Diabetes Mellitus in Cats
Diabetes is a metabolic disorder that results from functional or absolute insulin deficiency. Insulin is the chief regulator of the path that dietary sugar takes, but also affects fat and protein metabolism, and malfunction of this metabolism has an impact on all body systems.
In humans, we speak of Type I, or insulin dependent diabetes, which is often a juvenile onset condition, and requires insulin administration for effective treatment. Type II is often seen in middle aged, inactive patients and this type often is treated without insulin administration.
In cats, these types also exist, but making a distinction between these two types is not as easy to do, at least initially. Newer information confirms that this way of looking at cats is not really accurate. Cats are insulin responsive diabetics.
There is no single cause of this condition, but some diseases (Cushing's disease for example), pancreatic inflammation, and certain drugs (steroids) are known to be associated with development of diabetes. Obese body condition is a risk factor in adult cats, and immune-mediated disorders can trigger destruction of the beta cells in the pancreas that produce insulin. In cats, amyloid deposits are frequently seen on tissue samples. These deposits interfere with pancreas function and lead to progression from type II to type I diabetes as more cells die off.
In diabetics, tissues cannot uptake and utilize all of the important food components (sugar, fat, protein) and this effectively puts the body into starvation mode. In the very early stages, reduced activity and reduced appetite and grooming may be the first signs. Severe diabetes results in weight loss, increased thirst and urination, nerve problems (cats often walk down on their hock joints of the back legs - plantigrade diabetic neuropathy), liver failure +/- jaundice, and increased risk of all chronic infections. In very late stages, complete loss of appetite, vomiting, weakness, and death may occur. There are some severe but rare complications of uncontrolled diabetes such as non-ketotic hyperosmolar diabetes, and ketoacidotic crises may arise as well.
Note that the eye cataracts that we see in dog and human diabetics are not reported in cats.
No particular breeds of cats are known to be at risk for diabetes though some lines of Burmese cats have been shown to have increased risk. Diabetes can strike cats aged anywhere between 1 year and 19 years of age.
Diagnosis is made by performing a complete blood count, biochemical profile, urinalysis, and noting appropriate history signs (changes in thirst, body weight, urinations etc.). The veterinarian may use a machine (e.g., Glucometer®) to measure blood sugars over a period of time to make sure that blood sugar elevations are caused by diabetes and not due to a peak from stress. Cats can develop quite a high blood sugar while stressed (you guessed it- white coats and veterinary hospitals!), but if the sugar is up due to stress, it will not stay elevated. Stress induced sugar elevation will also not produce changes at home such as thirst, appetite, and weight changes.
The urine sugar level is also elevated in diabetes, but is not used alone to diagnose this condition. More importantly, the urine sample helps us to quickly check for ketones, a metabolic by-product that can indicate complications of diabetes that require intensive intervention. Blood insulin levels are also available. Glucose tolerance tests are widely used in humans for diagnosis, but because of quirks of the feline species, it is not used as a screening test in cats. Fructosamine blood tests can measure longer term blood sugar trends and are an excellent way to distinguish true diabetes from stress hyperglycemia. These must be sent out to a laboratory for analysis.
Treatment must be provided. The veterinarian may need to try more than one strategy with a cat. Diabetic cats are more difficult to control than dogs or humans. The good news is that cats tolerate borderline high normal sugar levels with less chance of complications than dogs or humans, and so do not need to be quite so rigidly controlled. This is great because cats are not particularly impressed with our therapies (as would be expected for a cat) and many do not like to eat all of their food at once, so blood sugar swings are less predictable over the day and night.
Recently, a home blood glucose monitoring initiative was reported in the literature that provided a practical method for owners to check blood sugar at home by doing a small prick in the ear using a low volume automated glucose meter. This is a big step forward in feline diabetes management because it is well known that while in hospital for monitoring, cats tend to not eat well and are stressed, both of which can interfere with blood sugar assessment. It is important to have a blood glucose curve done after insulin therapy is begun so that the veterinarian can check how quickly a particular cat processes the insulin type prescribed. Cats have a very wide spectrum of time that it takes to metabolize the insulin, and this test is very important for the safety of long-term insulin therapy. The curve is usually done over the course of a full day stay at the hospital about 3-6 days after insulin treatment begins. If type of insulin is changed, the curve needs to be repeated. Though it is not an accurate check of absolute blood glucose levels due the stress, the trend will confirm how the cat metabolizes insulin.
For longer term management, the use of the laboratory tests (serum fructosamine) tests can help track long-term typical blood sugar levels. This is particularly helpful for fractious cats that get very stressed when handled for blood sampling.
Other helpful suggestions for management include regular exercise (play sessions with the cat are fun!), and dietary adjustment. The diet must be customized to each patient. What is right for a middle aged obese diabetic cat is wrong for a severely underweight diabetic. Though traditionally, twice daily feeding has been prescribed, most feline veterinarians suggest cats "nibble" at a set volume of food left out with free access over 24 hours.
New advances in feline nutrition have led to a new approach to dietary management of diabetic cats. In the past, fibre in the diet was used to help slow sugar absorption into the bloodstream from the gut. Now we know that provision of a diet with high protein, low carbohydrate and lower fibre will provide optimal nutrition. These new diets have been shown to help reduce the amount of insulin given, or even eliminate the need for it. They provide healthy weight loss since the intake nutrient balance most closely approximates a cats feral diet.
You may have heard of hypoglycemic drugs. If a fairly healthy diabetic is in the early stages, the oral medications may be suggested as an alternative to insulin injections along with a dietary change. A large number of cats ½(over 50%) do not respond to this approach, or may take a long time (1-2 months) to respond, but it does provide an option for preliminary management. Inevitably, the cat will need insulin at some point. Recent research findings indicate going straight to insulin therapy has advantages, so the oral hypoglycemic medications are much less commonly prescribed today.
All cats will progress to insulin dependent diabetes as amyloid deposits continue to build in the pancreas. Some cats with mild diabetes will revert to normal after insulin injections have begun, so careful attention to control is needed in cats to avoid low blood sugar crisis (hypoglycemia).
Treating diabetes takes commitment from the owner. It is essential to cooperate for follow up evaluations, and carry out ongoing adjustments for the treatment program to ensure the proper application of care. With good care though, the diabetic cat can have a decent quality of life. With gentle administration of the insulin using tiny needles, most cats tolerate treatment very well, and some kitties even run over to receive their insulin injections if a little treat reward is offered for cooperation!