What are adrenal hormones?
The adrenal glands live beside the kidneys. They are made up of a cortex (the outer layer) and the medulla (the middle). Both parts produce different hormones. Addison’s disease involves hormones produced by the cortex, called corticosteroids.
Corticosteroids help our bodies respond to stress. There are different types of corticosteroids: glucocorticoids and mineralocorticoids. Glucocorticoids (cortisol, prednisone, and dexamethasone) help our metabolism prepare for a “fight or flight” situation by burning rather than storing fuels. Mineralocorticoids (for example, aldosterone) are involved in sodium and potassium balance. Aldosterone tells the kidneys to retain sodium, which in turn pulls water from other tissues into the circulation. When sodium is kept, potassium is lost in the exchange. The retention of water maintains blood pressure and protects the body from dehydration or blood loss.
What is Addison’s Disease?
This is a deficiency (or lack) of corticosteroid hormones due to a destruction of the adrenal cortex. There are many possible causes for this but an autoimmune process is often the reason, or even certain medications could be attributed to the disease.
What are the symptoms of Addison’s Disease?
- Dogs are usually young (aged 4-5 years) but any age can be affected.
- In NZ we see a higher rate of Addison’s in Standard Poodles and Huntaways/Border Collies, but other breeds can get it.
- About 90% of the adrenal cortex isn’t functioning before clinical signs are seen.
- Early symptoms are vague: lethargy, with some dogs experiencing vomiting or diarrhoea. This can wax and wane and the dog can appear normal most of the time, but at times of stress they can get sicker. This can go on for some time.
- Addisonian crisis: this is when it all comes to a head and the dog collapses in shock. Collapse is due to the body’s inability to adapt to stress. Blood sugar drops, potassium levels rise and affect the heart. The heart rate slows and often develops arrythmias. Some of these animals may not survive.
Approximately 30% of dogs are diagnosed when they present in an Addisonian crisis.
Addison’s can mimic a lot of other disease processes. It is known as the “Great Imitator”. It can look like:
- Shock: treatment for this involves intravenous fluids and glucocorticoids. This happens to be the treatment for Addison’s as well, so the dog recovers well and often we don’t know why they collapsed in the first place.
- Kidney disease: Blood test results of a dog with Addison’s often show elevated BUN and creatinine, which are both elevated in animals with kidney failure. The difference is, that when treated with intravenous fluids, a dog with Addison’s will respond much more rapidly than a dog with renal failure.
- Low blood sugar: This can lead to seizures. We may suspect an insulin-secreting tumour in the pancreas.
- Recurring gastrointestinal disease: waxing/waning diarrhoea and/or vomiting with a poor appetite can suggest an inflammatory bowel condition.
- Megaoesophagus: This is when the oesophagus dilates due to a nerve dysfunction, causing pooling and regurgitation of undigested food. There are many causes of this, but Addison’s is one of them.
How do we diagnose Addison’s Disease?
Initially we will run full bloods including biochemistry, haematology and an electrolyte panel. There may be clues in these results, but remember that Addison’s imitates many other disease processes! If we suspect Addison’s we will include a cortisol level. This will help us rule out Addison’s Disease. If the cortisol is normal or high in a sick animal, it isn’t Addison’s.
However, to definitively diagnose Addison’s, we run an ACTH Stimulation test. ACTH is the hormone that is normally released from the pituitary gland at times of stress. This works on the adrenal glands and stimulates the release of cortisol. During the test we give the dog a dose of ACTH and measure the cortisol level in the blood one hour later. A normal dog will have a high level of cortisol in the blood but an Addisonian dog won’t have any corticosteroids to respond with.
Is Addison’s Disease treatable?
Yes, it is, and if well managed and monitored your dog will go on to have a full and healthy life.
The mainstay of treatment is around replacing the mineralocorticoid hormones. We will send your dog home with a product called Florinef (fludrocortisone) which is a tablet that you give twice a day for the rest of their life. We calculate the dose rate depending on the levels of sodium and potassium in the blood. We need to monitor these quite often initially, but then when your dog is stable, we only need to do the blood tests every 6 months. Luckily fludrocortisone has some glucocorticoid activity as well, so in some cases we don’t need to give additional glucocorticoids. Florinef needs to be kept in the fridge.
We do usually send your dog home with Prednisone tablets. Instructions are usually around monitoring your dog and perhaps giving them a dose when you anticipate a stressful situation for them. This could be a vet visit, a groom or even the grandchildren visiting if that is something that your dog doesn’t usually cope with very well.
You may read about a product called DOCP. This is an injection that is given by a vet every 25 days or so. A blood test is done before each injection initially but if stable this can be decreased to 2-3 times a year. This could possibly give better control than Florinef in some dogs so is an option for these patients. However, DOCP does not give any glucocorticoid action so the dogs will need to be supplemented with this daily.
What is Atypical Addison’s Disease?
This is very rare. These dogs only lose the ability to produce the glucocorticoids, and still have normal levels of mineralocorticoids. Symptoms are similar to those with typical Addison’s. These dogs are managed just with prednisone. They can progress to the typical form, so we would still need to monitor their electrolytes regularly (every 1-2 months initially).