Diabetes Mellitus

25 Diabetes Mellitus



David L. Panciera




1. What is the cause of diabetes mellitus in the dog?

The cause in individual dogs is usually unknown and of little importance from a management standpoint, but it is important to note that most dogs with diabetes mellitus have an absolute deficiency of insulin caused by destruction of β-islet cells. Destruction of the islet cells is due to an autoimmune process in some dogs whereas other dogs presumably suffer islet cell destruction secondary to recurrent or chronic pancreatitis. Because either process leads to absolute deficiency of insulin, insulin administration is essential for management of diabetes mellitus in nearly all dogs. However, in some dogs diabetes mellitus results from insulin resistance secondary to hyperadrenocorticism or acromegaly, and treatment of the primary disorder may resolve the diabetes mellitus in these cases.


2. What clinical findings would be expected in a dog with diabetes mellitus?

Polyuria, polydipsia, polyphagia, and weight loss are the most common complaints in dogs found to have diabetes mellitus. Cataracts and blindness are sometimes the first problems noted by the dog’s owner. Anorexia, vomiting, depression, and weakness are usually apparent in dogs with diabetes mellitus complicated by ketoacidosis. Common findings on the physical examination in such dogs include cataracts, hepatomegaly, and obesity. Rarely, peripheral neuropathy may result in weakness and hyporeflexia.


3. How is a diagnosis of diabetes mellitus confirmed?

Persistent fasting hyperglycemia and glycosuria in a dog with clinical signs of diabetes mellitus is adequate confirmation of the diagnosis. A blood glucose concentration above 250 to 300 mg/dl is diagnostic if clinical signs of diabetes are present.


4. What laboratory tests are appropriate, and what are the expected findings in a dog with newly diagnosed diabetes mellitus?

A complete blood count, serum biochemistries, urinalysis, and urine culture are recommended for initial evaluation of all dogs with newly diagnosed diabetes mellitus, in order to identify any concurrent illness or complications. The complete blood count is typically normal in dogs with uncomplicated diabetes. Serum biochemistries typically show, in addition to hyperglycemia, mild to moderate elevations of liver enzymes, hypercholesterolemia, and hypertriglyceridemia. Glycosuria is always found in dogs with diabetes mellitus, and ketonuria is present in more than 50% of diabetic dogs that do not have overt ketoacidosis. Urinary tract infections are common in dogs with diabetes, and because the urine sediment does not contain inflammatory cells in some cases, culturing urine for bacteria is recommended for all diabetic dogs.


5. How should a dog with ketones in its urine but without other clinical evidence of diabetic ketoacidosis be treated?

Ketonuria is a common finding at the time of diagnosis of diabetes mellitus. Unless there are clinical signs of diabetic ketoacidosis, no special treatment is indicated.


6. What are the goals for treatment of diabetes mellitus in dogs?

The goals are to reduce or eliminate clinical signs, prevent complications of diabetes mellitus, maintain euglycemia, and avoid hypoglycemia.


7. What role does diet play in the management of diabetes mellitus in dogs?

A high-fiber diet can be helpful in treating canine diabetes because it can minimize postprandial increases in blood glucose and reduce insulin requirements in some cases. Diets high in simple carbohydrates, specifically semimoist foods, should be avoided. Feeding should coincide with insulin administration and/or peak insulin activity. If insulin is administered twice daily, the dog should be fed 50% of its daily caloric intake at the time of each injection. If insulin is administered once daily, 50% of the food should be fed at the time of injection and the balance 8 to 10 hours later.


8. How does exercise affect management of diabetes in dogs?

Exercise increases insulin delivery to and glucose utilization by the skeletal muscles, resulting in lowering of the blood glucose level. The blood glucose concentration can decrease rapidly and dramatically with exercise that is strenuous and prolonged, such as occurs with hunting. When strenuous exercise is planned, a reduction in the preexercise insulin dose to between 25% and 50% of normal is recommended, and a source of glucose should be available in case hypoglycemia occurs.


9. Are oral hypoglycemic medications effective in dogs with diabetes mellitus?

Oral hypoglycemic medications are not effective in diabetic dogs because most have negligible insulin secretion, so drugs that increase endogenous insulin secretion or cellular insulin sensitivity have inadequate treatment effects.


10. What is the recommended protocol for initiating treatment for diabetes mellitus?

The intermediate-acting insulins, lente insulins, and neutral protamine Hagedorn (NPH) insulins, are recommended for initial management of diabetes mellitus in dogs. The duration of action of lente insulin is slightly longer that of NPH insulin in some dogs. Although the structure of porcine insulin is identical to that of canine insulin, recombinant human insulin can be used successfully as well. Insulin analogues, such as glargine insulin, can be used in dogs, but advantages over other insulins have not been reported. The author currently recommends porcine lente insulin or human recombinant NPH insulin for initial treatment. Twice-daily administration of insulin provides better control than once-daily administration in most dogs, although once-daily insulin administration is effective in some dogs. Because insulin requirements vary considerably between individuals, a conservative initial dose of 0.5 U/kg is recommended. It is recommended that two to three blood samples be obtained 4 to 8 hours after the initial injection to evaluate for hypoglycemia. If hypoglycemia is not present, the dog is discharged to the owner after it has been ascertained that the owner has been thoroughly educated about the disease process, possible complications (cataracts, hypoglycemia), how to monitor the clinical response to insulin, and how to handle and administer insulin. An appointment to assess response to treatment is scheduled for approximately 1 week after discharge.


