Cushings and Addisons Diseases are both hormonal problems of the adrenal gland. Cushing’s is caused by an overactive gland and is very common, especially in middle to old age dogs. Cushing’s disease is more correctly called Hyperadrenocorticism and this reflects the overproduction of the hormone Cortisol.
The adrenal gland is located close to the kidneys but is under close control from the pituitary gland in the brain. Most cases of Cushing’s are caused by a benign or a non-malignant tumour in the pituitary gland telling the adrenal gland to overproduce its hormones. Rarely Cushing’s can be due to a tumour on one of the adrenal glands, again this can be benign or malignant.
The most common symptom owners notice is an increased thirst and often dogs will start to ask to go out in the night. They can also become really hungry and start scavenging or raiding the rubbish bin. Other symptoms include; hair loss, lethargy, skin changes and a potbellied appearance.
In a normal dog short bursts of Cortisol help with the fight or flight response in times of stress. But if the level of Cortisol is constantly raised (as in Cushing’s) it has a detrimental effect on the dog’s health as the body is constantly in a state of stress.
If we are suspicious of Cushing’s, we will screen for it with a blood and urine test. We are looking for raised liver enzymes and dilute urine. We can then perform a more specific test called an ACTH stimulation test and, in most cases, this will give us a definitive diagnosis although sometimes even this can be inconclusive.
We treat most cases of Cushing’s with a daily tablet called Vetoryl which reduces the production of hormone by the adrenal gland. It is important to realise this is a treatment not a cure, so medication is lifelong and regular blood tests are required for monitoring the dosage.
Addison’s Disease or Hypoadrenocorticism is an underactive adrenal gland so there is a lack of hormone production. It is most commonly due to an autoimmune disease - when the body’s own immune system attacks the adrenal gland. It has very vague symptoms from lethargy, weakness, vomiting, diarrhoea to an acute collapse known as Addisonian Crisis. Dogs that are presented in an Addisonian Crisis require immediate veterinary attention to give intravenous fluid therapy and drugs to stabilise electrolyte levels.
If Addison’s is suspected, we can look at blood tests and a high potassium and low sodium levels make Addison’s disease highly likely. We can confirm the diagnosis with an ACTH stimulation test-looking for opposite results to Cushing’s. Treatment is again lifelong and is a combination of a monthly injection to replace one set of hormones and a daily tablet to replace the steroid hormone.