What is it?
Addison's disease, also known as hypoadrenocorticism, is a very serious hormone imbalance. Affected dogs often have only very subtle, intermittent signs, until the disease progresses to a life-threatening Addisonian Crisis.
What causes it?
Lack of natural steroid hormones, made in the dog's adrenal glands. Normally, dogs make two types of steroids: glucocorticoids (like cortisol, which help them cope with stress) and mineralocorticoids (which control their salt and water balance). In Addison's, the adrenal glands do not produce enough of these hormones; this may be because of damage to the adrenal glands (Primary Addison's) or, more rarely, injury or disease of other glands in the body that regulate the action of the adrenals, such as the pituitary (or "Master") gland. Occasionally, Addison's can also be the result of excessive steroid medications (we call this "Iatrogenic Addison's", and it occurs because the adrenal glands stop making steroids because we are giving the dog so many; if we reduce the dose too fast, the glands cannot adapt in time).
What dogs are at risk?
Addison's disease can affect any dog. However, it is most common in young to middle-aged bitches, and is slightly less common in male dogs of all ages.
What are the symptoms?
Much of the time, a dog with Addison's may appear almost normal. However, observant owners will often notice subtle signs such as intermittent vomiting, shaking, muscle weakness or weight loss. These symptoms come and go, and in between episodes may disappear completely. Eventually, however, an affected dog will undergo an Addisonian Crisis, where the symptoms suddenly and dramatically worsen. This is a life-threatening condition, and is usually characterised by acute, severe vomiting and diarrhoea, dehydration, collapse and the rapid onset of shock. Without treatment, it is often fatal. Sadly, in as many as 30% of dogs, the first symptom is an Addisonian Crisis.
How is it diagnosed?
There are characteristic changes in the blood salts that are very suggestive of Addison's (especially the ratio between the sodium and potassium). A conclusive diagnosis, however, requires a specialist blood test called and ACTH stimulation test, where a sample of blood is taken, and then your dog is injected with a hormone that should increase the production of cortisol. A second blood sample is then drawn some time later, and if the dog's cortisol level hasn't risen, they are confirmed to have Addison's disease.
How can it be treated or managed?
Fortunately, once diagnosed, it is perfectly possible to treat Addison's very effectively. In a Crisis, we would put the dog on a drip to correct the salt and fluid imbalances, and give them a steroid injection to help tide them over. Then we would aim to replace the "missing" hormones with specialist steroid medication - either as tablets or a long-acting injection. Regular monitoring is important to ensure that we're giving them the right amount of artificial steroids, but this can normally be done with a simple one-off blood test.
Can it be prevented?
Unfortunately, neither Primary nor Secondary Addison's can be prevented as yet. However, Iatrogenic Addison's can be avoided by only very, very gradually reducing the dose of steroids if your dog has to be on these medications for any reason.