Let's get to case number four. We're getting there. We have two more cases. All right. So case number four is Greta. Greta is a ten year old female spayed miniature dachshund. She is, of course, up to date on her vaccines and she has a two month history of polyuria polydipsia. She also has a history of pica, which essentially means eating things that she shouldn't. And she's recently been getting into the trash, which is a pretty unusual thing for her to do. The owners also note that she's been panting excessively at night. So here is her physical exam findings, or here are her physical exam findings, I should say. Okay. 

And here are her serum chemistry results. Give you a second to look over those. And then, of course, we have our urinalysis as well. Okay. And so in summary, over here on the right, we have the pertinent findings on our serum chemistries and urinalysis. And we also have our T4, because this was a senior panel. So we have a mild hyperglycemia with a negative urine glucose. So specifically in this case, I would be worried about a stress response. And remember, in dogs, that's typically more commonly due to an increase in cortisol. We have hypercholesterolemia, which suggests that we have an alteration in our lipid metabolism, and we have a mild to moderate increase in the liver enzymes, specifically with a moderate to severe increase in our alkaline phosphatase. And remember the alkaline phosphatase, if we go back to lecture two, is typically increased due to cholestasis or there is a specific steroid induced isoform that is only in dogs. We also have a decrease in our total T4 and as we already talked about, this may indicate hypothyroidism or a sick euthyroid syndrome. We have have isosthenuria, but because our BUN and creatinine are normal and I know they're not on here but going back a few slides, our BUN and creatinine were normal, this makes you renal disease pretty unlikely. We also have proteinuria. 

All right, so what do we think here? We have a low total T4. So, do we think that Greta is hypothyroid? So let's go back to her clinical history. And if we look at her clinical history, we'll find that she has several clinical signs that really aren't consistent with hypothyroidism. So what signs are inconsistent with hypothyroidism? Well, PUPD, we don't typically see in dogs with hypothyroidism. Panting is something else we typically don't see. And that change in her appetite that pica is also not expected with hypothyroidism. If we look at our clin path findings, there are some things that are consistent with hypothyroidism. So she is hypercholesterolemic and her total T4 is decreased. But we don't have her CBC, but I can tell you that she doesn't have a non regenerative anemia. She has isosthenuria and proteinuria, which is inconsistent with hypothyroidism. And she has a moderate to severe increase in her ALP, which is also inconsistent with hypothyroidism. So my biggest concern in her case would be that she is sick euthyroid. We could consider running a free T4 in her case. But remember that if she has other disease going on, this could still be difficult to interpret. And so in her case, what I'm going to do, I'm going to decide to not look at her thyroid anymore because I don't think the thyroid is the cause of her clinical signs. And I might consider re addressing it once we've got her other disease under control. 

All right. So our clinical signs and our clinical pathology findings are most suggestive of hyperadrenocorticism. Okay? So most commonly, on a clinical pathology, we'll see an increase in our alkaline phosphatase in about 90% of dogs who are Cushingoid or have hyperadrenocorticism. And it can be often even ten times the upper end of the reference range. So it can be significantly increased. If you remember, back to our pathophysiology, this is due to steroid induced vacuolar hepatopathy, so our hepatocytes swell and get really full of lipid and that can result in compression of our bile canaliculi, which will cause our ALP to increase. But then there's also this steroid induced isoform of ALP that we see in dogs with Cushing's or dogs who are on exogenous steroids. There's also we also might expect to see a mild increase in our ALT. Hypercholesterolemia and hypertriglyceridemia we can see in more than 50% of cases. So this is pretty common. And we may also see a mild fasting hyperglycemia. So we're not talking about a glucose in the three or four hundreds, although you can have diabetes and Cushing's together. But Cushing's in and of itself only causes a mild increase in your blood glucose. 

