Diabetes mellitus (or "sugar diabetes") is a relatively common disease seen in dogs and cats. Insulin — normally produced by the pancreas — is the hormone required for the body's tissues to take in and utilize glucose (sugar). Diabetes mellitus results when insulin is no longer produced by the pancreas or when the body's tissues do not respond to the insulin that is present.
Without insulin, glucose starts to accumulate in the blood because the body's tissues cannot take any glucose in. Because glucose is the major energy source for the body, the body's tissues essentially begin to starve. In addition, as the blood sugar becomes higher and higher, the sugar starts to spill over into the urine along with water; therefore, diabetics urinate large volumes. Pets may start to have urinary accidents indoors. Because the volume of fluid lost through the urine is increased, pets begin to drink more to compensate. Because the body's tissues are starving, most diabetics also eat more but usually lose weight. The hallmark symptoms of diabetes mellitus are excessive thirst, excessive urination, increased appetite, and weight loss. Be especially suspicious of diabetes mellitus if you notice the floor to be sticky where your pet has a urinary accident.
Two forms of diabetes exist. Type I (or insulin-dependent) diabetes is the form where the patient is not producing any insulin. Virtually 100% of diabetic dogs have this form. Type II (or non-insulin-dependent) diabetes is the form where the patient has insulin but either does not have enough or has a condition that interferes with insulin function. As many as 50% of cats may have this form. Obesity is thought to be the primary cause of Type II diabetes in cats. Weight reduction and a shift away from high carbohydrate foods may lessen the amount of insulin required or allow a cat to go off insulin altogether.
Besides the symptoms listed above, the problems caused by diabetes mellitus can be much more extensive. Diabetics tend to be more prone to infection due to impairment of the immune system. Eye problems (especially of the lens and retina) are common and can result in blindness. Dogs are especially prone to cataract formation even if well-regulated with insulin. If untreated, the excessive levels of glucose in the blood eventually result in a disease state called ketoacidosis — a potentially lethal buildup of toxins in the bloodstream. Ketoacidotic animals act lethargic, vomit, may not eat, and can become profoundly dehydrated. Not only are these animals diabetic, but they are sick from their diabetes. Diabetes mellitus must always be viewed as a very serious disease.
Diagnosis is relatively straightforward by a simple blood test. Finding elevated levels of glucose in the blood after a 10-12 hour fast is considered diagnostic. Cats can present more of a challenge due a phenomenon called "stress hyperglycemia." Scared or nervous cats (practically any cat that has endured a car ride to the veterinary hospital!) can have a blood sugar as high as 300-350 mg/dL (normal: about 120-150 mg/dL). This does not represent true diabetes mellitus, but rather a normal response to fright. These cats may require several repeat tests to identify trends in their blood sugar levels. More sophisticated blood tests are also available that are not influenced by fright.
Virtually all dogs and many cats require insulin injections to manage their diabetes. Giving injections to a pet can be intimidating to many owners, but becomes quite easy with experience. We will train you how to properly handle insulin and how to give your pet injections. The process of finding the optimal dose of insulin that your pet requires can be time-consuming, frustrating, and sometimes expensive. This process — called insulin regulation — involves regular checks of your pet's blood glucose. It is necessary to have the glucose checked at different times of day since all animals respond differently to insulin. Adjustments in your pet's insulin dose must be made under the careful supervision of a veterinarian. If your pet is not receiving enough insulin, the symptoms of diabetes will persist. If your pet receives too much insulin, the blood sugar level can drop too low, resulting in weakness, mental dullness, lethargy, and sometimes seizures or coma.
It is important to understand early on that lifestyle changes are necessary to properly manage your pet's diabetes. For some owners, these changes can be a significant burden. For example, your pet's food intake must be standardized; this includes the type of food, quantity of food, and time of day food is eaten. Activity level should be similar from day to day. Insulin needs to be administered at nearly the same time each day; for pets on twice-daily insulin, the injections should be approximately 12 hours apart. Insulin regulation will become difficult or impossible if too many variables in lifestyle are not controlled.
In addition to blood glucose testing, the doctor will also rely heavily on your observations regarding how your pet is doing at home. For example, parameters such as thirst, urination, appetite, and activity level should all be carefully monitored by you. This will help the doctor fine-tune your pet's insulin dose. Fewer complications are likely to arise if your pet is well-regulated on insulin.
Diet seems to play an even more critical role in cats. Many of the traditional dry cat foods are too high in carbohydrates. Since natural feline physiology relies on a high-protein, meat-based diet, we are now recommending high protein canned diets for most feline diabetics. In some instances, we have been able to get cats off insulin by switching to a high-protein canned diet. Another exciting breakthrough with feline diabetes mellitus is the use of glargine (Lantus®) and protamine zinc (ProZinc™) insulins. These are relatively new insulins that seem to control feline blood sugar extremely well. Amazingly, blood sugar is often so well-controlled that some cats may be able to come off insulin altogether.
Although the lifestyle changes and ongoing treatments can be frustrating to owners after diagnosis, many diabetic pets lead full, happy lives. This disease must be treated properly and have a committed owner to maximize the likelihood of success.