DVM Iida Niinikoski
Diabetes mellitus is a fairly common disease in the modern day domestic cat. Out of 200 cats, approximately 1-2 develop diabetes during their lifetime. In diabetes mellitus the blood glucose level of the cat is constantly too high. Feline diabetes is similar to type II diabetes mellitus in humans. The corner stones of treatment of diabetes are effective insulin treatment early on in the disease, diet and avoidance of obesity. With aggressive treatment early on combined with efficient monitoring, some cats go into remission and can be managed without insulin later on.
Insulin is a hormone secreted by the beta cells of the pancreas. It increases the movement of glucose in the blood into cells of the body, which in turn decreases the amount of glucose in the blood. Insulin resistance occurs often early on in the disease: insulin is secreted by the pancreas, but it does not function properly in the body. This means that blood glucose levels remain high. Obesity, certain diseases (e.g. acromegaly and inflammatory conditions) as well as some medications (e.g. cortisone) are known to cause insulin resistance.
Due to insulin resistance blood glucose level is high, which leads the pancreatic beta cells to secrete even more insulin. If insulin resistance continues, the beta cells tire, and the production of insulin decreases or completely stops. Insulin production might normalize early on in the disease process if the factors causing insulin resistance are gotten under control. Lifelong treatment with insulin is needed if the destruction of pancreatic beta cells is complete. The avoidance of obesity is key to preventing diabetes. A diet high in protein and low in carbohydrates improves glucose balance and reduces insulin resistance.
Multiple risk factors besides obesity have been identified. These include increasing age, male gender and physical inactivity. Some breeds such as the Burmese cat are more at risk for development of diabetes. The typical diabetic patient is an overweight 11-13-year-old male cat who lives indoors.
Typical signs of diabetes are excessive drinking and urinating. The cat loses weight despite having a good appetite. The signs progress slowly, and it is often difficult to say exactly when they started. If left untreated, the disease leads to diabetic ketoacidosis, in which vomiting and extreme fatigue occur. Diabetic ketoacidosis is a life-threatening condition.
If diabetes is suspected a blood and urine sample are taken at the vet. The diagnosis is based on clinical signs combined with the laboratory results. Blood glucose in cats is affected by stress (caused by a visit to the vet for example), so just a slightly high blood glucose value does not necessarily mean the cat is diabetic. A high fructosamine value supports the diagnosis of diabetes, as it describes blood glucose levels from the past few weeks.
The goal of treatment is to keep blood glucose at a level where the signs of diabetes are nonexistent and the quality of life of the cat is good. Drinking and urinating are not excessive, and the cat is bright and alert. Too high and too low blood glucose levels are avoided. The primary goal in recently diagnosed diabetic cats should be remission, in which insulin is no longer needed after the initial treatment period. This often requires tight monitoring of blood glucose levels.
The management of diabetes requires a lot of commitment from the owner. Diabetes is treated by subcutaneous injections of insulin. Usually the cats tolerate the injections well, but repetitive injections combined with tight monitoring might cause stress. The type and dosage of insulin is determined by the treating veterinarian. Oral diabetes medications are often ineffective and are not considered a first-line treatment.
Home monitoring of blood glucose levels is an important part of the treatment, especially if aiming for remission. Portable blood glucose meters are easy to use. Blood glucose curves can be done to see how low the blood glucose level drops after injection of insulin and how long the effect of the injection lasts. In some cases urine dipstick tests can be used for detection of glucose in the urine, but this is not a reliable method of monitoring blood glucose levels on its own.
A diet with high protein and low carbohydrate helps keep blood glucose levels stable. Commercial diets for diabetic cats are available. Feeding of canned food instead of dry food is recommended because of the lower caloric density and ease of portion control.
The weight of the cat is monitored at home: obesity is avoided but fast weight loss might be indicative of poor control of the disease. Intentional weight loss needs to be slow and gradual. Moderate exercise is beneficial and improves weight control and general well-being. Playing and climbing should be encouraged. Changes in appetite, drinking and urinating need to be noted. When blood glucose levels are too high, the excess glucose is excreted in urine. Glucose pulls out a lot of water with it, which increases the amount of urine and thus the amount of water the cat needs to drink.
Visits to the veterinarian are frequent especially in the beginning of management of the diabetic cat. Blood glucose and fructosamine levels are monitored. Diabetes predisposes the cat to developing urinary tract infections and urine samples are controlled. Blood tests are checked for signs of other issues, because blood glucose balance is strongly affected by different inflammatory conditions as well as other diseases. Dental care is very important. If the disease is gotten well under control the frequency of veterinary visits can be decreased.
Hypoglycemia, low blood glucose, may occur rapidly and be life-threatening. Hypoglycemia may be due to an overdose of insulin due to insulin administration issues or if the pancreas has started secreting insulin and the cat is going into remission. Administration of insulin if the cat is not eating or is vomiting may also lead to hypoglycemia. Chronic hypoglycemia occurs when insulin is administered subcutaneously even though the pancreas has recovered and the production of insulin has begun. Hypoglycemia does not provoke hunger in cats, so the situation is not corrected by the cat eating on its own. The importance of blood glucose monitoring cannot be stressed enough.
Signs of hypoglycemia in cats may be very vague and variable and range from lethargy, ataxia and tremors to coma. Rapid treatment is required. If the clinical signs are mild, feeding a meal or sugar water/honey is suggested. In more severe cases, honey can be applied to mucous membranes of the cat before transportation to the veterinarian. Severe hypoglycemia requires treatment in-hospital with parenteral glucose.
Complications from hyperglycemia, high blood glucose, develop slower than those associated with hypoglycemia. Hyperglycemia occurs when there is a problem with the injection of insulin, the insulin does not function properly, the insulin dosage is not sufficient or something interferes with insulin function in the body. Diabetic ketoacidosis develops when blood glucose levels have been high for some time and the body starts to use free fatty acids for energy. This results in ketones accumulating in the body. Signs of diabetic ketoacidosis include vomiting, anorexia, excessive drinking and urinating, fatigue and sweet-smelling breath. The condition requires aggressive treatment in-hospital.
Neurological deficits may also be seen with chronic hyperglycemia. The most typical is plantigrade stance, in which the cat walks on the sole of the hindfeet and its heels touch the ground. Muscle atrophy in the hind limbs and difficulty jumping/climbing may be seen before plantigrade stance occurs.
The prognosis of diabetes is better if treatment is started early on. Cats are masters of hiding their illness, and routine veterinary visits and blood samples help with early detection of diabetes and other diseases. Prevention of obesity is essential in the prevention of diabetes and musculoskeletal diseases among others.
Diabetes is a severe disease and its treatment requires a lot of commitment from the owner. With proper management, diabetic cats can live many years of high quality cat life.