufacturing units of chemical messengers called hormones and blood distribute it throughout the body. In a healthy body it produces these hormones in a balanced amount. Any disturbance in an equilibrium of these chemical messengers can muddle the functions of the organ they supervise and result in illness or disorders.
Cushing occurs through one such imbalance in cortisol hormone. This cortisol hormone released by a triangular shaped adrenal gland over kidney. Adrenal glands exchange message to produce cortisol by the pituitary gland located on the base of the brain. Any tumorous growth or chronic stress can disturb the normal production of the cortisol hormone results into several symptoms.
In most of the cases, the tumorous growth in the pituitary gland cause Cushing’s disease. Tumor of the adrenal gland is rare. We diagnose only fifteen percent dogs with this condition.
Some breeds are more prone to suffer from Cushing’s disease than others like -
- Yorkshire terrier
- German Shepherd
- Cocker spaniel
- Labrador retriever
What is the function of cortisol hormone?
Stress signals by body causes release of a cortisol hormone also known as the ‘stress hormone’. It releases in normal ‘flight and fright’ response which helps in survival of living beings. When a body of animal sense stress, the cortisol hormone released by adrenal glands reduces the glucose storage and inhibit insulin production, lumen of arteries gets narrow and together with epinephrine it increases heart rate.
Now, when we know the function of this hormone, let’s see the consequences and symptoms of it, when it is constantly elevated:
Consequences of high cortisol levels for a long time -
- Constant high level of cortisol, decrease in insulin and increase in a level of blood glucose.
- The cells in a body gets starved as they cannot use the elevated blood glucose because of a low insulin level which causes false hunger signals. Animals will eat more and there is extra glucose in blood which will store in the form of fat in the body result into weight gain.
- There will be an increase in the heart rate and blood pressure which leads to damage of the arteries and can even lead to heart attack or stroke.
- Hair loss
- Lack of energy, lethargic and depressed.
There are three crucial tests that veterinarians prefer to do for a confirmation of Cushing’s disease:
- ACTH Stimulation Test – It is a very popular test for the diagnosis of the Cushing’s disease but we use it for hypofunction and not hyperfunction of the adrenal gland. Sometimes, this test cannot catch positive animals with this disorder, around 20-30% pituitary abnormality and 50% of the adrenal tumor. Consider this test only when an animal is showing clinical signs. It helps to determine the release of cortisol from adrenal glands in response to ACTH injection.
- A. Low dose of dexamethasone suppression test (LDDS) – We use it for Hyperadrenocortisism. In this we administer a man-made synthetic cortisol for example dexamethasone. The pituitary gland secretes ACTH which stimulates the adrenal gland to produce cortisol in response to any stress. When level of a cortisol increase in blood, it signals to the pituitary to lower or cut down production of ACTH but in case of Cushing’s Syndrome this negative feedback loop do not work properly in controlling level of cortisol as per need of body. This test exploits troubled negative feedback mechanism to diagnose Cushing’s disease.
B. High dose dexamethasone suppression test (HDDS) — In confirmed case of this disease when a low dose test couldn’t differentiate the type of Cushing’s disease, we use HDDS test.
* If cortisol levels decreases during 4-8 hours intervals after a high dose of dexamethasone, it indicates pituitary origin of disease.
* When levels do not reduce from the preinjection sample, the diagnosis is the adrenal origin of Cushing’s disease.
Urine Cortisol/Creatinine ratio:
In Cushing’s disease the Cortisol and Creatinine ratio gets elevated. This can also increase because of stress. So, we should not take it as a final diagnosis.
Before performing the above tests, a Veterinarian will do an initial screening to evaluate the following parameters:
- Complete Blood Count
- Serum Biochemistry (protein, lipids, alkaline phosphatase, glucose and metabolites)
- Urinalysis (specific gravity, cell culture and glucose). Cystitis occurs because of an increased level of cortisol which suppresses immunity system in dogs with Cushing’s disease and develops bacterial infection especially bladder infection.
- X-rays and Ultrasonography- to check adrenal glands and liver.
Focus of treatment in Cushing’s is generally to reduce clinical signs and to improve the quality of life of a patient.
Treatment is only indicated for patients showing any symptoms of disease. We do not recommend any treatment when clinical signs are absent and the test is positive.
Treatment protocol varies with the type of Hyperadrenocortisism.
- Oral medication– Life long medication like trilostane is prescribed to manage the pituitary type of Cushing’s disease. The medicine is induced once or twice weekly for life.
- Radiation- It shrinks the pituitary tumor, particularly helpful in small tumors of pituitary.
- Surgery – In adrenal dependent Cushing’s disease, we excise the affected adrenal gland but if a tumor is malignant, we do not remove it to prevent its spread to other organs. Oral medication helps to reduce the hormone level before surgery. Trans Sphenoidal surgery is done for pituitary gland tumor.
Chances of recovery are generally good if treatment is provided. It may take weeks to months for complete recovery of the appetite, water intake and fur. After tumor excision hormonal imbalance and symptoms related to it alleviates.
Just keep in mind that treatment for one type of Cushing’s disease cannot treat the other type.
This disease needs a life long treatment and regular monitoring, which is compulsory as your veterinarian needs to keep screening your pet’s general health, side effects of medication and hormonal levels after giving treatment. It requires a lot of dedication, love and punctuality to keep your fur baby in a healthy state. But, as we know every cloud has its silver lining so as the prognosis of this disease which is good even if, it seems to be difficult. It can get better with proper treatment and regular checkups by your veterinarian. All you need is, to be regular with the treatment protocol and vet’s visit.