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Diabetes insipidus is a water problem, not a sugar problem. The pituitary gland either stops making the hormone that tells the kidneys to hold onto water, or the kidneys stop listening to it. Either way the dog produces huge volumes of very dilute urine and drinks constantly to keep up. It's uncommon, and in most dogs it's manageable for years.
Key Takeaways
Call us the same day if your dog is drinking heavily and is also vomiting, off food, weak, wobbly, disoriented or having seizures. Those signs point to a sodium problem or to one of the more serious causes of excessive thirst, and they need bloodwork today rather than an appointment next week. Call (519) 896-0532.
It's a failure of the body's water conservation system. A hormone called antidiuretic hormone, or ADH, is made in the hypothalamus and released from the pituitary gland at the base of the brain. Its job is to tell the kidneys to pull water back out of the urine before it leaves the body. When that signal fails, water keeps going out.
The result is urine that's barely more concentrated than tap water, in enormous quantities, and a dog who drinks constantly because he has to. The drinking is the compensation rather than the disease, and it's why most of these dogs stay reasonably well as long as the water bowl is full.
The two names get mixed up constantly. Diabetes mellitus is the common one, a disorder of sugar handling, and it's what people mean when they say their dog is diabetic. Diabetes insipidus has nothing to do with insulin or blood sugar. The two conditions share a name because both were historically diagnosed by tasting urine. Mellitus tasted sweet. Insipidus was insipid, meaning it tasted of nothing.
There are two versions and the difference decides the treatment. Central diabetes insipidus means the brain isn't producing enough ADH. Nephrogenic means the ADH is there but the kidneys can't respond to it.
| Central | Nephrogenic | |
|---|---|---|
| What's gone wrong | Pituitary or hypothalamus isn't releasing enough ADH | ADH is present, but the kidney tubules don't respond to it |
| Usual cause | Head trauma, a pituitary tumour, a cyst or granuloma, or no identifiable cause at all | Almost always another disease or a drug interfering with the kidney's response |
| Congenital form | Rare | Rare; the kidney's ADH receptors are absent or defective from birth |
| Response to desmopressin | Yes, urine concentrates | No meaningful response |
| Main treatment | Desmopressin, long term | Treat the underlying disease or stop the drug |
In practice the more useful split is congenital versus acquired. A dog born with defective kidney receptors is a genuine rarity, whereas one whose kidneys have stopped responding to ADH because of another illness is not, and that second group is what we're usually looking at when the urine won't concentrate.
Central diabetes insipidus follows damage to the pituitary or hypothalamus. Merck lists large pituitary tumours, an expanding cyst or granuloma, skull trauma, parasite migration, local infection, and pituitary surgery.1 In a fair number of dogs no cause is ever found, and the disease is simply managed as it presents.
Nephrogenic diabetes insipidus usually comes attached to something else. Merck's list of conditions that blunt the kidney's response to ADH includes electrolyte disturbances, bacterial toxins in the bloodstream, Cushing's disease, liver disease, kidney infection and leptospirosis, along with certain drugs.1 Corticosteroids are the drug most owners ask about, and if your dog is on long-term prednisone, increased drinking and urinating is an expected effect rather than a new disease.
Finding dilute urine is the easy part. What changes the plan is working out whether it's a pituitary problem, a kidney problem, or a side effect of a medication your dog is already taking.
Drinking and urinating, in volumes that are hard to ignore. Owners usually describe it before they describe anything else: the water bowl empties two or three times a day, the dog drinks from the toilet, the puddles outside are enormous.
Signs worth mentioning to us:
A dog leaking urine while asleep or lying down isn't polyuric, that's urinary incontinence, and a dog posturing repeatedly and producing almost nothing is straining. Both get described to us as "peeing a lot" and neither is this condition.
Measure the water before you come in. Fill the bowl with a measured amount, top it up with measured amounts, and record the 24 hour total. Then divide by your dog's weight in kilograms. Above 100 mL per kilogram per day is polydipsia by definition.2 That single number tells us more than any description.
By elimination, in stages, and the early stages are the ones that find the answer in most dogs.
Excessive drinking has a long list of causes and diabetes insipidus sits near the bottom of it. In dogs the three that turn up most often are chronic kidney disease, diabetes mellitus and hyperadrenocorticism, better known as Cushing's disease.2
So the first visit is bloodwork, a urinalysis and often a urine culture. That combination picks up diabetes mellitus, catches most cases of kidney disease, flags high blood calcium, points at liver disease, and can reveal a kidney infection. A urinalysis also tells us whether there's protein in the urine, which sends the workup in a different direction again. If the dog is an intact female, pyometra goes on the list too.
Urine concentration is the number we watch. In a dog with complete diabetes insipidus, specific gravity sits at or below 1.006, which is more dilute than blood. Partial cases run higher, somewhere between 1.008 and 1.020.1 In a UC Davis review of 20 dogs with central diabetes insipidus, dilute urine was a consistent finding.3
This test is done in hospital, and it is not a matter of taking the water away for a set number of hours. Water is withheld while we track body weight, urine output and urine concentration closely. The test stops at whichever of three endpoints arrives first: urine specific gravity above 1.025, a 5% loss of body weight, or daily water allowance below 60 mL/kg.1 In a dog who genuinely can't concentrate urine, that can happen quickly.
