Hyperadrenocorticism, otherwise known as Cushing’s disease, is caused by an overproduction of the hormone cortisol. Cortisol is produced by the adrenal glands, and is stimulated to do so by hormones produced by the pituitary gland.
Cushing’s may be due to one of three things:
- an adrenal tumour which produces cortisol independently of the pituitary gland
- a pituitary gland tumour which overstimulates the adrenals
- due to the excessive administration of corticosteroids (iatrogenic).
The pituitary dependent form (PDH) is the most common form of the disease making up approximately 80% of cases. The large majority of pituitary tumours are benign and if small are unlikely to invade or press on other areas in the brain. Adrenal tumours can be benign or malignant and usually affects only one adrenal gland.
The condition mostly affects middle-aged and older dogs but has been documented in dogs as young as 1yr of age. Breeds commonly affected include Dachshunds, all Poodle breeds, Terriers, German Shepherds, Beagles, Labradors and Boxers although PDH seems to occur more frequently in small breed dogs. It is uncommon in cats and when seen is most often associated with diabetes mellitus.
There are many signs of Cushing’s disease and not all are present in every case. Some of the symptoms that can be seen are:
- An increase in thirst and water intake
- An increase in appetite
- Weight gain
- Lethargy or exercise intolerance
- Changes to the skin and coat (e.g. symmetrical hair loss over the trunk)
- Panting
- Abdominal enlargement
- Weakness, muscle wasting
Diagnosing Cushing’s disease can be tricky. It can sometimes require several different blood tests, a urinalysis and occasionally abdominal imaging to inspect the liver, kidneys and adrenal glands. Once a diagnosis is confirmed it is important to also rule out other abnormalities such as secondary infections (skin and urinary tract are the common areas) and diabetes.
The good news is that once a diagnosis of Cushing’s is confirmed, treatment can be commenced to control the disease. Daily medications are the most common form of treatment and when given appropriately can reduce a dog’s symptoms and greatly improve their quality of life. Ongoing monitoring in the form of regular blood and urine testing is essential.
For the more serious cases caused by malignant adrenal tumours, adrenalectomy (removing the adrenal gland) can be curative. Radiation therapy can also be helpful in dogs with large pituitary-based tumours.