The other things that we see fairly commonly are a stress leukogram and thrombocytosis, so an increase in our platelet count on our CBC. Our urine specific gravity is less than 1020 typically. So we typically got a decreased or an isosthenuric urine specific gravity. Proteinuria is very common and if we perform a urine protein creatinine ratio and you can go back to lecture three to look more at that, we would expect to see it mildly increased. It's very common actually in Cushing's to see a decrease in our total T4 because steroids affect our thyroid metabolism. 30 to 50% of cases actually have a decrease in their BUN. And that's due to the diuresis that we see associated with hyperadrenocorticism. 40 to 50% of dogs with Cushing's will have a UTI at the time of diagnosis. And so remember, just like in diabetes, they often have isosthenuria with an inactive sediment due to immunosuppression. And so it's really important that we culture the urine, even if the sediment is inactive. 

All right. So this is the this is the tricky part. Okay? So how are we going to diagnose hyperadrenocorticism in our patients? And what's really important to remember is the test that you do really matters. Okay? So you have to select the right test. No single test is 100% diagnostic. Okay? So very importantly stress and concurrent disease will affect our hypothalamic pituitary adrenal axis, which is right here. Okay. And so they can give you a false positive result. All right. So if you have a sick dog and you're screening them for Cushing's, don't, because you're not going to be able to interpret that result. So one of the most important things to remember when you are screening a dog for Cushing's is whether or not you think it's Cushingoid. So if you run testing in a dog that you have a low clinical suspicion of Cushing's and you get a positive result, you really have to consider whether you think that that positive result is due to primary adrenal disease or due to other disease affecting the adrenal axis. So it's very, very important to appropriately select the case before you decide whether you're going to run further testing. Now there are three tests that are commonly available to screen for hyperadrenocorticsm. There is the urine cortisol creatinine ratio, the ACTH stimulation test, and that should say creatinine, I'm sorry, not creatine. And the low dose dexamethasone suppression test. 

So let's look at the use of the UCCR, the urine cortisol to creatinine ratio. The way that we run this test is that the owner is going to collect a free catch urine sample at home. Really, really important that the sample is collected when the patient is not stressed. So what you don't want the owner to do is to go home and collect that urine sample as soon as the dog gets home, because stress of being in the veterinary hospital is going to increase your cortisol, increase the cortisol in your urine and give you a false positive result. So if you're going to run this test, you want to separate it by several days from that veterinary visit. We submit the urine cortisol creatinine ratio to a reference lab. The urine cortisol creatinine ratio here has a really, really limited applicability, in my opinion. I never use it as a test to diagnose Cushing's. I use it as a test to rule Cushing's out. So what do I mean by that? The false positive rate with this test is very, very high. And so what that means is that an increased UCCR can be due to any number of factors and only about 25 to 30% of dogs with an increase in the UCCR truly have Cushing's. On the other hand, the false negative rate is very low. So if I have a negative result, I can fairly feel fairly confident that I'm ruling out hyperadrenocorticism. Okay? So if I have a low index of clinical suspicion, so if I don't really think a dog is cushingoid, but I sort of want to get a little bit more information, this might be an appropriate test to run. If I have a dog who I think is cushingoid, I'm not going to run this test because it's not a test that is going to definitively diagnose an overactive adrenal gland for me. So what else can I do? 

We could consider running an ACTH stimulation test. So the ACTH stimulation test is testing our adrenal cortex response to ACTH. The way that we do it is we draw a baseline serum sample. We administer five micrograms per kg of cosyntropin IV, and this is essentially synthetic ACTH. Then we're going to draw a post simulation serum sample one hour after administration of ACTH. During the test, we're going to keep the dog quiet and relaxed as much as possible. Sometimes I'll even have dogs sit in the car with the owner for that one hour or sit in the waiting room with the owner for an hour, depending on where they are less stressed to try to minimize the effects of stress on the test results. Now the specific normal ranges for your cortisol vary by lab, but generally speaking, the baseline is considered to be between one and six. And I honestly don't really look at my baseline very much. What I'm looking at is my post stimulation results. And so generally speaking, in dogs with hyperadrenocorticism, we see a post stimulation result, in this example, these are just numbers from one particular lab, significantly higher than 22 micrograms per deciliter. 

