Why Cushing’s Is So Easy to Confuse
The classic signs of Cushing’s disease — drinking and urinating more, a bigger appetite, a pot-bellied look, panting, and thinning hair — are strikingly non-specific. Each of them can be caused by several other common conditions in older dogs. That overlap is exactly why Cushing’s is both over-suspected and, at times, missed: the picture looks like Cushing’s, but the cause is something else entirely.
This is not a reason to self-diagnose from a symptom list. It is a reason to understand why your veterinarian insists on testing rather than treating based on signs alone. Here are the main conditions that wear the same disguise.
Diabetes Mellitus
Diabetes mellitus (DM) shares Cushing’s three most noticeable signs: dramatically increased thirst and urination, along with increased appetite. (These signs that are common to both Cushing’s and DM are known as the “three P’s”: polyuria (excess urination), polydipsia (excess drinking) and polyphagia (excess eating).) DM and Cushing’s can even coexist (and often do), because the excess cortisol of Cushing’s promotes insulin resistance and can make diabetes harder to control. Bloodwork and urine testing that show persistently high glucose point toward diabetes, and a dog with poorly controlled diabetes needs that addressed in conjunction with treatment of Cushing’s syndrome.
Hypothyroidism
An underactive thyroid produces some of the same skin and coat changes as Cushing’s — symmetrical hair loss, a dull coat, and skin problems — and it, too, is a disease of middle-aged and older dogs. The distinguishing features often go the other way on energy and weight: hypothyroid dogs tend to be sluggish and gain weight, and they usually do not have the marked thirst and urination that define Cushing’s. A thyroid panel helps separate the two.
Kidney Disease
Chronic kidney disease is another major cause of increased thirst and urination in senior dogs. Because kidney disease can also alter the results of adrenal-function tests, it is an important condition to identify first. Bloodwork and urinalysis assessing kidney values and urine concentration help distinguish it — and its presence changes which Cushing’s test a vet will choose.
Diabetes Insipidus and Liver Disease
Less common but worth naming: diabetes insipidus (unrelated to sugar diabetes) causes profound thirst and urination through a problem with water regulation, and certain liver diseases can raise the same liver enzyme, ALP, that is often elevated in Cushing’s. Both can nudge an inexperienced eye toward a Cushing’s diagnosis that the numbers do not actually support.
Why the Testing Matters — and Why It Is Careful
Here is the crucial point for owners: the screening tests for Cushing’s (the low-dose dexamethasone suppression test and the ACTH stimulation test) are prone to false positives when another illness with similar signs is present. A sick dog with kidney disease or uncontrolled diabetes can “test positive” for Cushing’s when it does not have it. This is why the veterinary guidelines emphasize testing only dogs whose clinical picture genuinely fits, and why your vet may treat or rule out other conditions first.
In practice, a good workup starts with the clinical signs, adds a baseline database (routine bloodwork and urinalysis) to look for supporting clues and rule out mimics, and only then moves to a specific Cushing’s screening test. Skipping steps is how dogs end up on cortisol-lowering medication they never needed.
The Bottom Line
Cushing’s syndrome (including Cushing’s disease) shares some or many of its signature signs with diabetes, hypothyroidism, kidney disease, and others — and the tests used to confirm it can be misleading if one of those conditions is present. If your dog is showing the classic signs, that is a reason to see your veterinarian for a proper, stepwise workup, not a reason to assume the diagnosis. Getting the right answer is what makes the right treatment possible.
Sources
- Merck Veterinary Manual — Cushing Disease (Pituitary-Dependent Hyperadrenocorticism) in Animals. merckvetmanual.com
- MSD Veterinary Manual — Endocrine Diseases in Animals. msdvetmanual.com
- Behrend EN, et al. “Diagnosis of Spontaneous Canine Hyperadrenocorticism: 2012 ACVIM Consensus Statement.” J Vet Intern Med. 2013. onlinelibrary.wiley.com
- BluePearl Pet Hospital — Cushing’s Disease (Hyperadrenocorticism). bluepearlvet.com
