Cushing's disease is the most common endocrine disorder in older dogs, and it is one of the easiest to overlook. The classic picture — a thirsty dog with a pot-bellied silhouette and thinning hair — develops so slowly that owners often chalk it up to "just getting old." By the time the diagnosis is made, the dog has frequently been losing quality of life for a year or more. This guide explains what Cushing's actually is, who is at greatest risk, the warning signs every owner should know, and what modern treatment looks like.
What Cushing's Disease Actually Is
Cushing's disease — formally called hyperadrenocorticism — is a condition in which the body produces too much cortisol, the stress hormone. Cortisol is essential in normal amounts: it regulates blood sugar, blood pressure, the immune response, and the body's reaction to inflammation. In excess, however, it begins to dismantle the very tissues it normally protects, weakening skin, muscle, ligaments, and the immune system over months and years.
There are three forms of the disease, and the distinction matters because treatment differs. Pituitary-dependent hyperadrenocorticism (PDH) accounts for roughly 80–85% of natural cases. A small benign tumor in the pituitary gland at the base of the brain over-secretes ACTH, the hormone that tells the adrenal glands to produce cortisol. Adrenal-dependent hyperadrenocorticism (ADH) makes up most of the rest, caused by a tumor on one of the adrenal glands themselves; about half of these tumors are malignant. The third form is iatrogenic Cushing's, caused by long-term administration of steroid medications such as prednisone — the only form that can sometimes be reversed by carefully tapering the offending drug.
Which Dogs Are at Highest Risk
Cushing's almost always shows up in middle-aged to senior dogs, with most diagnoses occurring after age seven. Pituitary-dependent disease is strongly biased toward smaller breeds. Cornell University and the Merck Veterinary Manual list Miniature Poodles, Dachshunds, Boxers, Boston Terriers, Yorkshire Terriers, Bichon Frises, Staffordshire Bull Terriers, and Miniature Schnauzers among the most over-represented breeds. Adrenal-dependent disease tends to favor larger dogs — German Shepherds and Labrador Retrievers in particular — and is more common in females.
Because the early signs of Cushing's overlap with normal canine aging — drinking a bit more, sleeping a bit more, putting on weight around the middle — small-breed seniors are frequently the patients in whom the diagnosis is delayed the longest. If you live with a Mini Schnauzer, a Yorkie, a Dachshund, or a Boston Terrier over the age of eight, the threshold for asking your vet "could this be Cushing's?" should be low.
Warning Signs Owners Should Watch For
Cushing's typically announces itself through a recognizable cluster of changes, all driven by chronically elevated cortisol. The most common signs include:
- Increased thirst (polydipsia) — owners often notice the water bowl emptying twice as fast as it used to.
- Increased urination (polyuria) — more frequent trips outside, larger puddles, and sometimes new house-training accidents in a previously reliable adult dog.
- Increased appetite (polyphagia) — a ravenous, food-obsessed dog that begs and steals in a way it never used to.
- Pot-bellied appearance — caused by liver enlargement, fat redistribution, and weakening of the abdominal muscles.
- Hair loss — usually symmetrical, sparing the head and legs, with a dull, dry coat that doesn't grow back after clipping.
- Thin, fragile skin with prominent veins, dark patches (hyperpigmentation), and chalky calcium deposits called calcinosis cutis.
- Persistent panting, especially at rest or overnight.
- Recurrent skin and urinary tract infections, because cortisol suppresses the immune system.
- Muscle weakness — difficulty jumping into the car or onto the couch.
Few dogs show every sign at once. The combination most owners notice first is thirsty, hungry, and pot-bellied — a dog drinking from puddles, draining the bowl overnight, and rounding out around the middle despite no change in diet. Any one of those changes deserves a vet visit; together, they should trigger testing.
How Cushing's Is Diagnosed
There is no single "Cushing's test." The 2012 American College of Veterinary Internal Medicine (ACVIM) consensus statement explicitly warns against testing dogs that don't have suggestive clinical signs — false positives are common, especially in animals that are sick or stressed for unrelated reasons. The diagnosis proceeds in stages.