So if we go back to pathophysiology, dogs with hyperadrenocorticsm have an increase in their functional adrenal tissues. So that most commonly is due to adrenal hyperplasia due to an increase in circulating ACTH, due to a pituitary adenoma. I'm sorry. Go back. Where did I go? Oh, where did it go? Sorry. Hang on. Where did my little slide go? There it is. Hey. All right, so we have a pituitary adenoma again that's secreting increased amounts of ACTH, and so our adrenal glands are going to increase their production of cortisol in response to that. When we give ACTH, so cosintropin is our synthetic ACTH, we're maximally stimulating our adrenal glands that are already hyperplastic. And that means that when we maximally stimulate them, they have more ability to produce cortisol. And so when we measure our cortisol in blood, it's significantly increased. Similarly, if we have an adrenal tumor, so we have one large adrenal gland that's producing cortisol that may also respond to extra physiologic doses of cosintropin that will similarly increased the cortisol. So we are never going to interpret a baseline cortisol because it's going to be influenced by many different factors. We're going to look at that post stimulation cortisol to give us an idea of whether this adrenal tissue is being is is bigger than it should be, or if there's more adrenal tissue than should be there or if the adrenal function is normal. Okay, so we're giving this cosintropin to these adrenal glands that are overactive and we're looking for an increase in our cortisol when we do that. 

All right. So as we already talked about, stress or chronic disease can give us a false positive result. And so that's, you know, something we always have to bear in mind. And so that, again, comes back to our case selection. If we're not selecting our cases appropriately, we are potentially going to get a false positive result that's going to be very hard to interpret. Sometimes dogs with adrenal tumors do not have a an increase in cortisol production due to us giving ACTH because their adrenal tumor is completely independent of ACTH. So we can see a false negative in those cases. And so the sensitivity for detecting an adrenal tumor in dogs with an ACTH stimulation test is only 60%. So we're missing a fair number of cases there. It's better with pituitary dependent disease. So in dogs with pituitary dependent disease, it's about 85% sensitive in those cases. What an ACTH stimulation test can't do is tell us whether this is pituitary or adrenal dependent disease. Even so, even with those limitations, there are some things that make the ACTH stimulation test good. First of all, it's really easy to perform. It's a one hour test and so it's much easier to perform than the next test that we're going to talk about in a second. It's more sensitive and specific than a urine cortisol creatinine ratio. And that's the only test that can diagnose iatrogenic hyperadrenocorticism. So iatrogenic hyperadrenocorticism occurs when we're giving a dog steroids. So sometimes you know you look at a dog that's been on chronic steroids and you're not sure is this a clinical picture due to me giving the dog steroids or is now the dog cushingoid as well? And the ACTH stimulation test is the appropriate test to use to figure that out. What we would expect to see in that case, if it was just iatrogenic hyperadrenocorticsim, is that we wouldn't see a response because of the negative feedback from the exogenous steroid on our pituitary adrenal axis. So we would expect to see a minimal response even in a dog that looks Cushingoid. That would be tell me that it was because of the steroids that I was giving rather than primary adrenal disease giving me that clinical appearance. 

All right. And then the final test, which I think is a test that everybody gets a little bit scared about, is the low dose dexamethasone suppression test. Hopefully, I'm going to make this less complicated for you today. The way that we run our low dose dexamethasone suppression test is that we draw a baseline serum sample. We administer .01 mgs per kg of dexamethasone intravenously. And then we draw a serum sample at 4 hours and 8 hours. So if we look at our axis again, when we administer dexamethasone, which is an exogenous steroid, we would in a normal dog expect that we would suppress our adrenal axis. So negative feedback means that we would decrease our production of CRH from the hypothalamus, decrease ACTH from the pituitary, and we would measure a decrease in our glucocorticoids. So again, these normal ranges vary by lab, but our baseline cortisol is always going to be the same. It's going to be between 1 to 6 being considered normal. Our 4 hours post sample, generally speaking, we consider less than 1.4 micrograms per deciliter or less than 50% of the baseline as being normal. And our eight hour post being less than 1.4 micrograms per deciliter or less than 50% of the baseline as well. So the four hour and the eight hour post have similar normal reference ranges of the same normal reference ranges. 

