by: Oliver Knesl BSc BSc(Hons) MSc BVSc MRCVS Nestle Purina Consultant Veterinarian
Diabetes is a general term, which refers to a variety of disorders that are characterized by an animal drinking and urinating excessively (polydipsia and polyuria). Two very distinct diseases fall under the diabetes umbrella, namely diabetes mellitus and Diabetes insipidus.
Diabetes insipidus is a disease in which antidiuretic hormone (ADH) is either deficient or ineffective. ADH deficiency (Central Diabetes Insipidus) can be caused by birth defects (congenital), trauma or neoplasia (cancer). ADH can be ineffective due to a number of different diseases altering the way an animals kidneys respond to normal quantities of ADH (Nephrogenic Diabetes Insipidus). ADH is the most important hormone for the control of water balance in the body, so the usual clinical signs of diabetes insipidus include excessive urinating with associated, compensatory, excessive drinking.
Diabetes mellitus on the other hand is caused by a deficiency of the hormone insulin. Insulin is required to allow glucose to be taken up by the various body tissues, with most tissues being dependent on insulin to fulfill this function. A lack of insulin is, therefore, associated with an increased blood glucose concentration. Four clinical signs are very characteristic of the disease, namely, excessive drinking, excessive urinating, weight loss and an increased appetite/excessive ingestion of food.
Both of these diseases are associated with increased water consumption and increased urination, so the first step in investigating them usually involves measuring how much water the dog is actually drinking over a 24 hour period, together with a series of urine sample tests. A normal dog, at rest, will consume about 60ml/kg of water per 24 hours. Dogs drinking more than 100ml/kg per 24 hours are likely to have an underlying problem that needs to be investigated. Analyzing a urine sample helps a veterinarian to determine if the animals' kidneys are forming urine appropriately and if there is any evidence of disease or infection. Animals with diabetes insipidus often have an inappropriately dilute urine sample while dogs with untreated diabetes mellitus usually have glucose in the urine.
Blood tests are an important part of investigating the diabetes syndrome and need to be interpreted in the light of the animals clinical signs, water consumption and urine test results.
Diabetes mellitus tends to occur in middle aged to older dogs, with female dogs being at higher risk than males. A number of breed predispositions have been recognized including Poodles, Samoyeds, Miniature Schnauzers, Pugs, Daschunds and Beagles. Familial predispositions, those occurring in related groups of animals, have been reported in Keeshonds, Samoyeds, Minature Poodles and Rottweilers.
The treatment regimen for dogs with diabetes mellitus includes daily insulin injections, changes in diet and exercise, as well as the correction of obesity if present.<>There are numerous potential causes of excessive drinking and urinating in dogs with central diabetes insipidus being one of the least common. As a result, it is important for a veterinarian to rule out the other potential causes before focussing on central diabetes insipidus. Inherited forms of diabetes insipidus associated with birth defects leading to inadequate production of ADH hormone or decreased kidney responsiveness to ADH are extremely rare with very few reports of the condition in the veterinary literature. No apparent breed, sex or age predilections have been reported.
The kidneys ability to respond to ADH can, however be affected by a number of more common diseases (including kidney disease, liver disease, pyometra, etc) as well as by various drugs. Once the other more common conditions have been ruled out, a very specific diagnostic test (the modified water deprivation test) can be performed to help determine if diabetes insipidus is, indeed, the cause of the animals excessive drinking and urinating. Therapeutic options for animals suffering from diabetes insipidus include supplementation of a synthetic form of ADH.
Nelson, R. W. and Couto, C.G. (Eds). 2003. Small Animal Internal Medicine. 3rd Edition . Mosby, St. Louis. Feldman E.C. and Nelson R.W. (Eds) 2004. Canine and Feline Endocrinology and Reproduction. 3rd Edition . Saunders, Missouri.