Diabetes mellitus is one of the most common endocrine diseases seen in general practice. It is fundamentally a defect of the carbohydrate metabolism in affected patients, which leads to a deficiency in insulin. Diabetes can be classified as either Type 1 (lack of insulin production) or Type II (impaired insulin production along with an inadequate response to the hormone). The most common form of the disease in dogs is Type 1, insulin-dependent diabetes, which occurs when the insulin produced by the pancreas is inadequate. Dogs who have Type I require insulin therapy to survive. This is due to the beta-cells of the pancreas, which should produce insulin, losing their function irreversibly. Type II diabetes is found in cats and is due to a lack of normal response to insulin.
The underlying cause is poorly understood, but there are a variety of factors involved, including genetic predisposition, infection, inflammatory damage to the pancreas (pancreatitis), progressive immune-mediated destruction of pancreatic cells, obesity or long-term use of corticosteroids as well as other insulin-antagonistic diseases. It tends to be a disease seen in older patients, with over 70% of dogs being older than 7 years at the time of first diagnosis. Females tend to be affected more than male dogs.
So, what happens in diabetic dogs? The end result is high blood glucose levels, which is known as hyperglycaemia. The disturbance in carbohydrate metabolism results in the liver producing more glucose, and the body not being able to use it effectively due to the lack of insulin. Once the glucose level exceeds the renal threshold (which is 180 to 220mg/dl in dogs), not only will glucose be present in the urine, but there is an osmotic diuresis, which leads to increased thirst (polydipsia). With time, the dog develops a catabolic state, where there is a resultant weight loss despite normal or excessive food consumption. The other complication if diabetes is left untreated is that the tissues become starved of energy and so the liver produces ketoacids at a higher rate, which can lead to ketoacidosis. Ketoacidosis is a life-threatening state and must be treated aggressively.
Animals with diabetes classically present with polyuria (increased urination), and polydipsia (increased thirst) as well as weight loss. Owners also often report an increased appetite. Occasionally an owner may present an animal for sudden blindness caused by cataract formation. The veterinary surgeon will then find persistent hyperglycaemia in blood tests or glucosuria (glucose in the urine). Ketones can be detected in the urine of 66% of dogs with diabetes at initial presentation.
It is also important to rule out other underlying diseases such as Cushing’s disease or pancreatitis, which may also lead to a carbohydrate intolerance. Further blood tests and ultrasound may be used to rule out these conditions. Intact bitches have higher and fluctuating progesterone levels, which can also cause imbalances to carbohydrate metabolism. All intact diabetic dogs should be spayed to make insulin management more consistent. It is not uncommon for diabetic dogs to have urinary tract infections, as the glucose in the urine provides nutrition for bacterial growth. These should also be treated appropriately.
The main goal of therapy is to eliminate the clinical signs and prevent the long-term complications of diabetes (cataract and ketoacidosis). Most dogs can be well managed by injecting insulin under the skin twice daily. An intermediate-duration-of-action insulin is used. It is recommended that patients are fed two equal meals at the time of insulin administration. This will prevent fluctuations in the glucose curve (glucose levels throughout the day). It can take several days for the dog to adjust to the insulin dose, and so glucose curve monitoring is more accurate 5-7 days after dosage changes of insulin. Since each dog may react differently to the insulin product, it is important to ensure thorough monitoring of glucose levels, especially at the beginning of therapy, until the adequate insulin dose is found. It usually takes 4-6 weeks for the optimal protocol to be achieved. Hand-held glucose meters are relatively easy to use and many owners measure their dogs blood glucose levels at home. The optimal dose of insulin will keep the glucose between 80 and 150mg/dl. In addition, it is important to ensure the glucose level does not fall too low, i.e. under 65mg/dl, which would be called hypoglycaemia. Hypoglycaemia is the most serious complication of diabetes and can even be fatal. If signs such as weakness, seizures or trembling occur, owners must apply a syrup or honey to the gingiva of the oral cavity and seek veterinary advice. Insulin must not be given. It should also be noted that any other underlying diseases that may impact the effectiveness of insulin must also be addressed.
Monitoring glycemic control is a vital part of diabetic management. However, the most important parameter is the assessment of clinical signs and overall health of the animal. In combination with glucose curves, urinalysis and fructosamine level monitoring your vet will be able to assess the success of management. Fructosamine is a measure of the average blood glucose over the previous 2 to 3 weeks. The fructosamine level is not affected by short term excitement or stress like glucose is.
Special diets that are high in fiber, low in simple sugars, and moderately restricted in fat and protein are recommended. Your veterinary surgeon will advise you on a prescription diet best suited to your animal. It is of vital importance that diabetic animals eat regularly and consistently, i.e. two meals a day at the same time of day and not given poor quality treats high in fat and sugar.
Exercise effects both the absorption of insulin and the metabolic use of glucose and is an important element in maintaining glycemic control. It is important that diabetic animals receive a constant level of activity at roughly the same times of the day. Strenuous and sporadic exercise can lead to low blood sugar, and so regular exercise should be part of a daily routine.
In conclusion, most diabetic animals live a happy and fulfilled life if the diabetes is well managed. Complications like cataract formation can be avoided if the blood glucose levels remain under 180mg/dl. The prognosis depends on the presence and reversibility of any concurrent diseases and ease of management of the patient.