The adrenal glands sit next to the kidneys in a dog or cat's abdomen.  They are made up of a cortex, or outer layer, and medulla, or inner layer.  The cortex is responsible for secreting sex steroids (estrogen and testosterone) and cortisol (natural adrenaline), and the medulla is responsible for secreting mineralocorticoid hormones that help regulate salt and water balance in the body.  The pituitary gland in the brain is responsible for helping to regulate how much hormones the adrenal glands produce (essentially is the on/off switch).

With Addison's disease, the adrenal glands atrophy, or wither away, and do not produce enough of the hormones necessary for the body to function normally.  Since cortisol is needed to adapt to stress, these dogs tend to become sick even with the slightest stressors.  At least 90% of the adrenal cortex must be damaged before clinical signs occur.  Without mineralocorticoids, dogs lose the ability to regulate their salt (sodium) and water balance, and electrolyte problems occur.

Addison's disease is called "The Great Imitator" because the symptoms often appear very similar to many other disease processes, so diagnosing Addison's can be a challenge.  Dogs are usually younger (4-6 years of age at diagnosis) but can be as young as 6 months or older than 6 years.  Female dogs are twice as likely to get Addison's as male dogs, and Standard Poodles and Bearded Collies are predisposed.  The following are very common symptoms we see, but please realize that any chronic symptoms could be seen with Addison's disease.

• Most often is a waxing and waning illness
• Listlessness, lethargy
• Vomiting or diarrhea
• "Just doesn't act like himself" is the most common complaint we get!

Addisonian Crisis
When Addison's disease has been present for a while without treatment (which happens quite often due to the mild and vague early symptoms), pets can go into a crisis mode that includes collapse, circulatory shock, heart arrhythmias, electrolyte imbalances, and possibly death.  This is an emergency situation that needs to be treated immediately. 

The first test we will run if we suspect Addison's in your pet is routine bloodwork.  This includes a complete blood count and chemistry panel.  In addition we will recommend a urinalysis.  There are several abnormalities such as low sodium, elevated potassium, and dilute urine that are suggestive of Addison's but can also occur with other disease processes.  Pets who present in an Addisonian crisis will have bloodwork results indicative of kidney failure, so this can make diagnosis challenging.

The definitive test for Addison's is an ACTH stimulation test.  With this test, we take a baseline blood sample to test the cortisol levels (which will be low in Addisonian dogs), and then administer a synthetic ACTH hormone.  The ACTH hormone in normal dogs will stimulate the adrenal glands to increase their production of cortisol.  In dogs with Addison's disease, the adrenal glands have atrophied and no amount of ACTH will increase cortisol production, so these dogs will not have an increase in their cortisol levels following the stimulation test.

Treatment for Addison's includes replacement of both cortisol and mineralocorticoids.  Daily supplementation with a steroid is needed for the rest of the pet's life.  Mineralocorticoids can be administered via a monthly injection or by combining the steroid and mineralocorticoid into pill form.  Initially, electrolyte levels will need to be checked weekly until a stable level is reached, and then bloodwork testing is usually recommended once to twice yearly depending on how your pet is doing.  During periods of stress (thunderstorms, boarding, road trips, etc.), steroid administration may need to be increased to deal with the additional strain on the body.

Addisonian Crisis
Treating a pet who is in an Addisonian crisis can be challenging, but luckily most respond well if treatment is given early on.  Treatment includes aggressive intravenous fluids, steroid administration, and potentially insulin to lower dangerously high potassium levels.  These pets need supplemental heat and close monitoring with repeated bloodwork until they are stable. 

In a weird twist, some dogs get an unusual reaction to whipworms (intestinal parasites) that mimics an Addisionian crisis.  If your pet is not on a monthly preventative that kills whipworms, or if there are whipworm eggs found on a fecal floatation, treatment for whipworms needs to be done in addition to stabilization for the shock crisis.  If there is any doubt, treating with a dewormer cannot hurt.  Whipworms can be hard to identify because females do not constantly shed eggs so routine fecal exams can miss some whipworm infections.  Animals with whipworm infections will have normal ACTH stimulation tests.