Posted on March 4, 2012
A Primer on Diabetes Insipidus
Mention the word diabetes, and one thinks of insulin injections and blood sugar levels. This is because diabetes mellitus (aka, sugar diabetes) is so darned prevalent in people, dogs, and cats. But did you know that there is another version of diabetes, one that has absolutely no impact on blood sugar levels? It is called diabetes insipidus (DI). This form of diabetes is far less common, but as it happens, I diagnosed two patients (one dog and one cat) with DI within the last week. Go figure! As things tend to happen in “threes” I expect my third patient with DI will walk through the door next week!
Diabetes insipudus occurs when the kidneys are unable to conserve water. Under normal circumstances, the kidneys retain some of the water within the bloodstream for use within the body while eliminating the rest within the urine. This nifty little water conservation system is controlled by a hormone called vasopressin (aka, ADH or antidiuretic hormone). Vasopressin is produced within the brain’s hypothalamus. It is then stored and released from the pituitary gland, also within the brain. Now here’s the really cool part. There are sensors in the body that control exactly how much vasopressin is released into the blood stream after detecting exactly how much water the body needs. For example, if you are hiking in Death Valley and it is 110 degrees, your pituitary gland will release lots of vasopressin so that you produce minimal urine. Likewise, if you’ve just chugged a gallon of water, vasopressin release will be turned off thereby allowing your kidneys to “turn on the faucets.”
Diabetes insipidus occurs when vasopression is no longer released from the pituitary gland. Affected dogs and cats produce copious volumes of urine, and all that water loss results in profound thirst. Their dilute urine looks more like water than urine. In addition, affected animals are prone to urinary accidents, saturation of their litter boxes on a daily basis, and the inability to make it through the night without urinating. Under such circumstances, people are sometimes tempted to restrict their pet’s water intake. This can be disastrous- even with water withheld, massive amounts of urine will continue to be produced and the animal will quickly become dehydrated. Fortunately, most animals with DI who are deprived of water will drive their humans crazy until they relent and fill the water bowl.
The diagnosis or DI is made by first ruling out other diseases that can cause increased thirst and urine output including: kidney disease, liver disease, urinary tract infections, diabetes mellitus and other hormonal imbalances. The diagnosis is then confirmed based on a positive response to vasopressin therapy.
Trauma, infection, and cancer affecting the region of the hypothalamus/pituitary gland are all potential causes of DI. However, most cases of DI turn out to be idiopathic (an underlying cause cannot be determined). If your dog or cat has DI, your veterinarian will want to perform a thorough neurological examination. If neurological abnormalities are detected, a brain scan (MRI or CT) and collection of spinal fluid for analysis may be recommended.
The treatment for DI is vasopressin replacement therapy. This hormone is available in tablet and nasal spray formulations. The nasal spray must be fitted with an adaptive nozzle that allows application of the liquid as eye drops. Typically, marked reduction in water intake and urine output are observed within a few days to a week after beginning therapy. Other than the need to give daily, lifelong medication, the major drawback of treatment is that vasopressin is pretty darned pricey. It definitely pays to shop around at a number of pharmacies to obtain the best price. Barring no significant underlying brain disease, the prognosis for a patient with DI is excellent, and that’s definitely something that we internists don’t get to say frequently enough!
Have you any experience with diabetes insipidus? If so, please share what you know.
Nancy Kay, DVM
Diplomate, American College of Veterinary Internal Medicine
Author of Speaking for Spot: Be the Advocate Your Dog Needs to Live a Happy, Healthy, Longer Life
Author of Your Dog’s Best Health: A Dozen Reasonable Things to Expect From Your Vet
Recipient, Leo K. Bustad Companion Animal Veterinarian of the Year Award
Recipient, American Animal Hospital Association Animal Welfare and Humane Ethics Award
Recipient, Dog Writers Association of America Award for Best Blog
Recipient, Eukanuba Canine Health Award
Recipient, AKC Club Publication Excellence Award
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Please visit http://www.speakingforspot.com to read excerpts from Speaking for Spot and Your Dog’s Best Health. There you will also find “Advocacy Aids”- helpful health forms you can download and use for your own dog, and a collection of published articles on advocating for your pet’s health. Speaking for Spot and Your Dog’s Best Health are available at www.speakingforspot.com, Amazon.com, local bookstores, and your favorite online book seller.