Cushing Syndrome In Dogs

Understanding Cushing Syndrome In Dogs

Cushing's syndrome in dogs is a hormonal disorder caused by prolonged exposure to high levels of cortisol. The technical term is hyperadrenocorticism, and it comes in a few different flavors. Most cases are pituitary-dependent, meaning a benign tumor on the pituitary gland is pumping out too much ACTH, which then tells the adrenal glands to overproduce cortisol. A smaller percentage comes from an adrenal tumor itself, and then there's iatrogenic Cushing's, which happens when a dog has been on long-term steroid medication. The symptoms overlap with a bunch of other common conditions, which is exactly why so many dogs get misdiagnosed or diagnosed late. Polyuria, polydipsia, polyphagia — increased urination, drinking, and appetite. Pot-bellied appearance. Thin skin. Hair loss that's usually symmetrical. Lethargy. These are all classic signs, but they're also signs of diabetes, hypothyroidism, kidney disease, and a handful of other things. Your vet should be running bloodwork and urine tests before jumping to any conclusions.

Diagnosing Cushing Syndrome In Dogs

There's no single test that confirms Cushing's. You need a combination approach. The first screening test most vets run is a low-dose dexamethasone suppression test, or LDDST. You draw a baseline cortisol, give dexamethasone, then draw again at 4 and 8 hours. In a healthy dog, the dexamethasone should suppress cortisol production. In a Cushing's dog, it won't. But here's the thing that trips people up — the LDDST can give false positives. Liver disease, diabetes, and certain medications can mess with the results. A negative result basically rules it out, but a positive result just means you need to keep looking. Another common test is the adrenocorticotropic hormone, or ACTH stimulation test. You draw baseline cortisol, inject synthetic ACTH, wait two hours, and draw again. Dogs with Cushing's typically show an exaggerated cortisol response. This test is better at confirming hyperadrenocorticism once you already suspect it, but it's not great at distinguishing between the different types. For that, you need high-dose dexamethasone suppression testing or an adrenal CT scan. I've seen too many cases where a vet runs one test, gets a borderline result, and calls it Cushing's. Don't let that happen. If the clinical signs aren't a strong match, or if the test results are ambiguous, push for a second opinion or additional testing. The cost adds up, sure, but treating a dog for Cushing's when they don't have it is worse.

Treatment Options and What to Expect

Trilostane, sold under the brand name Vetoryl, is the go-to medication for most cases. It works by inhibiting the enzyme 3-beta-hydroxysteroid dehydrogenase, which is involved in cortisol synthesis. Essentially, it blocks the adrenal glands from making as much cortisol. The typical starting dose is around 2.0 mg per kilogram of body weight, given once daily with food. But doses vary enormously between individual dogs. Some respond at 1 mg/kg, others need 5 or more. There's no universal formula. Mitotane, also known as Lysodren, is the older alternative. It's actually aDDT derivative that selectively destroys the adrenal cortex. It's effective, but the therapeutic window is narrower and the side effects can be more severe. Gastrointestinal issues, lethargy, and in worst-case scenarios, Addisonian crisis — a life-threatening cortisol deficiency — are real risks. Many vets prefer trilostane these days because it's generally easier to manage. But in some cases, particularly when trilostane isn't available or isn't working, mitotane still has a place. Monitoring is non-negotiable. After starting treatment, you need to do an ACTH stimulation test around 10 to 14 days in to check cortisol response and adjust the dose. After that, recheck every 3 to 6 months for the rest of the dog's life. The goal isn't to normalize cortisol completely — that's actually dangerous. You want to bring it down to a mid-normal range. If you suppress it too far, you're effectively putting the dog into iatrogenic hypoadrenocorticism, which is essentially the same as Addison's disease and can be fatal.

I had a case last year where a dog was being treated with trilostane and the owner reported the dog seemed fine. No extra water consumption, appetite was normal, energy was back. Great, right? Wrong. The ACTH stim test showed a cortisol level that was borderline low-normal. I increased the frequency from once daily to twice daily dosing and the cortisol came back to a healthier mid-range. The dog had been under-treated the whole time, and the owner didn't notice because the clinical signs had improved enough. This is why you can't rely on symptoms alone. You need the bloodwork.

Common Pitfalls and Complications

One of the biggest issues with treating Cushing's is that the underlying cause matters. If it's a pituitary macroadenoma — a large tumor on the pituitary — medical management might control the cortisol levels, but it won't address the tumor itself. Large pituitary tumors can press on surrounding brain structures and cause neurological symptoms. Signs include seizures, changed behavior, blindness, or head pressing. In these cases, radiation therapy or surgical intervention might be necessary, and medical management alone won't cut it. Adrenal tumors are another different story. If the Cushing's is caused by a malignant adrenal tumor, surgery to remove the affected adrenal gland is theoretically the best option. But adrenal tumor removal is a high-risk procedure. The adrenal glands sit right next to the caudal vena cava, and these tumors can invade that vessel. Mortality rates for adrenalectomy hover around 10 to 15 percent in the best hands. Plus, if the tumor has metastasized, which happens in roughly half of malignant cases, surgery is pointless. A CT scan before any surgical consideration is essential. There's also the issue of concurrent conditions. Dogs with Cushing's frequently develop diabetes mellitus, urinary tract infections, pancreatitis, and hypertension. Treating the Cushing's often improves these secondary conditions, but sometimes they need independent management too. I've seen diabetic Cushing's dogs where getting the cortisol under control was the key to finally getting the blood sugar stable. Insulin requirements dropped significantly once the hyperadrenocorticism was managed.

Another thing people don't talk about enough is the quality of life trade-off. Yes, treatment can extend lifespan. Studies show that treated Cushing's dogs live longer than untreated ones. But these dogs are on lifelong medication with regular blood tests and dose adjustments. Some owners find the burden of management too much, especially as other age-related conditions start showing up. There's no shame in that decision. It's a serious chronic condition, and the treatment isn't harmless.

What Owners Should Actually Know

If your dog has been diagnosed with Cushing's, here's the practical stuff. Give the medication exactly as prescribed, with food. Missing doses or giving them on an empty stomach can cause cortisol crashes. Watch for signs of over-suppression — vomiting, diarrhea, lethargy, weakness, loss of appetite. If you see these, contact your vet immediately. They may need to hold a dose or reduce the amount. Keep a diary. Track water intake, urination frequency, appetite, energy level, and any side effects. This gives you and your vet actual data between appointments. Most owners think they're remembering everything, but they're not. A notebook or a simple phone note makes a real difference during those 3-month rechecks. Don't skip the monitoring appointments. I can't stress this enough. The whole treatment framework falls apart without regular ACTH stimulation tests. Doses drift over time. Dogs gain or lose weight. Their adrenal responsiveness changes. A dog that was stable on a certain dose six months ago might be over-suppressed now, or under-suppressed, and you wouldn't know without the test.

Life expectancy varies widely. With proper treatment, many dogs live two to three years or more with a decent quality of life. Some live longer. The prognosis is worse if there's an underlying malignant adrenal tumor or a large pituitary mass causing neurological issues. Untreated Cushing's typically shortens lifespan significantly, and the quality of life deteriorates as secondary complications take hold. There's no cure, but there is management. It's not straightforward, and it's not cheap, but for most dogs and owners, it's worth it. The alternative is watching a dog slowly get worse over months or years — more thirst, more accidents in the house, muscle wasting, recurrent infections, and eventually organ failure. Treatment takes the edge off all of that. It doesn't fix the problem, but it buys time and comfort. That's usually enough.