Cushing’s Disease in Dogs
Cushing’s disease (Hyperadrenocorticism) is caused by excess cortisol hormones produced by the the adrenal glands. The adrenal glands are located near the kidneys and produce important hormones that regulate body functions. One such hormone is cortisol which is released in times of stress to prepare for a fight or flight situation. It is involved in the metabolism of fat and sugars. It also helps to regulate salt and water in and out of the body.
In Cushing’s disease, the body is exposed to cortisol most of the time instead of during periods of stress. This results in debilitating effects.
Causes of Cushing’s disease
There are 3 main causes of Cushing’s disease. They all result in similar symptoms. However, the prognosis varies for each form.
- Pituitary gland tumour-This is the most common cause of Cushing’s disease. 85% of cases are due to an pituitary gland tumour. Majority of these tumours are benign resulting in overproduction of a hormone that causes the adrenal gland to produce cortisol. If the tumour is large it can also cause neurological symptoms. Prognosis of the dog depends on the rate of growth of the tumour. The activity of the gland is often well-controlled with medication.
- Adrenal gland tumour-In 15% of dogs with Cushing’s disease, a tumour in the adrenal gland results in overproduction of cortisol directly. The tumour may be malignant and invade into neighbouring structures. Surgery is indicated to remove the tumour if there is no evidence of spread.
- Iatrogenic-This is caused by excessive administration of oral or injectable steroid medications. Steroids are commonly used to relieve inflammation and itchiness for skin conditions. Relief is usually rapid and many owners request injections or steroid pills repeatedly to achieve the desired effect. As a result of high steroid levels in the body, the adrenal glands start to waste away and are unable to release cortisol on its own. Effects of steroids can persists in the body for up to 3 months. To allow the adrenal glands to recover, the steroids are gradually tapered. It is not recommended to discontinue oral steroids suddenly.
Symptoms of Cushing’s disease
Increase in thirst- Increase in appetite
- Increase in urination
- Increase panting
- Pot-bellied appearance
- Chronic skin disease
- Lethargy
- Thinning of skin
Diagnosis of Cushing’s disease
An initial database is collected from suspected patients. This includes a complete blood count, chemistry panel and a urinalysis. Elevated alkaline phosphatase (ALKP) and cholesterol is commonly elevated in affected dogs. Urine tests done commonly reflect diluted urine and studies done show that 20% of dogs with Cushing’s disease have a bladder infection.
Two common tests that detect Cushing’s disease are the low-dose dexamethasone suppression (LDDS) test and the ACTH stimulation test.
An abdominal ultrasound can be carried out to diagnose adrenal tumours.
While the tests done can be very expensive, it enables us to determine the cause of the Cushing’s disease and which treatment is best for your pet.
Treatment
Pituitary tumour– Treatment involves administration of trilostane. Trilostane works by reducing the production of cortisol levels. As the drug is imported and therapy is usually lifelong, treatment can be costly. Although the tumour is not removed, the condition can be well controlled if the tumour remains small. In cases where the tumour grows rapidly, neurological symptoms develop worsening the prognosis
Adrenal Tumour– Treatment requires surgery where the adrenal tumour has to be removed. Often the tumour lies close to major blood vessels. Surgery is complicated and there are significant post-operative complications that may occur. If surgery is not possible, the tumour is managed with trilostane as above.
Iatrogenic– Treatment requires gradual tapering of steroids administered. This often results in recurrence of disease that was being controlled by the steroids.
Prognosis
As discussed, prognosis depends on the actual cause of Cushing’s disease and the size and type (benign or malignant) of tumour, if present. Patients that are on trilostane will need to be monitored with blood test and check ups to ensure that they are receiving the proper dosage.