There's preparation beforehand too. Water is restricted gradually, by 5% to 10% a day over several days, to reverse the washout of the kidney's concentrating gradient that chronic overdrinking causes. Skip that step and the test can read positive in a dog who doesn't have the disease. Merck states plainly that abrupt withdrawal of water is not recommended, and the test isn't appropriate at all in a dog who is already dehydrated or has kidney disease.1
Please don't try any version of this at home. The monitoring is the whole test, and without it you're just dehydrating a dog who can't afford it.
This is the step that names the disease. Once the dog has concentrated as far as he's going to, desmopressin is given and urine specific gravity is measured again at set intervals, typically 4, 8, 12, 18 and 24 hours.1
A dog with central diabetes insipidus concentrates his urine, because we've supplied the hormone he was missing. A dog with nephrogenic diabetes insipidus doesn't change, because the hormone was never the problem. That contrast is what gives us the answer, and it's also why a desmopressin trial on its own is sometimes used as a gentler alternative to the full deprivation test.
Central diabetes insipidus is treated with desmopressin, a synthetic version of the missing hormone. It comes two ways. The nasal spray is given as drops into the conjunctival sac rather than up the nose, and the oral tablets are dosed at roughly 0.1 to 0.2 mg per dog every 8 to 12 hours.1 Most dogs settle onto a schedule of every 12 to 24 hours and stay on it for life.1
Nephrogenic diabetes insipidus is treated by dealing with whatever is causing it. If it's a drug, the drug gets reviewed. If it's an infection or an endocrine disease, that's the target. Desmopressin isn't the answer here, because the kidneys already can't hear the signal.
Thiazide diuretics are the other option, and they work in both forms. They cut urine output by 30% to 50% by reducing total body sodium, which contracts the fluid volume and means less water reaches the point where it would be lost.4 It sounds backwards to treat excessive urination with a diuretic, and it is, but the effect is real.
It depends almost entirely on the cause rather than on the diabetes insipidus itself. The water problem is the manageable part. Whatever is driving it sets the timeline.
Where no cause is ever found and the dog responds to desmopressin, he can do well for a long time on twice daily drops. Where a pituitary tumour is driving it, the outlook is set by that tumour: its type, its size, and whether it's pressing on anything else. When the trigger was head trauma, the disease is sometimes temporary. In one documented case a dog developed diabetes insipidus after being hit by a car. He started desmopressin on day two, came off it on day nine once his sodium normalised, and went home resolved on day thirteen.5
Not every case is complete, either. Of the 20 dogs in the UC Davis series, 7 had complete central diabetes insipidus and 13 had the partial form.3 Partial cases retain some hormone production, and they're often the easier ones to manage.
If your dog has been drinking more than usual for a few weeks, book the bloodwork and bring the water measurement with you. In most dogs we find something other than this. In the few where we don't, it's manageable.
No. Diabetes mellitus is a disorder of blood sugar and insulin, and it's what people mean when they say a dog is diabetic. Diabetes insipidus is a disorder of water handling, with normal blood sugar and no insulin involvement. They share a name for a historical reason: both used to be diagnosed by tasting urine. Mellitus tasted sweet, insipidus tasted of nothing. The treatments have nothing in common.
More than 100 mL per kilogram of body weight per day is polydipsia by definition, and most healthy dogs drink somewhere around 50 to 60 mL per kilogram. For a 20 kg dog that means roughly 2 litres a day is the threshold. Measuring is straightforward: fill the bowl with a measured amount, top it up with measured amounts, and record the 24 hour total. Bring that number to your appointment, because it's more useful than any description of how much your dog seems to be drinking.
No. This is the one thing not to do. A dog who can't concentrate his urine will keep losing water regardless of what he drinks, so removing the bowl causes rapid, dangerous dehydration and a rise in blood sodium. Water deprivation testing is done in hospital with close monitoring of weight and urine concentration, and it stops at set endpoints rather than running for a fixed number of hours. Water is also restricted gradually beforehand over several days, because abrupt withdrawal is not recommended.
By ruling out the common causes first. Excessive drinking has dozens of causes, and in dogs the usual three are chronic kidney disease, diabetes mellitus and Cushing's disease, all far more common than diabetes insipidus. So the workup starts with bloodwork, a urinalysis and often a urine culture. Urine specific gravity at or below 1.006 points toward diabetes insipidus. Confirming it takes a modified water deprivation test in hospital, followed by giving desmopressin and re-checking urine concentration. Dogs with the central form concentrate their urine in response. Dogs with the nephrogenic form don't.
Usually it's managed rather than cured, but there are exceptions. When head trauma is the trigger, the condition can be temporary. In one published case a dog developed diabetes insipidus after being hit by a car, started desmopressin on day two, came off it on day nine once his sodium normalised, and went home resolved on day thirteen. When the cause is a pituitary tumour or no identifiable cause at all, treatment is generally lifelong. Nephrogenic cases can resolve if the underlying disease or drug causing them is dealt with.
Not always. Treating central diabetes insipidus isn't necessary in every dog, provided he has free access to water at all times and you can live with the volume of urine. Plenty of owners choose treatment simply because the overnight trips outside and the accidents become unworkable, which is a reasonable basis for the decision. What isn't optional is the water. It stays available whether or not your dog is on medication.
It's set by the underlying cause rather than by the water problem itself. A dog with no identifiable cause who responds to desmopressin can do well for years. A dog whose disease is driven by a pituitary tumour has an outlook determined by that tumour's type and size. Severity varies too. In a UC Davis review of 20 dogs with central diabetes insipidus, 7 had the complete form and 13 had a partial form that retains some hormone production and is generally easier to manage.
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