DIABETES MELLITUS IN DOGS AND CATS

Diabetes in the dog and cat and the treatment for diabetes mellitus are interesting and challenging topics.  Diabetes mellitus (DM) is a disorder where the body is unable to regulate blood sugar levels.  (There is another dissimilar disease called Diabetes Insipidus that is associated with pituitary gland dysfunction.)  Each case seems to be different, and regulating the diabetic dog or cat so that their blood glucose levels are as normal as possible can be a challenge. Cats present unique challenges due to their small body size and narrow range of insulin needed to control blood glucose levels. Learn more about dietary influences on diabetes in cats here.  The ultimate problem with a diabetic dog or cat is that even in the presence of sugar (glucose) in the blood stream, something interferes with the entry of that sugar into the body's cells where it is required for the life sustaining energy of those cells.  With no sugar (glycogen) in the cells, the cell dies in a very short period of time; with decreased sugar the cell cannot function optimally.

A highly complicated disease entity, diabetes has been classified according to what pathway of energy metabolism has been disrupted.  Fortunately with diabetes mellitus in dogs and cats most cases can be managed successfully with insulin injections and dietary modification. There are several brands of insulin available to veterinarians and your veterinarian may suggest or favor one brand rather than another.  Cats often are managed by use of a PZI (protamine zinc) insulin preparation.  Do not be bashful with your dog or cat's veterinarian if you do not understand the how, why, and when of managing diabetes in your dog or cat.

TYPES OF DIABETES MELLITUS (DM) IN DOGS AND CATS
Type I... Occurs when very little or no insulin is produced. In these cases, insulin must be administered by injection.  Most diabetic dogs have what is termed "insulin dependent" diabetes. This means that insulin from an external source (injections of insulin) will be required for the dog's survival; dietary modification alone won't stabilize the blood sugar level.

CAUSE
In dogs... The cause is considered in most cases to be due to damage to the cells in the pancreas (called beta cells or islet cells) that produce insulin.  Often the damage is due to an abnormal self-destruction of the cells by the body's own immune system actions.  This is termed "auto-immune destruction" or "immune mediated" damage. 

In cats... The most common causes of diabetes in cats are obesity, pancreatitis, or immune mediated damage of the pancreatic beta cells.  There has recent research demonstrating the connection between obesity in cats and the rish

Type II... Very rarely occurs in dogs and cats. In this type of diabetes the patient may be producing insulin but for various reasons the cells are not able to respond to the presence of insulin-glucose at the cell wall so that glucose carrying molecules are unable to enter the cells... so the energy from glucose is not available to the cell.  This is termed "insulin resistance".  The insulin is present but the cells are resistant to its vital effects in transporting glucose into the cell.

Transient DM... This occurs most often in cats where diabetic signs are variable.  Some diabetic cats may even have periods where they no longer need insulin injections. These periods are unpredictable and blood sugar level tests may need to be done routinely and the cat watched closely for signs of reoccurring diabetes.

SIGNS OF DIABETES MELLITUS
Typical signs of diabetes mellitus in dogs and cats include excess water consumption and excess urination, increased appetite but with actual weight loss, and dehydration.  Dogs also commonly develop cataracts whereas cats seldom develop cataracts secondary to diabetes mellitus. 
...polyuria (PU) - frequent and more productive urination
...polydipsia (PD) - increased water intake
...polyphagia - excessive appetite
...weight loss
...lethargy
...sugar in the urine

The buildup of sugar in the blood stream makes the blood more "concentrated" (doctors use the term higher osmolality) and the brain signals a need to drink more water to dilute the blood.  PD (polydipsia) is the result... the animal drinks excessive amounts of water.  Of course the animal then needs to urinate more often and in greater than normal amounts.  This increased urination is called PU (polyuria).  Weight loss occurs even in the presence of an increased appetite because the carbohydrate consumed cannot be used for energy or stored as fat and because the animal metabolizes its own fat and tissue protein for energy instead of utilizing the dietary carbohydrate. If left untreated, diabetes mellitus leads to muscle wasting, depression, vomiting, kidney failure and death.  Some dogs develop ocular cataracts quite rapidly and this is another sign that may lead to getting the animal in for an examination by the veterinarian.  In cats, often the owner will notice a wobbly gait or weakness in walking or jumping.  Muscle wasting and weakness are also commonly seen in diabetic cats.

Insulin injections, daily or twice a day, can be a true life saver for dogs and cats with diabetes mellitus.  There are now special diets made just for diabetic dogs and cats, too.  These are prescription only diets and can play an important role in maintaining the diabetic patient.  It is important to note that for optimum blood glucose levels to be maintained the dog or cat needs to have three parameters in balance on a day-to-day basis:
1.  The amount and timing of exercise should be the same every day.
2.  The amount of food and time of feeding should be the same every day.
3.  The amount of Insulin administered and time of administration should be the same each day.

