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Atypical Addison's disease is Addison's disease in which a dog doesn't make enough cortisol but still has normal sodium and potassium on bloodwork. Without the electrolyte changes that usually give Addison's away, the signs are vague: vomiting, poor appetite, diarrhea, weight loss and low energy that come and go and often flare after stress.1,2 If your dog keeps having bouts of illness and testing hasn't found a cause, I would suggest checking for atypical Addison's. It's confirmed with an ACTH stimulation test and treated with daily prednisone, and most dogs do very well.1
Key Takeaways
Bring your dog in now if they collapse, are suddenly very weak, keep vomiting, or can't keep their prednisone down. Those can be signs of an Addisonian crisis. Call us at (519) 896-0532, or use our emergency page after hours.
Addison's disease, or hypoadrenocorticism, means the adrenal glands aren't making enough of their hormones, mainly cortisol and aldosterone. Cortisol helps the body cope with stress and keeps appetite, the gut and blood sugar on track. Aldosterone keeps sodium in the body and flushes potassium out.1
In classic Addison's, both hormones fall. Sodium drops and potassium climbs, and those changes on a blood test usually point to the diagnosis. In the atypical form, cortisol is low but sodium and potassium are still normal.1 Specialists now call it eunatremic, eukalemic hypoadrenocorticism, or EEH, which means Addison's with normal sodium and potassium.2
Vets long assumed the atypical form affected cortisol alone. Then a study of 70 dogs with Addison's found aldosterone low or undetectable in 67 of them, including the dogs whose sodium and potassium were normal.3 How those dogs keep normal electrolytes without aldosterone isn't known.3
The cause isn't proven, but we believe the immune system destroys the adrenal cortex, the hormone-making outer layer of the gland.1
In some dogs the adrenal glands are fine and the problem is the pituitary gland, which stops sending ACTH, the signal that tells the adrenals to make cortisol. This secondary form looks the same in the exam room. A blood test for ACTH tells the two apart.1
Any dog can. Females are affected more often than males, and mixed breeds are diagnosed most often overall.1 Breeds at higher risk of Addison's include the Nova Scotia Duck Tolling Retriever, Great Dane, Standard Poodle, West Highland White Terrier, Bearded Collie and Portuguese Water Dog.1 Cocker Spaniels were the most common breed in a study of 92 dogs with Addison's.6
Dogs with the atypical form tend to be older when it's found. The same study put their median age at diagnosis at 6, compared with 4 for classic Addison's.6 A North Carolina study found a similar gap: 8.3 years against 5.1.7
The signs are vague. They come and go, and stress usually makes them worse.1,2 Most dogs show some mix of:
Some dogs bleed into the gut, which shows up as black, tarry stool or fresh blood. When 151 dogs with long-term gut signs were tested, six had Addison's. Four of the six had one or the other, and none had abnormal electrolytes.4 Addison's is one of the causes to rule out in a dog with stomach ulcers or sudden bloody diarrhea.
Less often, blood sugar drops low enough to cause weakness or seizures.1 Addison's can also cause megaesophagus, where the esophagus loses its tone and food comes back up.2 In one reported Standard Poodle with the atypical form, the megaesophagus resolved once cortisol was replaced.8
Not every dog shows every sign, and many look perfectly well between episodes. That's a big part of why this form gets missed.
Dogs with the atypical form are much less likely to arrive in crisis. Classic Addison's often shows up as an emergency, with collapse, shock, weak pulses, a low body temperature and extreme weakness.1 The atypical form tends to creep in instead, with repeated bouts of vomiting, poor appetite or diarrhea before anyone makes the diagnosis.
A study of 92 dogs compared the two forms at the time of diagnosis:6
| Atypical (20 dogs) | Classic (72 dogs) | |
|---|---|---|
| Median age | 6 years | 4 years |
| Lethargy | 65% | 72% |
| Poor appetite | 40% | 61% |
| Vomiting | 30% | 73% |
| Drinking and urinating more | 20% | 11% |
| Raised urea, a kidney value | 25% | 72% |
The dehydration of classic Addison's pushes kidney values up, which can look like kidney disease on a blood test. Dogs with the atypical form are far less likely to show it.1,6
In both forms, dogs cope poorly with stress. The body relies on cortisol to handle it, so vomiting, diarrhea, poor appetite or lethargy often follow a stressful event.1,2
An ACTH stimulation test confirms it, and it's the test we recommend. Your vet takes a blood sample, injects synthetic ACTH, the hormone that tells the adrenal glands to release cortisol, and takes a second sample an hour later.1 A healthy dog's cortisol climbs. In a dog with Addison's it barely moves, and the second result stays under 2 µg/dL (55 nmol/L).1
A resting cortisol is a simple first step. If a single sample comes back above 2 µg/dL (55 nmol/L), Addison's is effectively ruled out.1,2 Below that, the stimulation test comes next, because plenty of sick dogs without Addison's have a low resting cortisol.1,4 Among 151 dogs tested for long-term gut signs, 42 had a resting cortisol under 2 µg/dL, and only 6 turned out to have Addison's.4
Routine bloodwork can drop hints. A sick dog's lymphocyte count normally falls with stress, and in a dog with Addison's it often doesn't. Mild anemia, low albumin, low cholesterol and low blood sugar are other clues.1 None is reliable on its own. In the 92-dog study, each appeared in only 10% to 35% of dogs with the atypical form.6
Because the signs overlap with so many stomach and bowel problems, including pancreatitis and inflammatory bowel disease, I would recommend adrenal testing early for any dog whose vomiting or diarrhea keeps coming back.4
Yes. Prednisone and similar steroids suppress a dog's own cortisol production, so a dog that has had them recently can test like a dog with Addison's.5 Researchers testing 112 dogs with long-term gut signs found that 11 had been given steroids beforehand, and 2 of those 11 falsely tested positive.5
One had been on prednisolone for seven months with six days off before the test. The other had a four-day course. Both tested normal once they'd been off steroids for longer.5 A board-certified internist writing in Today's Veterinary Practice recommends tapering steroids off and waiting at least three weeks before an ACTH stimulation test.2 Measuring the dog's own ACTH can help sort out a borderline result.5
Tell your vet about every steroid your dog has had recently, including short courses. For the same reason, adrenal testing should come before a steroid trial for suspected bowel disease, not after.
