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Diabetes Mellitus is a disease by which the islet cells of the pancreas (cells responsible for secreting the hormone insulin into systemic circulation) lack the ability to secrete adequate amounts of insulin, or, insulin receptors on body cells are refractory to the effects of insulin when secreted, or both. Insulin plays an important role in the body regulating blood sugar (glucose) in response to ingestion of carbohydrates. When blood glucose levels spike in the blood following a carbohydrate rich meal, insulin is secreted by the pancreas to trigger the body cells to take up the excess blood glucose out of systemic circulation. This keeps blood glucose levels in check, while providing glucose for the cells, which is their primary source of energy. When insulin is deficient from defective pancreatic islet cells, or, if body cell receptors are refractory to the effects of insulin, the result is chronically high blood glucose, diabetes mellitus.

The physiological effects of this disease are many. First, since body cells are not effectively taking up glucose, they are depleted of glucose and starved for energy. Over time, this leads to cell death and profound weightloss. Second, the excess blood glucose causes physiological problems. Excess glucose ends up passing through the kidneys and gets urinated out. Glucose attracts water, and therefore pulls excess water out of the body, causing chronic dehydration. This is the reason many diabetic dogs and cats drink excessive amounts of water. When the glucose rich urine collects in the urinary bladder, lower urinary tract infections often occur, because bacteria are attracted to the glucose.

In the brain, with individual cells that make up brain tissue, called neurons, being especially sensitive to the inability to take up glucose for energy, cells become compromised and begin to die. In combination with high levels of blood glucose that occur with diabetes mellitus and osmotic and electrolyte disturbances that result from this, disorientation, seizure, coma, and even brain death can occur in unregulated canine and feline diabetics.

At the level of the blood vessels, inflammatory disease of the walls of the blood vessels can occur in cases of unregulated diabetes called vasculitis. Vasculitis may lead to disturbances in circulation, vascular pain, and clot formations.

Brain is not the only central nervous system component that may be harmed by diabetes. Peripheral nerves may also be adversely affected by unregulated diabetes as high levels of blood glucose can lead to inflammation of these nerves, a condition known as neuropathy, a potentially painful and debilitating consequence.

Finally, high blood glucose leads to metabolic disturbances of the lenses of the eyes leading to cataracts. This is an especially prevalent result of diabetes in dogs, which can severely compormise their vision.

Diagnosis is obtained through blood test and urinalysis. On general chemistry, high blood glucose is hallmark for diabetes mellitus and there are often concurrent electrolyte disturbances. On urinalysis, glucose is often found in the urine, which is never normal and clearly indicative of diabetes. Often, concurrent urinary tract infections are also discovered.

In consideration for treatment, there are significant differences in management of the diabetic cat versus the diabetic dog. With dogs being far more sensitive to the adverse effects of high blood glucose (vascular disease, peripheral nerve disease, cataracts, etc.), like people, it is important to try to regulate them as tightly as possible. With cats, on the other hand, since they are as a species more resistant to the advserse effects of high blood glucose, and given that stress (such as that cause by being in a veterinary clinic…) can have profound influence on blood glucose levels in cats, a more loosely regulated approach is favored. In fact, as a general rule in the veterinary profession, we have found ourselves having sometimes in the past caused more problems trying to regulate cats too tightly, than the problems caused by the diabetes itself. Therefore, our approach to regulating diabetes in each species is quite different. Let us begin with management of diabetes in the canine.

In dogs, there are several choices for types of insulin to choose from. My top choice is a human based insulin called NPH, as it is reasonably priced, can be obtained easily at any human pharmacy, and has shown itself to be as effective and consistent as any other insulin on the market for dogs in my experience.

When first treating a diabetic dog with insulin, it is important to be mindful that the response to insulin is very individual, with a huge variation in blood glucose from one patient to the next from a given insulin dose. For this reason it is difficult to impossible to predict the proper insulin dose without doing what is called a blood glucose curve. This is when a conservative dose of insulin is administered, and the blood glucose levels are measured once every two to three hours. The insulin dose is adjusted according to these readings, and the patient is sent home on the appropriate dose, which is typically arrived at within 2-4 days in hospital.

Following the intitial blood glucose curve, I typically follow up with a fructosamine level in 3 weeks. This gauges the body’s average response to insulin over a 3 week period. This is a more hands off method to monitor the blood glucose than a curve and is appropriate at this stage. The insulin dose is adjusted accordingly and the fructosamine is repeated every three weeks until adequate regulation is achieved. Once proper regulation is obtained, I typically have the patient come in once every 6 months for follow up fructosamine analysis, as well as weigh the dog and get updates from the owner as to water intake and urine output.

With cats, the initial response to a given insulin dose is also individual and arriving at the right dose can be challenging at first, just like in dogs. However, given the profound spike in blood glucose that can occur from stress in cats, keeping them in the hospital for a glucose curve is not accurate and ill-advised from my view. A more hands off approach is favored.

Regarding the choice of insulin for cats, there are two main options current being favored for cats in veterinary medicine, and both are quite good: PZI and Lantus. Either choice is good, but I tend to favor Lantus, as I find it is more likely to send a diabetic cat into diabetic remission (see below) in my experience, it is a human based insulin and therefore easily attainable, and it generally costs a bit less than PZI.

My method for regulating cats (which is appropriate with either PZI or Lantus) is to have the owners start with a conservative insulin dose of 0.5 Units per kg of body weight, two times daily. I then have the cat return in one week for a quick blood glucose test, timed to be performed about 12 hours following the morning insulin injection. Good regulation would be blood glucose falling between 300-350. If the number does not fall within this range, then the insulin dose is adjusted and a blood glucose test is repeated in this fashion in one week…and so on and so forth until regulation is achieved. Once regulation is achieved, then a 12 hour post morning insulin injection blood glucose test is performed once every 3 months. Patient’s weight is also closely monitored, as are clinical updates from the owner.

The prognosis for diabetes mellitus is typically good with reasonably good owner compliance, as well as the absence of other complicating systemic disease. In cats, some diabetic can go into what is called diabetic remission, where the body becomes increasingly less dependent on insulin until it is no longer needed. As previously mentioned, Lantus insulin seems to lead to remission in cats more than the other types of insulin available for use in cats. Dietary concerns are also important for diabetic cats. An ultra low carb diet gives the best opportunity to optimally regulate diabetic cats, while also increasing their likelihood of remission.

I do not like low carb in dogs, however, as it seems to cause more trouble than benefit. Instead, I favor diets that are well balanced and carbohydrate controlled, where sugar is derived minimally from simple carbohydrates and more from complex carbs.

The most common complication and potentially dangerous event for diabetics, is what is known as a diabetic crash. This sometimes occurs for no apparent reason following the normal administration and dose of insulin, however, factors that prevent the patient from eating normal amounts on a given day can make the typically normal amount of insulin excessive, leading to a dangerous drop in blood glucose. For this reason, it is ideal to time two tiems daily meals around the insulin injections. This can be a bit more challenging in cats than in dogs, as many cats prefer to graze on freely offered food rather than have discrete meals.

The consequences of such a sudden drop in blood sugar can range from lethargy and weakness, to seizure, coma, and even death. For this reason, it is advisable that owners of diabetic dogs and cats have at their disposal, sugary syrup, such as maple syrup or karo syrup. If diabetic crash is suspected, the owner should rub a generous amount of one of these sweet syrups onto the gums to quickly raise the blood glucose level, and get the patient to a vet as soon as possible.


Roger L. Welton, DVM
Founder and Chief Editor,
President, Maybeck Animal Hospital

Article updated 10/1/2012

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