So as we already talked about with that negative feedback loop, if you have hyperadrenocorticism, the suppression of your adrenal axis is not going to happen when you give exogenous steroids. So that dexamethasone that you give is not going to suppress your axis. And so we're going to see a lack of suppression. All right. So the way that we're going to interpret a low dose dexamethasone suppression test and you're going to do this every time and if you do it this way, you're not going to get yourself into trouble. The first thing you're going to do when you do a low dose dexamethasone suppression test, when you get the results in front of you is look, look at your eight hour cortisol. So if our eight hour cortisol is less than 1.4 micrograms per deciliter or it's less than 50% of the baseline, hyperadrenocorticism is very unlikely. Okay. So we're just looking at our eight hour right now and not talking about our four hour, we're just looking at that eight hour. So if this is less than 1.4 or less than 50% of the baseline, we're going to think about whether or not we are going to rule out hyperadrenocorticsm. But potentially this would rule out that disease for us. If, on the other hand, if our eight hour cortisol is greater than 1.4 or is greater than 50% of the baseline, that would be a result that we would consider to be consistent with hyperadrenocorticism. Okay. And then we're just talking about 8 hours. So if our eight hour is greater than 1.4 we're then going to look back at our four hour. So you're only going to look at your four hour after you've looked at your eight hour. Okay. So were firs going to look at our eight hour and say, do we think hyperadrenocorticsm is likely or unlikely? And then we're going to look at the four hour for additional information. What the four hour tells us is whether or not we can differentiate pituitary dependent from adrenal dependent disease. We're only going to interpret our four hour cortisol if our 8 hour suggests hyperadrenocorticsm. If we suppress at 4 hours, so that means if our four hour cortisol is less than 1.4, or less than 50% of the baseline, that indicates that we have pituitary dependent disease. Okay. So suppression at 4 hours is suggestive of pituitary dependent disease, whereas a failure to suppress at four hours may be due to pituitary dependent or adrenal tumor. So the only time we can really use this as a differentiating test is if we have suppression at 4 hours. And if that's the case, then we can say that we have pituitary dependent disease. 

So what's the problems with our low dose dexamethasone suppression test? It's a time consuming test, so the patient has to be in the hospital all day long. We have to be able to remember to draw those blood samples at four and 8 hours. Because the animal is going to be in the hospital all day, the risk of a false positive is maybe a little higher because stress can have more of an effect on the test because potentially your patient is sitting in their cage panting all day. You also may see a positive result with non adrenal disease. And the problem is, is that the specificity, if you have non adrenal disease, is pretty low, which means that there's a fairly high false positive rate, if you have non adrenal disease present. And this again comes back to appropriate screening of your patients and running this test in the right population. Even so, if you look at your, you know, textbooks and you look at what's written about hyperadrenocorticsm, generally speaking, the low dose dexamethasone suppression test is the treatment is the test of choice. It's the most sensitive test. So it has a 90 to 95% sensitivity for pituitary dependent disease and almost 100% for adrenal dependent disease. If you're lucky, it may help you differentiate between pituitary dependent and adrenal dependent disease. 

