What is Addison’s disease?
The adrenal glands are found close to the kidneys
Hypoadrenocorticism (or Addison’s disease as it is more commonly known) is a disease where the body does not produce enough steroid hormone. Steroids in the body are primarily produced by the two adrenal glands which are found in the abdomen close to the left and right kidneys. The main steroid hormones produced by the body are called aldosterone and glucocorticoid.
Aldosterone is important in the maintenance of normal salt and water balance in the body. Glucocorticoids have widespread effects on the management of proteins and sugars by the body.
Glucocorticoid release from the adrenal glands is under the control of a substance produced in a gland in the brain called the pituitary gland. Aldosterone release is regulated by a hormone system and by blood potassium levels.
What causes Addison’s disease?
Addison’s disease is normally caused by destruction of tissue of the adrenal gland.
- In the majority of cases the destruction does not have an identifiable underlying cause (this is called ‘idiopathic disease’).
- In most cases the adrenal glands stop producing both aldosterone and glucocorticoid (known as ‘primary hypoadrenocorticism’).
- Occasionally, only glucocorticoids are lacking (known as ‘atypical hypoadrenocorticism’).
- Sometimes Addison’s disease occurs in combination with diseases of other glands such as hypothyroidism (this is a disease that causes thyroid hormone levels in the blood stream to be low).
Which animals are at greater risk of developing Addison’s disease?
Standard Poodle: one of a number of breeds predisposed to Addison’s disease
Addison’s disease is a rare disease in the dog; however, it probably occurs more often than is recognised. It is a very rare disease in the cat. Any breed of dog can be affected with Addison’s disease but a predisposition has been shown in Nova Scotia Duck Tolling Retrievers, Bearded Collies, Portugese water dogs and Standard Poodles. In addition Great Danes, Rottweilers, West Highland White Terriers and Soft Coated Wheaten Terriers appear to be at greater risk. Addison’s disease appears to be a disease of the young and middle-aged dog. Approximately 70% of dogs with naturally occurring Addison’s disease are female.
What are the signs of Addison’s disease?
Presenting signs in Addison’s disease vary from mild to severe and do not typically focus attention on any one major body system. The presentation of sudden onset Addison’s disease (the so called ‘Addisonian crisis’) is collapse and profound dullness. Some patients have a slow heart rate. Addison’s disease is easily confused with many other diseases. The presenting signs in longer standing disease are vague and may include vomiting, reduced appetite, tiredness, weight loss, diarrhoea, increased thirst and increased urination.
How is Addison’s disease diagnosed?
Blood tests can sometimes reveal characteristic changes in salt levels. Kidney numbers can also be elevated and mild anaemia (low red blood cells) is not uncommon. The salt changes occur as a result of a deficiency of aldosterone and subsequent effects on the way the kidney normally handles these salts. The salt changes, specifically a high blood potassium level, can have serious effects on the heart.
Blood samples are taken for the ‘ACTH Stimulation test’
A definite diagnosis of Addison’s disease is made by your veterinary surgeon performing an ACTH stimulation test on your dog’s blood. This is a test where blood is taken, a drug (ACTH) is given to try and stimulate the adrenal gland and then a second blood test is taken one hour later. If the adrenal gland fails to respond to the drug, Addison’s disease is diagnosed.
What is the treatment for Addison’s disease?
Prednisolone and fludrocortisone are tablet medications used to manage patients with Addison’s disease. Most dogs only need fludrocortisone longer term
The immediate treatment of life-threatening Addison’s disease involves the careful administration of fluids (‘a drip’) into the blood stream. Steroids are replaced by injection into the vein. Once animals are stable they are gradually moved onto tablet medication. Most animals with Addison’s disease will be discharged with prednisolone and fludrocortisone. Long term, the majority of animals can be managed with fludrocortisone alone and this drug is given once or twice daily. The fludrocortisone dose often needs to be increased with time. In times of stress or illness (veterinary visits, bonfire night, boarding etc) animals will often need a dose of prednisolone in addition to their fludrocortisone and your veterinary surgeon will advise you on what to do in these situations.
Side effects of fludrocortisone can include increased drinking, increased urination, panting and muscle wastage. Occasionally a monthly injectable medication (deoxycortisone pivalate) is used in place of fludrocortisone, although if this is the case animals need to be continued on prednisolone or another glucocorticoid medication called cortisone acetate. Deoxycortisone pivalate is not readily available in the UK or Europe.
What is the outlook for dogs with Addison’s disease?
Once animals are on appropriate therapy, they will require regular veterinary appointments for re-assessment and monitoring. The outlook for many dogs with Addison’s disease is very good with appropriate monitoring and treatment.