Affects: Cats, Dogs
Diabetes mellitus is a disease in which the beta cells of the endocrine pancreas either stop producing insulin or can no longer produce it in enough quantity for the body's needs. It is the most common disorder of the endocrine pancreas.
The condition is treatable and need not shorten the animal's life span or interfere with the quality of life. If left untreated, the condition can lead to cataracts, increasing weakness in the legs (neuropathy), malnutrition, ketoacidosis, dehydration, and death. Diabetes mainly affects middle-aged and older dogs, but there are juvenile cases. The typical canine diabetes patient is middle-aged, female, and overweight at diagnosis.
The number of dogs diagnosed with diabetes mellitus has increased three-fold in thirty years. In survival rates from around the same time, only 50% survived the first 60 days after diagnosis and went on to be successfully treated at home. Currently, diabetic dogs receiving treatment have the same expected lifespan as non-diabetic dogs of the same age and gender.
Symptoms: The main symptoms which occur in nearly all dogs with diabetes mellitus are:
excessive water consumption; this condition is often called polydipsia.
frequent and/or excessive urination, known as polyuria, often requiring the dog to be let outside to urinate during the night,
abnormal increase in appetite, a condition known as polyphagia.,
weight loss; dogs with diabetes may also suffer from severe weight loss, weakness, anorexia and blindness.
Pathogenesis: The body uses glucose for energy. Without insulin, glucose is unable to enter the cells where it will be used for this and other anabolic ("building up") purposes, such as the synthesis of glycogen, proteins, and fatty acids. Insulin is also an active preventor of the breakdown or catabolism of glycogen and fat. The absence of sufficient insulin causes this breaking-down process to be accelerated; it is the mechanism behind metabolizing fat instead of glucose and the appearance of ketones.
Since the glucose that normally enters the cells is unable to do so without insulin, it begins to build up in the blood where it can be seen as hyperglycemia or high blood glucose levels. The tubules of the kidneys are normally able to re-absorb glucose, but they are unable to handle and process the amount of glucose they are being presented with. At this point, which is called the renal threshold, the excess glucose spills into the urine (glycosuria), where it can be seen in urine glucose testing. It is the polyuria, or over-frequent urination, which causes polydipsia, or excessive water consumption, through an osmotic process. Even though there is an overabundance of glucose, the lack of insulin does not allow it to enter the cells. As a result, they are not able to receive nourishment from their normal glucose source. The body begins using fat for this purpose, causing weight loss; the process is similar to that of starvation.
Management: Early diagnosis and treatment can reduce the incidence of complications such as cataracts and neuropathy. Since dogs are insulin dependent, oral diabetes drugs, which require a functional endocrine pancreas with beta cells capable of producing insulin, are ineffective. Diabetic dogs require insulin therapy, which must be continued for life.
The goal of treatment is to regulate blood glucose using insulin and some probable diet and daily routine changes. The process may take a few weeks or many months and is similar as in type 1 diabetic humans. The aim is to keep the blood glucose values in an acceptable range. The commonly recommended dosing method is by "starting low and going slow" as indicated for people with diabetes.
During the initial process of regulation and periodically thereafter, the effectiveness of the insulin dose at controlling blood glucose is evaluated. This is done by a series of blood glucose tests called a curve. Blood samples are taken and tested at intervals of one to two hours over a 12- or 24-hour period. The results are generally transferred into graph form for easier interpretation. They are compared against the feeding and insulin injection times for judgment. The curve provides information regarding the action of the insulin in the animal. It is used to determine insulin dose adjustments, determine lowest and highest blood glucose levels, discover insulin duration and, in the case of continued hyperglycemia, whether the cause is insufficient insulin dose or Somogyi rebound, where blood glucose levels initially reach hypoglycemic levels and are brought to hyperglycemic ones by the body's counterregulatory hormones. Curves also provide evidence of insulin resistance which may be caused by medications other than insulin or by disorders other than diabetes which further testing can help identify.
Other diagnostic tests to determine the level of diabetic control are fructosamine and glycated hemoglobin (GHb) blood tests which can be useful especially if stress may be a factor. While anxiety or stress may influence the results of blood or urine glucose tests, both of these tests measure glycated proteins, which are not affected by them. Fructosamine testing provides information about blood glucose control for an approximate 2- to 4-week period, while GHb tests measure a 2- to 4-month period. Each of these tests has its own limitations and drawbacks and neither are intended to be replacements for blood glucose testing and curves, but are to be used to supplement the information gained from them. While HbA1c tests are a common diagnostic for diabetes in humans, only recently has an A1C test become available for cats and dogs. The product is called A1CARE and is available from Baycom Diagnostics.