If any one of these three parameters are different on any given day, the requirements of the other two parameters will be changed.  For example, if a patient gets the usual amount of exercise today as normal but won't eat its usual meal, then the patient may need considerably less Insulin in that day's injection.  If you have already administered the insulin you can't take it back!  If the usual amount of Insulin is given and the pet doesn't eat its routine meal, the pet may become hypoglycemic and develop signs of low blood sugar.  Keeping the diabetic pet regulated in the three areas detailed above will enhance the animal's quality of life.

LOW BLOOD SUGAR... Hypoglycemia
If an animal's blood sugar level becomes so low that the energy needs of the cells are not met, the cells begin to suffer and lose their ability to function.  Especially true with nerve and muscle cells that have high respiratory rates and that need continuous oxygen and glucose for survival, a lack of glucose results in rapid deterioration of function.  The usual signs in a dog that the blood sugar level is too low are trembling, agitation and muscle incoordination.  Ultimately a seizure may occur.  Hypoglycemic cats display salivation, muscle tremors and weakness and sometimes panting (open mouth breathing in a cat is considered to be abnormal).  These animals need a quick source of energy in the form of carbohydrates and may not survive hypoglycemia if oral or intravenous sugars are not administered.  Any diabetic dog or cat should be closely monitored for signs of hypoglycemia, especially if the animal vomits or skips a meal and insulin has been administered.  The insulin will drive much of the circulating glucose into the cells and if there is no recent dietary source of additional glucose, hypoglycemia may result.  As well, if the diabetic animal engages in an unusual session of vigorous physical activity, it may deplete the glucose stores in the body and become hypoglycemic.

TREATMENT FOR DIABETES                     NOTE!  Each case is different and requires careful individual assessment by a veterinarian.  The following presentation is one veterinarian's summary of Insulin Therapy.  It is written by a veterinarian who also happens to be a diabetic.  Your veterinarian's suggestions and recommendations may vary significantly from this discussion.

Generally start canine patients with NPH insulin at ¼ unit per pound of body weight twice/day with twice/day feeding.  Ideally, one can generate an insulin response curve with the NPH, but its general action is over the course of twelve hours.  It’s always best to try to regulate a dog on his own home schedule and activity, so frequent blood glucose checking in the early weeks after diagnosis is important.  Usually client education on diet and exercise, and problems with treating anxiety (both the owner’s and the dog’s), feeding and dosing schedule can be discussed and accommodated in these first few weeks after the diagnosis of diabetes is made.

Dogs that are presented with diabetic ketoacidosis (DKA) is a dangerous situation where the patient has been afflicted with diabetes for some time and the body chemistry is way off balance.  Ketoacidosis results from utilization of body protein sources such as muscle for energy because glucose is unable to be utilized.  These patients are often treated with the fast acting insulins.  This does require more frequent blood glucose checking (hourly or every 2 hours) to avoid hypoglycemia until stable normal glucose levels are reached and maintained, the dog feels better and accompanying medical concerns are addressed.  The most commonly available insulins today are the “human insulins” made with recombinant DNA processes to more closely resemble the human insulin molecules.  Dog insulin is more similar to the pork and beef sources of insulin, which still can be available from pharmacies, but require specific a request to obtain them. 

Follow-up glucose checking on dogs that appear to be doing well is recommended about every two to three months.  Some owners have obtained their own glucose meters to more closely follow their dog's blood sugar levels at home.  Generally, the complications from diabetes that humans are concerned about such as nephropathy (kidney disease), retinopathy (damage to the back lining of the inside the eye), and nerve disease occur over many years. Most dogs to not have a natural life span long enough to expect these sorts of complications.  Cataracts (lens pathology) in dogs subsequent to diabetes is quite common, though, and may need to be surgically removed if vision is impaired.

Experimentation with dogs was essential in the early 20^th century for an understanding of what diabetes was and for the discovery of insulin and its purification from the pancreases of slaughtered meat animals for use in treating diabetes.  Now, people look forward to advances on the medical horizon such as pancreatic islet cell transplantation, potential growth of pancreatic islet cells from stem cell research, or assistance from pigs cloned to have cells missing the rejection markers.  What this will mean for treatment possibilities in dogs is still unknown.

Keep in mind that any animal that is being treated with insulin for Diabetes Mellitus should have a structured lifestyle.  That means the patients should get about the same amount of exercise every day, eat about the same amount of food and at about the same time each day, and then the insulin dose can be regulated consistently every day.  If you change any one of the three variables (exercise, caloric intake, insulin dose) it has an effect on the blood sugar levels.   Normally, a dog's blood sugar varies between 70 and 120 mg/dL.  A cat's normal blood sugar has a wider normal range and can be between 70 and 160 mg/dL.  Learn more about dog and cat normal blood values here.  Consistency in the patient's lifestyle will greatly assist proper dosing of insulin and result in a happier, healthier pet.

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