11. What dose of insulin should be given if the dog does not eat at a normal feeding time?

Because there are many reasons why a dog might not eat at a designated time, the insulin dosage should not be adjusted routinely based on failure to consume all of a single meal. However, if the owner notices signs that the dog is ill or food consumption is decreased for a subsequent meal, the dose of insulin should be reduced by 50%. The dose of insulin should not be skipped altogether unless hypoglycemia is suspected, because ketoacidosis may occur with the combination of lack of insulin, fasting, and possible concurrent illness.


12. How is the response to insulin treatment monitored?

A combination of clinical signs, physical examination findings, and blood glucose determinations is used to assess the response to treatment of diabetes in dogs. An observant owner is often able to assess the response to treatment by monitoring the dog’s activity level, water consumption, urination, and strength. Assessments based on these observations have been shown to be similar in accuracy to assessments based on other measures. It is useful to have owners of diabetic dogs document their assessments on a standardized form, so they can provide a consistent and complete history of the dog’s response to treatment. Stable or increasing body weight, improved quality of hair coat and skin, and improved muscle mass are indications of good control of blood glucose levels. Glucose curves are a very useful measure of how well the diabetes is controlled, but do have some limitations. Stress response or inappetance can invalidate the glucose curve and there is substantial variation from day to day in an individual dog, so the information gained from a glucose curve must be interpreted in light of other measures of glycemic control.


Follow-up visits are scheduled for the morning. For the initial follow-up visit, the owner is instructed to feed the dog as usual but to wait to administer the insulin injection until the office visit. At the visit, the owner administers insulin under observation by the veterinarian or technician, so that any problems with insulin handling and injection can be addressed. For subsequent follow-up visits, the owner is instructed to feed the dog and administer the insulin at home as usual prior to the appointment. A blood glucose curve is obtained by measuring blood glucose concentration every 2 hours for 8 to 12 hours after administration of insulin. Most handheld glucometers are sufficiently accurate for this purpose, and the stress of obtaining the sample can be minimized by using a lancet to collect capillary blood from the inner surface of the pinna. Some owners may be able to perform this procedure at home, but substantial training is necessary to ensure accurate results.


13. What role does monitoring urine glucose levels have in the management of diabetes mellitus in dogs?

Monitoring urine glucose levels can aid in identifying dogs with poorly controlled diabetes and may aid in detecting hypoglycemia before it becomes severe enough to cause symptoms, but it should not be used as the sole criterion for adjusting insulin dosage. Insulin-induced hyperglycemia (Somogyi phenomenon) can result in prolonged hyperglycemia following hypoglycemia subsequent to an insulin overdose. The resultant glycosuria will not be distinguishable from hyperglycemia associated with an insulin dose that is too low. If the insulin dosage is adjusted based on the presence of glycosuria, hypoglycemia may be worsened in dogs with insulin-induced hyperglycemia. A negative result of testing urine for glucose does not necessarily mean that the insulin dosage needs to be reduced, because when diabetes is well-controlled there should be little or no glucose in the urine.


14. What can be learned about blood glucose control by evaluating a glucose curve?

The blood glucose concentration at its nadir and the duration of effect of the insulin are the most important information that can be learned from a glucose curve. The nadir is the lowest glucose concentration obtained during the sampling and ideally should be between 100 and 150 mg/dl. If the nadir is below 80 to 100 mg/dl, the insulin dose should be reduced and if it is greater than 150 mg/dl the insulin dose should be increased. The amount by which the insulin dose should be altered depends on the degree to which the nadir varies from the ideal. If the nadir is higher than desired, an increase in the insulin dose by 1 to 3 units is indicated.


The duration of insulin effect is the time that the blood glucose concentration remains below 250 mg/dl. The optimal duration of effect for a dog receiving once-daily insulin injections is 22 to 26 hours, while the ideal duration with twice-daily dosing is 10 to 14 hours. If the duration of effect is inadequate, administration of a longer-acting insulin is necessary. If the duration of effect of insulin administered once daily is inadequate, administering that insulin twice daily is usually sufficient. When switching from once- to twice-daily insulin administration, the once-daily dose should be reduced by 25%. Lente insulin can be administered if NPH insulin is of insufficient duration. If lente insulin administered twice daily has too short a duration of effect, protamine zinc insulin (PZI) or ultralente insulin may be administered. About 1 week after a change in insulin dose or formulation, another assessment of clinical signs should be performed and a glucose curve should be obtained and the dosage of insulin should be adjusted if necessary, as just described.

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Jul 31, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Diabetes Mellitus

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