They say things come in threes and such was the case last week. Hydi, Molly, and Dixie were all in for Cushing’s tests. Cushing’s is a disease where too much cortisol is produced by the adrenal gland. Cortisol is a natural steroid produced by the adrenal glands, but too much cortisol can cause an increase in drinking (and peeing), eating (and weight gain) and depresses the immune system. This can mean more secondary infections especially urinary tract and skin infections. Dogs (Cushing’s is rare in cats) can also cause excessive panting. A distended abdomen or pot-bellied appearance is due to loss of elastinogen fibers in the skin. Bilaterally symmetrical hair loss (without itching) may occur. Typically it is for older dogs.
The diagnosis can be difficult. Cushing’s dogs can look very normal in the exam room until they are very far along in the disease process. And the disease comes on so gradually, it is often missed at home, or the owners think the dog is just getting old. Good communications with your vet must happen to diagnose Cushing’s. Other common signs can include hepatomegaly, muscle weakness/atrophy, systemic hypertension, lethargy, hyperpigmentation of the skin, comedones (black growths), thin skin, poor hair regrowth, and pyoderma. When it comes combined with insulin resistant diabetes mellitus, it is extremely difficult to treat.
Less common signs include thromboembolism, ligament rupture, facial nerve palsy, pseudomyotonia, testicular atrophy/persistent anestrus, pituitary macro tumor syndrome and bruising. I remember drawing blood on a dog at my second practice. The dog jumped around a bit, but even then I was good at drawing blood. The next morning, the dog had bruising all around the venipuncture site. The dog had Cushing’s, but my boss told the Mrs owner the bruising was my fault because I had drawn blood.
Sometimes there are lab abnormalities on the chemistry, but sometimes the test is normal. Just because it has those lab abnormalities, does not mean that your dog has Cushing’s. In short, it can be challenging to diagnose. So, we hadn’t seen any Cushing’s dogs for a while and then there were three. Dixie and Molly had been having accidents in the house. That was very unlike either of them. They had been housebroken for years. Hydi was a new patient to us, but it seemed like her Cushing’s wasn’t quite under control.
Testing for Cushing’s is not easy. Although it is a disease of too much cortisol, measuring a resting or baseline cortisol is useless. Urine cortisol to creatinine ratio can be used to screen for Cushing’s but is not diagnostic. (IF it is positive they might have it. If it is negative, they do not have Cushing’s.) But the low-dose dexamethasone suppression (LDDS) test and the ACTH stimulation test are then used to diagnose Cushing’s. If needed a high dose dexamethasone suppression tests can add information about the patient. Sometimes the adrenal gland can be seen on ultrasound. To make it more confusing, sometimes systemic illness results in false positive results.
To test for Cushing’s we draw a baseline cortisol sample, then inject dexamethasone or cortrosyn (synthetic ACTC) and wait and draw blood and wait and collect more blood. The blood serum or plasma has to be removed from the red blood cells within 30 minutes and then it has to stay cold. The wait times are fairly rigid about when blood is needed. Of course, if we could sit around and watch the clock all day, drawing blood at 2-hours, 4-hours, and 6-hours at four to six hours after medication, would not be a big deal. However, we have to maximize our day to minimize client costs, and then things become stressful for us.
Ironic, because a normal amount of cortisol helps the body adapt in times of stress. So, we are using extra cortisol at the same time we are testing for too much. Cortisol also helps regulate proper body weight, tissue structure, skin condition, and other features of good health. Twenty minutes before we closed, the last sample was drawn. Shortly after we closed the serum was separated from the cells and refrigerated. Stephanie dealt with the lab, FedEx and overnight shipping on ice the next day.
A few days later and three conversations with the board-certified endocrinologist later, we had results. Although the three dogs had similar symptoms, they had very different results. Dixie is an older retriever mix. She was diagnosed with Cushing’s two weeks ago and has been started on medication to block part of her adrenal gland from producing cortisol. This was the 10-14 day post-treatment test. She had stopped having accidents in the house and was still eating very well. Her post ACTH cortisol was in the third category. We will continue her on the current dose, but carefully monitor her for recurrence of clinical signs.
Molly’s baseline cortisol was very high, but when given dexamethasone, the levels suppressed to normal levels or the first category. I am convinced that Molly has Cushing’s (based on clinical signs and lab work), but it is not progressed far enough to treat at this time. Because the body must have some cortisol to live, treating Molly at this time could be disastrous.
Hydi had been on medication for a while and had been doing reasonably well. Her results were in the fourth category. Although we could have continued to dispense medicine at the same dose, too much cortisol leads to heart, liver and kidney problems. The blood test proved that she needed to be on a higher dose of medicine. Although we discussed switching to twice a day medication, I think Hydi will do well on once a day. Her symptoms do not get worse in the evening but are generally not in control at the same level all of the time.
Hydi has a concurrent allergy problem, and as we get the cortisol levels under control, we will have to work harder on the allergy.
So, Dixie will continue on the same dose and get retested in three months. The owners will watch for signs. Molly will be retested in six months (no medicine) and because we changed her medicine Hydi will be retested in another two weeks.
On the internet, there will be many things about the different types of Cushing’s disease. Cushing’s is either caused by the pituitary (a tiny gland at the base of the brain that produces ACTH) which is pituitary-dependent or by an overactive adrenal gland or tumor which is adrenal-dependent. If the brain says produce too much or the adrenals just produce too much doesn’t matter the medication will block the production at the adrenal and therefore treat either.
Treating Cushing’s is definitely a balancing act. Too many meds and they have too little cortisol (Addison’s) and can die. Too few medicines and they still have Cushing’s and all the side effects fo the disease. Luckily medicated and controlled dogs with the disease can live a good life. They must be closely monitored by a veterinarian. The owner should be diligent about bringing the dog in for blood work and checkups, watching for side effects and giving the proper medication.