Dog Diabetes Mellitus
Diabetes mellitus is an endocrine disease involving the pancreas. Normally, beta cells present in the pancreas secrete the hormone insulin, but in diabetes mellitus, insulin secretion from the beta cells is greatly diminished. Insulin is important in many areas of the body, and the clinical signs of diabetes are a result of this lack of insulin.
Development of diabetes mellitus in dogs
How diabetes mellitus develops remains unclear. Genetic predisposition has been suggested in several breeds, especially the keeshond, where beta cells may fail to develop. Animals with less severe abnormalities of the beta cells may be predisposed to the development of diabetes after exposure to toxic chemicals, viral infections, and chronic stress. Immune-mediated destruction of beta cells is a factor in the development of diabetes in humans, and similar mechanisms may occur in dogs. Recurring inflammation of the pancreas (pancreatitis) may also play a role in the development of diabetes in some animals.
Which dogs suffer from diabetes mellitus?
The incidence of diabetes mellitus in dogs is approximately 1 in 200 animals. Peak incidence occurs between the ages of 7 and 9 years, with a range of 4 to 14 years old. Female dogs are affected more often than males. Breeds that appear to be at a higher risk of diabetes mellitus are keeshonden, pulik, Cairn terriers, miniature pinschers, poodles, dachshunds, miniature schnauzers, and beagles. A number of breeds, including cocker spaniels, German shepherds, collies, Pekingese, rottweilers, and boxers, appear to be at a lower risk for developing diabetes mellitus.
What does diabetes mellitus in dogs actually mean?
The deficiency of insulin in diabetes affects many different body systems. Insulin is necessary for the uptake of glucose by cells in the body, and a deficiency results in an increase in glucose in the blood stream (hyperglycemia). Normally, any glucose that is filtered by the kidney is reabsorbed, but as the blood glucose concentration rises, the kidney cells cannot reabsorb the extra glucose, and glucose spills over into the urine. This happens when serum glucose exceeds approximately 180 mg/dL. The increased glucose in the urine causes an increased amount of water to be excreted in the urine, and thus there is an increase in urine volume. With the loss of extra water in urine, the animal must drink extra water to prevent becoming dehydrated.
Insulin is necessary for glucose to enter cells, but in diabetes, the lack of insulin prohibits the entry of glucose. Since glucose cannot enter cells to provide their energy, the body senses that it is in a state of starvation. This leads to a chain reaction of events, that contribute to the worsening of the disease. Protein catabolism increases, releasing amino acids. Fat breakdown occurs, releasing fatty acids that are used for ketone body production. The glycerol that results from fat breakdown is used to produce more glucose by the body. And since this glucose can't get into the cells due to the insulin deficiency, the blood glucose level climbs even higher. This hyperglycemia causes dehydration due to the loss of water in urine. Decreased blood volume (hypovolemia) results, which stimulates further mechanisms that promote glucose production. Thus this vicious cycle of increased glucose production, decreased glucose utilization, and protein and fat breakdown continues. In addition, the amount of glucose entering the cells in the satiety center in the hypothalamus controls the feeling of hunger. Little glucose is able to enter these cells due to the insulin deficiency, and thus the animal feels hungry continually. The increased food intake further contributes to the hyperglycemia, and body tissue breakdown. This accounts for the loss of weight that is seen in uncontrolled diabetics, even though their appetite is increased. The dehydration and hypovolemia that results can lead to acid/base imbalances and diabetic ketoacidosis, in which the dog is severely ill.
As a result of the deficiency of insulin, clinical signs are typically loss of weight, increased thirst, increased urination, and increased hunger. Occasionally, cataract formation may be the first sign of diabetes that is noticed. Dogs may have been affected by diabetes for 6 months before the owner warrants the signs severe enough to visit their veterinarian.
Treatment of diabetes mellitus in dogs
By the time diabetes mellitus is diagnosed, almost all dogs require life-long insulin therapy. There are many types of insulin available, and this choice is based on each individual case. Most dogs receive one daily insulin injection initially, but many require two injections per day to achieve good control of the blood glucose concentration. The goal of treatment is to eliminate the clinical signs of diabetes. Once the diabetes is controlled, reevaluation is recommended every two to four months. If clinical signs reappear suddenly, the patient must be reevaluated immediately.
Diet and feeding schedule are very important in the diabetic dog. Typically, if the dog receives one injection of insulin per day, one-half of the day's food is fed at the time of insulin injection, and the other half is fed approximately 8 to 10 hours later. If the dog is getting two insulin injections per day, then one-half of the day's food is fed at each injection time. Feeding and injection schedules must be followed closely, occurring at the same time each day. The diet being fed should be nutritionally balanced and complete, with consistent proportions of carbohydrate, fat and protein. Homemade diets are not recommended, since this consistency is difficult to maintain. A typical diet should supply more than 40% of the calories from carbohydrate, and less than 25% of the calories from fat. Fiber content should be moderate in amount, and the protein source should be of high quality and highly digestible. Proteins from eggs and meats (chicken, lamb, etc.) are preferable to proteins from cereal sources (soybean meal, corn gluten meal). If the dog is overweight, it should be put on a gradual reducing diet . In some animals, obesity may contribute to insulin resistance, and as their weight decreases, their diabetes will improve.
Complications with diabetes mellitus in dogs
Complications of chronic diabetes mellitus include cataract formation, retinopathy, neuropathy, and nephropathy. The formation of cataracts is the most common long term complication, resulting from the elevated levels of serum glucose. Elevated glucose levels in the lens metabolize to other sugars, which draw water into the lens. This causes swelling of the lens fibers and the formation of cataracts. Development of cataracts can occur quickly, and the dog may become blind in a matter of days. Good control of the diabetes and blood glucose level will help decrease the incidence of cataracts. Retinopathy is the result of small hemorrhages in the retina, and can lead to blindness. Diabetic retinopathy is an uncommon occurrence in animals. Neuropathy, including weakness, muscle atrophy, and decreased reflexes, is also rare in dogs. Nephropathy, in which kidney function declines, is also uncommon in animals.
Maintaining the diabetic animal requires strict adherence to feeding and insulin injection schedules, and is a commitment for the life of the dog. With good control of serum glucose levels, many diabetic dogs can lead happy, active lives, with relatively few complications.