Current Vet

In this episode, Dr. Lottie walks through how Addison’s disease develops, why it is known as the ‘great pretender’ and the best tests for diagnosis

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Timeline:
00:00 Intro
00:52 Case
02:20 Aetiology & Pathogenesis
05:48 Clinical Signs
07:38 Diagnosis
11:19 Treatment
15:13 Key Points
16:42 Outro

Recommended Reading

References

Current Vet is an educational podcast intended for veterinary students, veterinary professionals, and individuals with an interest in veterinary medicine.

All content provided in this podcast and its associated materials is for educational and informational purposes only. It is not intended as, and must not be considered a substitute for, professional veterinary advice, diagnosis, or treatment.

Any clinical cases discussed in this podcast are fictional, and are designed to reflect typical or likely clinical scenarios for educational purposes. They do not represent specific real-life cases, clients, or animals.

While every effort is made to ensure accuracy and alignment with current evidence at the time of publication, veterinary medicine is a rapidly evolving field, and recommendations may change over time.

Creators and Guests

Host
Dr. Lottie Wilkinson
Creator and host of the Current Vet podcast

What is Current Vet?

The podcast that makes veterinary medicine simple.

In each episode, Dr. Lottie breaks down clinical conditions, cases, and concepts across species, focusing on pathophysiology, decision-making, diagnostics, and what actually matters in practice. It’s the kind of context that makes your knowledge finally click.

Every month, we’ll also have honest conversations with guests about the incredible variety of veterinary medicine, what you can do with a vet degree and how to think bigger about your career.

Whether you’re cramming for exams or looking for a soundtrack for your dog walk, Current Vet will make veterinary medicine simple

Intro

[00:00:00] Hello, hello and welcome back to Current Vet, the podcast that makes veterinary medicine simple. I'm your host, Dr. Lottie, and today's episode is all about canine Addison's disease, or more formally known as hypoadrenocorticism. Now, if Cushing's disease is about too much cord, so Addison's is the complete opposite.

And it's a condition where the adrenals don't make enough of the hormones they are supposed to produce. It's sometimes called the great imitator or the great pretender because the signs associated with it can be quite vague and it's easy to get it confused with other conditions,

but let's understand what artisans actually is and how we can actually recognize these cases. So let's jump straight into our case.

Case

It's a Monday morning and your first consult of the day is Pebble, who is a very sweet, 4-year-old female neutered [00:01:00] Portuguese water dog. Her owner, Mr. Collins, says she's been off for a few weeks now. Nothing dramatic. She's just a little bit quiet, not quite finishing her meals and occasionally vomiting after eating.

She had some diarrhea last week, but that cleared up on its own. She now just seems to be a little bit tired all the time. On clinical exam, pebble is quiet but alert. Her temperature is normal, but her heart rate is surprisingly low For how nervous she usually is in the clinic. Only around 60 beats per minute.

Her gums are a little bit pale. Her capillary refill time is slightly raised at two and a half seconds and her pulses feel a little bit weak. You also notice her abdomen is slightly tense on palpation, although there is no obvious pain. You check her history, and she's been in a couple of times over the past year for vague GI signs, one bout of vomiting, another bout of diarrhea, but [00:02:00] nothing that seemed to be a really big red flag.

And she's always bounced back with a bland diet and supportive care. So you're looking at a youngish dog with waxing and waning GI signs, lethargy, and an unexpectedly low heart rate. now that we've met Pebble, let's talk about what Addison's disease actually is.

Aetiology & Pathogenesis

The full term is hypoadrenocorticism.

And just like with Cushings, the name tells us exactly what's going on. So hypo means below normal adrenal refers to the adrenal glands, and cortis relates to the cortex of the adrenal glands. So altogether hypo adrenal cortis means that the adrenal cortex is underactive and not producing sufficient levels of hormones.

There are three layers of the adrenal cortex, and each one produces one of the main [00:03:00] classes of steroid hormones, so mineral corticoids, mainly aldosterone, are produced from the Zona glomerulosa, which is the outer zone. The middle zone is the Z of fasa, which produces glucocorticoids, which is mainly cortisol, and then the inner cortical zone is the ZR reticularis, which produces androgens In Addison's disease, dogs either don't produce enough cortisol or they don't produce enough cortisol and aldosterone.
So classic Addisons is a deficiency in both cortisol and aldosterone, whereas atypical Addisons is only a deficiency in cortisol with normal aldosterone production. This lack of hormone production is most often caused by immune mediated destruction [00:04:00] of the adrenal cortex. Therefore, it is classified as primary hypoadrenal cortic.

