A few months back we got a case in our hospital with clinical signs of polyuria, polydipsia, and inappetence in dogs of middle-age. This was the shelter dog who was recently adopted by a kind family. Although the above-mentioned clinical signs could be caused by a bundle of other reasons we ultimately narrow down our diagnosis to Cushing’s disease after several other differential diagnoses came negative. Let's understand this disease in brief:
What is Cushing’s disease?
It is a condition caused by the overproduction of the cortisol hormone. It is very common in middle-aged and older dogs.
Why does it happen?
We have some ductless glands in our body which are like manufacturing units of chemical messengers called hormones that are distributed by the blood throughout the body. In a healthy body, these hormones are produced in balanced in the equilibrium of these chemical messengers can muddle the functions of the organ they supervise and results in illness or disorders.
Cushing occurs through one such imbalance in the cortisol hormone. This cortisol hormone is released by the triangular-shaped adrenal gland present all over the kidney. Adrenal glands exchange messages 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 in a number of symptoms.
In the majority of cases, the tumorous growth in the pituitary causes Cushing’s disease. Tumor of the adrenal gland is less common only fifteen percent of dogs are diagnosed with this type.
Susceptible breeds-
Some breeds are more prone to suffer from Cushing’s disease than others like-
§ Poodle
§ Dachshund
§ Yorkshire terrier
§ German Shepherd
§ Boxer
§ Cocker spaniel
§ Labrador retriever
What is the function of the cortisol hormone?
Cortisol hormone is released in response to stress signals in the body and because of this reason, it is called the stress hormone. It is released in a normal ‘flight and fright’ response which helps in the survival of living beings. When a body of an animal sense stress, the cortisol hormone is released by adrenal glands which in turn reduces the glucose storage and inhibits insulin production, a lumen of arteries gets narrow and together with epinephrin, it increases heart rate.
Now when we know the function of this hormone let's see the consequences and symptoms it, when it is present at a constantly high level.
Consequences of high cortisol levels for a long time-
1. Constant high level of cortisol, low level of insulin, and high level of blood glucose.
2. As glucose increase in blood, the cells in the body get starved as they are not able to utilize this glucose because of low insulin level which causes false hunger signals. Animals will eat more and there is extra glucose in the blood which will store in the form of fat in the body result in weight gain.
3. There will be an increase in the heart rate and blood pressure which leads to damage of arteries and can even lead to heart attack or stroke.
Symptoms:-
1 polydypsia
2 Polyphagia
3 panting
4 hair loss
5 lack of energy, lethargic, dull, and depressed.
Diagnosis
There are three main tests that veterinarians prefer to do for a confirmed diagnosis of Cushing's disease :
1. ACTH Stimulation Test – It is a very popular test for the diagnosis of Cushing's disease but it is generally used for hypofunction of adrenal and not hyperfunction of the adrenal gland. Sometimes, this test fails to catch positive animals with this disorder, around 20-30 % pituitary abnormality and 50% of adrenal tumors. Only use this test when the animal is showing clinical signs. This test helps to determine the release of cortisol from adrenal glands in response to ACTH injection.
2. A. Low dose of dexamethasone suppression test ( LDDST) – It is used for hyperadrenocorticism In this, the man-made synthetic cortisol i.e dexamethasone is given. ACTH is secreted by the pituitary gland and it stimulates the adrenal to produce cortisol in response to any stress. When the level of cortisol increase in the blood it sends signals to the pituitary to lower or cut down the production of ACTH but in the case of Cushing’s Syndrome this negative feedback loop does not work properly results in trouble controlling the level of cortisol as per the need of a body. This test exploit** troubled negative feedback mechanism to diagnose Cushing’s disease.
B. High-dose dexamethasone suppression test (HDDST) — In the confirmed case of Cushing’s disease when the low-dose test couldn’t able to differentiate the type of Cushing’s, we use the HDDS test.
* If cortisol level decrease during 4-8 hours interval of giving a high dose of dexamethasone this indicates pituitary origin.
* If levels do not come to reduce from the preinjection sample the diagnosis is the adrenal origin of Cushing’s.
3. Urine Cortisol/ Creatinine ratio:-
In Cushing’s disease, the Cortisol and creatinine ratio elevated. This can also increase due to stress. So, we should not take it as a confirmative diagnosis.
The above tests are extensive tests for Cushing’s disease. Before performing these tests, initial screening is done in which veterinarian perform-
- · Complete Blood Count
- · Serum Biochemistry (protein, lipids, alkaline phosphatase, glucose, and metabolites)
- · Urinalysis ( specific gravity, cell culture, and glucose). Cystitis occurs due to high levels of cortisol which suppresses the immunity system in dogs with Cushing’s and develops bacterial infection, especially bladder infection.
- · Xrays and Ultrasonography- to check adrenal glands and liver.
Treatment-
The focus of treatment in Cushing’s is generally to reduce clinical signs and to improve the quality of life of the patient.
Treatment should be given only to patients showing any symptoms of this disease.
If clinical signs are absent and the test is positive treatment is not indicated.
Treatment protocol varies with the type of Hyperadrenocorticism*.
- v Oral – Life-long medication like trilostane is prescribed to manage the pituitary type of Cushing’s disease. Induction is done once or twice weekly for life.
- v Radiation- Is given to shrink the pituitary tumor. It is particularly helpful in small tumors of the pituitary.
- v Surgery – In adrenal dependent, Cushing’s disease the affected adrenal gland is excised but if it is malignant then it is not removed to prevent its spread to other organs. Oral medication is given to reduce the hormone level before surgery.
- o Trans Sphenoidal surgery is done for pituitary gland tumors.
Prognosis-
Chances of recovery are generally good if treatment is given. It may take weeks to months to completely recover the appetite, water intake, and fur. After tumor excision hormonal imbalance and symptoms related to it alleviate.
Just keep in mind that treatment for one type of Cushing’s disease cannot treat the other type.
Conclusion-
This disease needs lifelong treatment and regular monitoring, which is compulsory as your veterinarian need to keep screening your pet’s general health, side effects of medication, and hormonal level 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
the prognosis of this disease is generally 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.
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