Hey what’s going on guys? Today we’re going to talk about Cushing Syndrome, but we’re not going to go over the entire spectrum of the Cushing Syndrome. We’re simply going to talk about how to work somebody up and then find the etiology of Cushing Syndrome. Now, very quickly, you should be aware that Cushing Syndrome is defined as any type of hypercortisolism that is not due to a pituitary adenoma. If it is due to a pituitary adenoma, then we have Cushings Disease. That is the only distinction between syndrome and disease. The clinical features are going to be the same.
Alright, so you have somebody that you suspect of having Cushing Syndrome. There’s going to be two types that you need to know of:
1. ACTH dependent, meaning that they need ACTH to have high cortisol levels. These are going to be from pituitary adenomas or from a tumor in the lungs.
2. ACTH independent Cushing Syndrome, meaning you have a syndrome that does not rely on ACTH secretion. So, it doesn’t care what ACTH is doing, it’s still going to have a high cortisol level. This can either be due to iatrogenic causes or exogenous use like prednisone or you’re going to have a tumor in the adrenal glands.
The first step is to rule out any type of iatrogenic cause. Like we stated earlier, prednisone is the most common medication, and that’s going to be very simple to differentiate in your stem. You’re going to have somebody that’s going to be with either rheumatoid arthritis or lupus, and they are on chronic daily prednisone use. This is going to be very easy to differentiate.
So once you’ve ruled that out, the next step is to order two of these three screening tests: 24 hour urine free cortisol, low dose dexamthasone test, or late night salivary test. Pick either two that you want. We need two positives in order to move on to the next step. The first one is going to be a 24 urine cortisol. You’re going to hand the patient a jug, have them collect urine for 24hours and send that to the lab. If you have any value that’s over three times the upper limit of normal, then you have a positive screening test for hypercortisolism. If it’s less than three times the upper limit of normal, then you don’t have a positive test. The next option is going to be a low dose Dexamethasone Test. You’re going to give one milligram of Dexamethasone at around 11pm the night before, have the patient come in the morning and draw cortisol levels. If the cortisol is over 1.8 we have a positive screening test and again we hypercortisolism. Now, what you’re doing with the dexamethasone – normally a healthy person should have ACTH suppressed with a low dose dexamethasone test. If you have suppressed ACTH levels, this will result in low cortisol levels as well. In a patient with Cushing Syndrome or disease, the low dose dexamthesaone will not suppress ACTH, meaning we’re going to have high cortisone levels. The next one is going to be a late night salivary; this is taking advantage of the fact that normal patients have the lowest levels of cortisol at night. So, we’re going to take a swab, swab the saliva, and send that to the lab. If we have a high cortisol level again, that is a positive screening test. You need two positive screening tests to confirm the diagnosis of hypercortisolism.
Once we have hypercortisolism, we move on to the next step: order ACTH levels. Now you can either have low ACTH levels or high ACTH levels. If you have a low level, this means this is independent of ACTH. This means it doesn’t matter what ACTH is doing, we will still have a high cortisol level. This means we have a tumor in the adrenal glands. The next step, order a CT of the adrenals.
If you have a high ACTH level, that means this is dependent, which means this needs ACTH to produce high cortisol levels. This means we have either pituitary adenoma or we have a tumor in the lungs. So if we have high ACTH, the next step is going to be high dose dexamethasone test. The low dose was 1 milligrams and the high dose is 8 milligrams. It’s done the exact same way, however, here we’re taking advantage of the fact that a pituitary adenoma will be suppressed. We give 8 milligrams, and if we have a low cortisol, that means this test suppressed cortisol levels; this means we have a pituitary adenoma, order an MRI of the pituitary gland. If you do a high dose dexamethasone test, but you have no suppression, meaning no suppression in cortisol, then you have a tumor in the lungs and you’re going to order an MRI or CT of the chest.
Alright guys, that was a quick overview of the work up, this is by far the most important part of Cushing Disease/Cushing Syndrome, this is going to be heavily tested on your exams, on the boards. They want you to know that if you see somebody with the clinical suspicion of Cushing Syndrome or disease, you know how to work these patients up. So that is the quick overview, go back and hear it again. This is very heavily tested. Alright guys, I’ll check you guys on the next video, hope this made a lot of sense and I hope this helped you guys out.