If the condition was due to pituitary dysfunction to toxins, drug administration, or a neoplasia, it could be classed as a secondary hypo renal cortic system. So let's break down the functions of these two key hormones because understanding what they should do normally helps explain what goes wrong when they are missing.

So cold cell regulates metabolism. It mobilizes energy. Protein, suppresses inflammation, maintains blood pressure, regulates blood sugar levels, and helps to support the stress response. It even alters your mood and cognitive function. Without it, dogs become lethargic, nauseous, hypoglycemic, and poorly able to cope with any kind of stress.

Aldosterone helps the [00:05:00] kidneys retain sodium and excrete potassium and hydrogen ions,
which in turn maintains blood volume, blood pressure, and electrolyte balances. Without it, sodium is lost in the urine. Potassium builds up in the blood, and hypovolemia develops, and this is what leads to the classic hyponatremia, hyperkalemia, and hypovolemia seen in Addison's patients.

Addison's is often described as the great pretender because cortisol and aldosterone have roles in almost all of the body systems. So when they're deficient, the signs are varied and vague, and they can mimic anything from GI disease to renal failure or even behavioral changes.

Clinical Signs

Now let's talk about all the different clinical signs that we may see in an Addison's dog. So the hallmark of Addison's disease is basically that [00:06:00] the signs are vague, they're intermittent, and they're non-specific, which is really not helpful, and it makes it easy to miss unless you're actually thinking about it.
So a couple of these signs that atypical of Addisons are gonna be recurrent episodes of vomiting and diarrhea, inept absence and lethargy, and because more water is being lost in the urine, that we are then gonna see hypotension, poor perfusion.

And then we're gonna see bradycardia, which can be explained by the lack of cortisol and therefore increased vagal tone. And because of hyperkalemia affecting cardiac conduction. We can also see dehydration caused by the increased loss of fluid from urine and vomiting and diarrhea. We can see collapse, poor peripheral pulses, and sometimes PUPD because of the impeded ability of the kidneys to function.

In atypical Addisons where only glucocorticoids are deficient, the [00:07:00] electrolyte abnormalities are not gonna be present because obviously our aldosterone production is normal. These cases often present just like kind of chronic GI disease, so you're vomiting, diarrhea, weight loss, lethargy, but electrolyte levels are typically normal.

Finally you should be aware of which breeds can be predisposed to Addisons. So standard poodles, Portuguese water dogs like our Pebble Nova Scotia Duck tolling Retrievers, bearded Collies, and West Highland White Terriers. And there's also a higher likelihood that it occurs in females over males.

Diagnosis

Okay, so based on Pebble's history of vague geoscience, lethargy, low heart rate, and her being a Portuguese water dog, you definitely wanna make sure that this isn't Addison's, but we kind of know it is obviously, 'cause it's an episode on Addison's. So step one is gonna be [00:08:00] hematology and biochemistry. With Addisons, we're likely to see a mild non regenerative anemia, an absence of a stress leuko, an absence, and that is a red flag. Most sick dogs have Neutrophilia, lymphopenia and But Estonian dogs have a normal or even high lymphocytes and eosinophils, which is unusual. Hyponatremia and hyperkalemia are quite classic. Azotemia due to the hypovolemia and poor renal perfusion hypoglycemia, hyperkalemia can be seen due to reduced glomerular filtration and metabolic acidosis may also be present.
Next, we can do a urinalysis and we are probably gonna see a low urine specific gravity. But this is not gonna be specific, We can then do a basal cord, so, or [00:09:00] cord. So SNAP test, and this is a really great screening test as it shows us if cord, so levels are generally low. So in a high stress environment like Lyco, vet clinic cord.

So levels really shouldn't be low in healthy patients. So if the basal cortisol level is more than two micrograms per deciliter, Addison's, it's gonna be extremely unlikely. If it's less than two micrograms per deciliter, Addison's is possible, but you need to confirm it with a definitive test. So this is really useful when Addison's is on your differential list and you want to rule it in or out.

If it's a low level, obviously, and we think Addison's is still a possibility, we then need to do further testing. So we can then do our A CTH stimulation test, which is the definitive test for Addison's. First, you're gonna measure the baseline cord cell levels. You're then [00:10:00] gonna give synthetic A CTH, and then measure cortisol levels one hour later.

In a normal dog cord, soul should increase significantly. But in a dog with Addison's, both the baseline and post a CTH cord, soul levels are gonna be low.