So after we run a low dose dexamethasone suppression test, we want to differentiate if the disease is pituitary dependent or is adrenal dependent. And that's important because of prognosis and because of treatment. Now, we're not going to get into that today. That's more talking about the disease itself. We're focusing on the clin path today, but that's something that if you're not familiar with it, I would encourage you to read more about that. Now, it's important to remember is that most cases, 80 to 85% of dogs with Cushing's do have pituitary dependent disease. Okay? There are three tests that we can use to look at our pituitary versus adrenal dependent disease. Now, what's important to remember here is that realistically, I would say that these days, 99% of the time I'm using an abdominal ultrasound to help me differentiate because it's going to give me a lot of other information as well. However, if we wanted to look at running lab tests, the two lab tests we could use would be the high dose dexamethasone suppression test or an endogenous ACTH level. 

A high dose dexamethasone suppression test is essentially the same as the low dose, but we're giving a ten times dose of dexamethasone. So instead of giving .01 mgs per kg, we're giving .1 mgs per kg. We're again going to look, and you can only use this as a differentiating test. This is not a diagnostic test because we're looking for suppression at either 8 hours or 4 hours. So in this case, we're looking at suppression at either time. Suppression at either time indicates that we have pituitary dependent disease. However, if you don't suppress, it doesn't mean that you can't have pituitary dependent disease. So if you do suppress, you can say it's pituitary dependent. If you don't, it could still be pituitary dependent or it could be adrenal. So I've got to be honest, in practice, I pretty much don't run high dose dexamethasone suppression tests. The endogenous ACTH level. If we think about our our pathway, we would expect to see two different results. So if we have a positive low dose dexamethasone suppression test and then we run an endogenous ACTH in a dog with pituitary dependent disease, we would expect a normal to an increased level of ACTH because the pituitary is making excessive amounts of ACTH. But with an adrenal tumor, the cortisol from the adrenal gland is turning our pituitary off. And so we would expect the ACTH level to be low or undetectable. So that would help us distinguish between these two. Again, this is not a diagnostic test. This is a differentiating test. The problem is that ACTH is fairly persnickety. And so if we don't handle the sample correctly in there are fairly strict sample handling guidelines, our ACTH can be falsely lowered. And so that may give us, you know, an inappropriate result. So I've got to be honest, I don't run this test very regularly either. 

The tests that I do run, though, is an abdominal ultrasound. And the reason for that is that we can get a lot more information from that. We can look at our adrenal glands and we can look for our adrenal size and appearance. So with pituitary dependent disease, we're looking for a bilateral adrenomegaly. With an adrenal tumor, we're looking for a unilateral, so one sided, adrenal enlargement with the other side having a very small gland. Now, not everybody reads the rule book, and this isn't 100% the case, but for the purposes of NAVLE® and for this lecture, this is how we're going to differentiate between the two. We can also assess other organs. This is a dog who often has increased liver enzymes, so we can look for other evidence of liver disease. We know that dogs with Cushing's can be predisposed to getting biliary mucoceles, so we can look for that. Pancreatitis is also a common concurrent disease. We can look for that. And often because these dogs have well, there's two reasons why they can get cystic calculi. They can have calciaresis, which can make them get calcium oxalate stones. Or they can have chronic UTIs and that can make them more likely to have struvite stones. So we can look for cystic calculi as well with our ultrasound. 

So in Greta's case, we have these results. We have a pre-cortisol of 3.4, a four hour post of 1, and an eight hour post of 3.2. So the first thing we're going to do is look at our 8 hour post. Our eight hour post is 3.2. So there's been a failure to suppress. We would expect this to be less than 1.4 or less than 50% of baseline. It's neither of those things. And so that eight hour post, that 3.2 indicates that we have a positive result. Now we can look at our four hour to try to differentiate between pituitary dependent and adrenal dependent disease. So in Greta's case, this four hour post is 1, which is less than 50% of the baseline and is also less than 1.4. So she does suppress at the four hour. And so what that tells us, if you remember back, is that she has pituitary dependent disease. So this is a dog with hyperadrenocorticism and we can further categorize this as pituitary dependent disease. I will still perform an abdominal ultrasound because I still want to look at those adrenals and looks for concurrent disease. But if money is a severe issue, this is a dog that we could potentially start treatment with based on this diagnostic information. All right.