The workup usually starts with a complete blood count, chemistry panel, and urinalysis. Classic findings include a markedly elevated alkaline phosphatase (ALP), dilute urine, and sometimes mild changes in cholesterol and liver enzymes. A urine cortisol-to-creatinine ratio is sometimes used as a screening test: a normal result helps rule the disease out, but an abnormal result is not by itself diagnostic.
To confirm the diagnosis, vets rely on one of two dynamic tests. The low-dose dexamethasone suppression test (LDDST) is widely considered the most accurate confirmatory test in dogs, while the ACTH stimulation test is faster and more practical in some clinics — and is the only test that can diagnose iatrogenic Cushing's. Each has trade-offs in sensitivity and specificity, and your vet's choice often depends on how the dog is presenting.
Once Cushing's is confirmed, the next question is whether it is pituitary or adrenal in origin. Abdominal ultrasound is the workhorse here: it lets the vet evaluate adrenal size and shape and look for a mass on one gland. In ambiguous cases, an endogenous ACTH measurement or advanced imaging (CT or MRI of the pituitary) may be needed.
Modern Treatment: What Actually Helps
For pituitary-dependent disease and most adrenal tumors that cannot be safely removed, the cornerstone of treatment is daily oral medication. The only drug currently approved by the U.S. FDA for both forms of canine Cushing's is trilostane (sold as Vetoryl). Trilostane works by competitively inhibiting an enzyme called 3β-hydroxysteroid dehydrogenase, which the adrenal glands need in order to manufacture cortisol. Lowering the supply of cortisol relieves the symptoms while leaving the underlying tumor in place.
The label starting dose is 2.2 to 6.7 mg/kg once daily, but a growing body of evidence — including a 2022 study in the Veterinary Record — supports starting at the lower end of that range and using twice-daily dosing for many dogs, which produces smoother cortisol control with fewer peaks and troughs. Close monitoring is essential. AAHA and most internal-medicine specialists recommend rechecking the dog around 10–14 days and again at 30 days after starting or adjusting therapy, then every three months once stable. Clinical response — water intake returning to normal, appetite normalizing, hair regrowing — is at least as important as bloodwork numbers.
The main risk of trilostane is over-suppression, in which cortisol falls too low and the dog becomes weak, vomits, or develops a true Addisonian (hypoadrenocortical) crisis. Owners should be coached to stop the medication and call the vet immediately if their dog stops eating, vomits, becomes lethargic, or develops diarrhea. With careful monitoring, life-threatening complications are uncommon.
An older alternative, mitotane (Lysodren), is still used in some practices. It selectively destroys cortisol-producing adrenal cells and can be effective, but it requires a more complex induction protocol and carries a higher risk of permanent adrenal damage. For dogs with a single resectable adrenal tumor, surgical adrenalectomy can be curative when performed by an experienced surgeon. Radiation therapy is sometimes used for large pituitary tumors that are causing neurological signs.
Long-Term Outlook and Quality of Life
Cushing's is rarely cured, but it is very manageable. Treated dogs with pituitary-dependent disease commonly live two to four more years, and many live longer; quality of life improves dramatically within weeks of starting effective therapy as thirst, appetite, and energy normalize. The hair coat usually takes longer — three to six months for visible regrowth is typical.
Untreated Cushing's is a different story. Sustained high cortisol predisposes dogs to several serious complications, including diabetes mellitus, high blood pressure, recurrent infections, pulmonary thromboembolism, and pancreatitis. Treating the underlying disease reduces — though does not eliminate — the risk of all of these. For owners weighing whether to pursue treatment in a senior dog, the practical answer is almost always yes: the goal is a comfortable, alert, normally-thirsty dog rather than aggressive cortisol numbers, and trilostane delivers that for most patients.
What You Can Do Right Now
If you live with a small-breed senior dog, learn the cluster: thirsty, hungry, pot-bellied, thinning coat. Watch the water bowl. Notice if your dog suddenly cannot wait through the night to go out. If two or more of these changes are present, ask your vet specifically about screening for Cushing's — and be ready for a multi-step workup rather than a single answer. Catching the disease earlier means starting treatment before complications stack up, and it gives your dog the best chance at the comfortable, energetic later years they deserve.