You run an A CTH stem on Pebble, and she has a baseline of 1.1 micrograms per deciliter and a post a CTH of 1.3 micrograms per deciliter, which confirms Addison's. If you wanna differentiate between primary and secondary Addisons, you can measure endogenous A CTH. So in primary Addisons, which is a primary adrenal problem, A CTH will be high because the pituitary gland is still trying to stimulate the adrenals to produce more hormones in Addison's caused by a pituitary problem. A CTH will be low or [00:11:00] undetectable because the pituitary gland will not be producing a CTH as normal. But in practice, primary Addison's is by far the most common, and treatment is essentially the same. So this test is not really done kind of reserved for academic interest or unusual cases.

Treatment

So our treatment approach for Addison's depends on the severity of the patient's condition.
Dogs can present in an acute emergency known as an Addisonian crisis. So if Pebble had come in, collapsed, bradycardic, and in shock, you would definitely need to act fast. So this treatment is gonna include aggressive IV therapy. So Crystal should be used to correct the hypovolemia and to dilute high potassium levels.

Calcium gluconate can be given in. If hyperkalemia is severe and there are big changes on ECG, [00:12:00] dextrose and insulin can be given to drive potassium into the cells. Although be careful with this, if there is also severe hypoglycemia, dexamethasone is given to replace the cortisol deficiency.

Do not give prednisone or prednisolone or hydrocortisone if you need to run an A CTH STEM test. As all of these options will interfere with cord cell measurements on the test, dexamethasone won't so give Dexamethasone, antiemetics and GI support can also be given. We should also be regularly reassessing these patients to make sure that they are responding to treatments and clinically improving.

Once the patient is stable, you can then transition to long-term therapies. So for Pebble who is stable but confirmed Addisonian, we now need to replace the missing hormones. So for glucocorticoid replacement, prednisolone is the [00:13:00] most common choice to. You start with a physiologic dose, which is around 0.1, 0.2 mg per kg per day, and adjust that dose based on the clinical signs.

If the owner anticipates times of stress, travel of illness, dogs need a two to 10 times higher dose. So we should be comfortable educating clients on this so they can up their pets doses confidently when they are needed. Then for Milano corticoid replacements, there are two main options.

We have Doxy, corticosterone Pate. Which is given every 25 to 30 days by a subcut injection, and this requires electrolyte monitoring at days 10 and 25 initially, just to make sure that the dose is correct, and then once the dose is stable every three to six months. A second option is flu called [00:14:00] stone, which is a synthetic steroid that has both mineralocorticoid and some glucocorticoid activity.

It's an oral medication that is given typically twice a day.

In practice, many clinicians prefer deoxy, corticosterone, pate, and prednisolone because it allows more precise control of each hormone group. It is also better tolerated long term in most dogs and means that owners aren't having to give oral flu record stone twice a day. You do need to monitor electrolytes, especially in the first few months, as with starting treatment. So signs of undertreatment and underdosing are gonna include ongoing lethargy, vomiting, diarrhea, or bradycardia. And overtreatment is gonna cause signs of Cushings, so pPD panting, muscle wasting and fat gain. We have to make sure the owners know that [00:15:00] while patients are likely to make a full recovery and have a great quality of life, Addison's is a lifelong condition and the dog will need to continue to be medicated as well as have regular rechecks with the vet.

Key Points

So what are the key takeaways that you need to know about Addison's? Addison's is Hypoadrenal Cortis, a deficiency of cortisol andone most often due to immune mediated destruction of the adrenal cortex. It's known as the great pretender because signs are vague and nonspecific. So think things like lethargy, vomiting, diarrhea, weight loss.

Classic Addisons is when there's a deficiency in both cortisol and aldosterone. And atypical Addisons is when there's a deficiency in cortisol only electrolyte abnormalities like hyponatremia. [00:16:00] Hyperkalemia should raise your suspicion. The A CTH stimulation test is the definitive diagnostic test and a flat cord cell response before and after A CTH confirms.

Addison's treatment requires replacement of these hormone deficiencies. So glucocorticoid replacement is typically with Prednisolone and mineralocorticoid replacement is typically with DOCP injections. Close monitoring is needed to make sure that the dosages are correct.

Remember, this is a lifelong condition, but once diagnosed and managed properly, dogs with Addison's can have a great quality of life.

Outro

And that is canine Addison's disease. It's subtle, it's sneaky, and it can present in many different ways, but once you understand what's happening, it makes slightly more sense.

Thank you so much for listening to Current Fat. [00:17:00] If you found this episode helpful, follow or subscribe wherever you get your podcasts. Share it with a friend or colleague and if there's a topic you'd like us to cover next, let us know in the comments or come and say hi on TikTok and Instagram at Veterinary Vista.

We'll see you next time.