Daily prednisone, a corticosteroid given by mouth, replaces the cortisol your dog can't make.1 Dogs usually start on a higher dose that's tapered over the first few days to the lowest dose that controls the signs. The long-term dose is small, typically 0.05 to 0.2 mg per kg a day.1,2
Too much prednisone causes side effects of its own, and most owners in the North Carolina study reported some.7 If you notice them, tell your vet rather than changing the dose yourself.
Your dog's sodium and potassium also need rechecking from time to time, because aldosterone production can fail later.1 Some dogs need aldosterone replaced from the start. Three of the 20 dogs with the atypical form in the 92-dog study had low aldosterone at diagnosis and were started on DOCP (desoxycorticosterone pivalate), the injectable treatment used for classic Addison's.6,7
Prednisone doesn't cure atypical Addison's disease, and treatment is lifelong.1,2 It does let dogs lead normal, happy lives.
Yes. Some dogs with the atypical form later lose aldosterone too. Sodium falls, potassium rises, and the disease becomes classic Addison's.1,2
A study that followed dogs with the atypical form for a median of three and a half years found that 4 of 9 lost aldosterone function or developed electrolyte changes.6 One dog had an Addisonian crisis with high potassium two months after diagnosis. Two developed electrolyte changes at 1.4 and 5 years. The fourth lost aldosterone at 5.9 years while its electrolytes stayed normal. None of the other five was reported to have progressed by the end of follow-up.6
Nine dogs is too small a group to give a reliable rate, but progression is common enough to watch for in every dog. Signs that return or get worse despite prednisone are a reason to recheck electrolytes. Dogs that progress need a mineralocorticoid such as DOCP or fludrocortisone added to their prednisone.1
Life with a treated dog is mostly normal. In the North Carolina study, dogs with the atypical form lived a median of 5.6 years after diagnosis, compared with 5.7 years for dogs with classic Addison's.7 Only nine dogs with the atypical form were in that analysis, but the result fits what the Merck Veterinary Manual calls an excellent long-term outlook.1
Stress takes the most managing, and in dogs it isn't always obvious. It can be a move, boarding, travel, the loss of a family member, surgery or an illness.
During stressful events, we often recommend temporarily increasing the prednisone dose. Doubling it for the stressful period is a common approach.2 Ask your vet ahead of time what to give, based on your dog's current dose and weight, so the plan is ready before you need it.
If your dog keeps having unexplained bouts of vomiting, poor appetite or low energy, call us at (519) 896-0532. A resting cortisol is a simple place to start.
Yes. That's atypical Addison's disease, now often called eunatremic, eukalemic hypoadrenocorticism. The dog doesn't make enough cortisol, but sodium and potassium are still normal when it's diagnosed. Aldosterone is often low anyway, and some dogs develop electrolyte changes later, so normal electrolytes don't rule Addison's out. A resting cortisol above 2 µg/dL (55 nmol/L) does, and an ACTH stimulation test confirms the diagnosis.
Most dogs live a normal life with daily treatment. In a North Carolina study, dogs with the atypical form lived a median of 5.6 years after diagnosis, almost the same as the 5.7 years for dogs with classic Addison's. Only nine dogs with the atypical form were in that analysis, but it fits what the Merck Veterinary Manual calls an excellent long-term outlook for dogs on treatment.
Yes. Both cause vomiting, diarrhea, poor appetite and weight loss that come and go. In a study of 151 dogs with gut signs lasting more than three weeks, 6 had Addison's, and none of the six had abnormal electrolytes. A second study found it in 1 of 112 similar dogs. Adrenal testing should come before a steroid trial, because steroids given first can make a dog without Addison's test positive.
Yes. The adrenal glands don't recover, so the missing cortisol has to be replaced every day for the rest of your dog's life. Skipping doses or stopping suddenly can bring the signs back or trigger a crisis. The long-term dose is small, and it's raised for a short time during stressful events.
Usually not when it's first found. Dogs with the atypical form tend to have milder, slower signs than dogs with classic Addison's. It can become one, though. A dog that collapses, is suddenly very weak, keeps vomiting or can't keep its prednisone down needs to be seen right away. In one study, a dog with the atypical form had an Addisonian crisis two months after diagnosis.
No. Stress doesn't damage the adrenal glands, but it does expose the problem. The body relies on cortisol to cope with stress, so a dog that can't make enough often gets sick during or after a stressful event such as boarding, travel or surgery. That's why dogs with Addison's get extra prednisone during stressful periods.
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