What is diabetes?
Diabetes mellitus (DM) is a common hormone disease in older people and it is increasingly being recognized in older dogs and cats aged above 6 years. Diabetes mellitus is a chronic disorder of carbohydrate metabolism due to absolute (Type I diabetes) or relative (Type II diabetes) lack of insulin. In dogs, Type I diabetes is the most common while Type II diabetes is rare.
Insulin is the hormone that keeps blood sugar (glucose) at optimum levels and is produced by the pancreas. When there is a lack of insulin, sugar from food builds up in the blood and eventually starts to appear in the urine.
In dogs, females are affected twice as often as males, regardless of neuter status, while neutered males are at greater risk than intact males. In cats, obese male cats seem to be more commonly affected than female cats. Though the disease has serious fatal effects if left untreated, the majority of diabetic patients can now be treated.
What are the signs of diabetes mellitus?
Dogs or cats are presented with the following clinical signs:-
Drinking excessive water (Polydipsia)
Urinating excessively (Polyuria).
Excessive appetite (polyphagia)
Weight loss
Sugar detected in urine (glycosuria)
Occasionally sudden blindness due to Cataract or Diabetic retinopathy (rare).
Ketosis (Ketotic diabetes/Diabetic ketoacidosis):-
Ketosis
Lack of appetite (anorexia).
Vomiting.
Dehydration.
Acetone odour to the breath.
Abdominal pain.
8. Non-ketotic diabetes (Hyperosmolar diabetes mellitus /syndrome):
Weakness.
Lack of appetite (anorexia).
Vomiting.
Lethargy.
Obtundation/coma.
Why do dogs get diabetes?
Both dogs and cats can either be born with diabetes or acquire it in the course of their life. Some breeds of dogs and cats are more prone to diabetes due to their genetic make-up, however, any dog or cat can be affected in the course of their lifetime. Most diabetic dogs suffer from Type I diabetes or insulin-dependent diabetes, which is characterized by the permanent inability to produce insulin, while the majority of cats suffer from Type II diabetes (”adult-onset diabetes” or “insulin-resistant diabetes”).
The main probable causes of Type I diabetes include:-
Immune-mediated cause (though this is not firmly established).
Genetic implications, e.g. certain breeds are predisposed to diabetes.
The main probable causes of Type II diabetes include:-
Diabetogenic drugs, ie, drugs that induce type II diabetes e.g. steroids, diuretics, some heart medications, some antibiotics,
Hypothyroidism
Inactivity
Hows is diabetes diagnosed?
Persistent sugar (glucose) in urine (glycosuria).
Ketones detected in urine (Ketonuria) if Diabetic ketoacidosis.
Presence or absence of urinary tract infection (culture recommended).
Persistent blood glucose levels (>9 mmol/l) - hyperglycaemia
Increased liver enzymes.
Increased cholesterol.
Identification of exocrine pancreatic disease (trypsin-like immunoreactivity (TLI test) and Canine pancreatic lipase immunoreactivity (cPLI) test.
Elevated serum fructosamine (>500 mmol/l).
X-Rays (Radiography)
Due to fatty infiltration, abdominal x-rays often show generalised liver enlargement (hepatomegaly).
What are the risks associated with diabetes mellitus?
1) Anaesthesia: Diabetic patients are always at risk of death after major surgery and have a higher incidence of co‐existing disease. Improving sugar control in both the short and long term improves the outcome of surgery. Therefore, half of the usual insulin dose is administered before surgery, and dextrose fluid is administered intravenously during the procedure.
2) Glucocorticoids (steroids): Steroids antagonise the effects of insulin, and the dose may need to be adjusted to prevent ketosis.
How is diabetes treated?
Diabetic dogs require regular insulin injections for life to control their blood sugar levels. These injections are given on a regular basis (usually once or twice daily) immediately after diagnosis and stabilisation.
The dog's diet will also have to be carefully controlled and all titbits excluded from the diet. Successful management of diabetes requires that feeding times, exercise, and injections are all carefully coordinated.
Why do diabetic dogs need insulin injections?
In humans, Type II diabetes can be controlled by a change in diet. Dogs do not get this type of diabetes as they always suffer from type I diabetes, which is insulin-dependent. Insulin is a protein, and if given orally as a tablet, can be digested by the acid in the stomach, and the insulin would have no effect.
The normal injections are given under the skin and do not hurt. It is better to feed the dog or the cat after administering the injection. Pets quickly learn that once they have had their injection, they get their food and are happy to stand still for the jab.
What are the complications of diabetes mellitus?
There are several important complications that occur during diabetes illness:
1) Low blood sugar (hypoglycemia) - Hypoglycaemia can lead to permanent brain damage. Symptoms develop rapidly and include restlessness, confusion, tremors, twitches, convulsions or coma. Sugar should be given by mouth, dissolved in water or as lumps. If the pet is still awake it may be offered food and should eat voluntarily. Once these signs develop a veterinarian should be contacted immediately.
2) High blood sugar (hyperglycemia) - This usually develops more gradually and the pet becomes unwell over a number of days. Development of antibodies would also result in persistent hyperglycemia just as food refusal and vomiting does encourage hyperglycaemia and lack of efficacy of the insulin being used.
3) Cataract
Cataract in Diabetic patients is caused by increased amounts of glucose in the lens, that is converted into insoluble sugar (sorbitol) in the lens which cannot be converted to fructose that diffuses out of the lens.
The osmotic potential of sorbitol encourages water influx into the lens. This causes the lens to swell, disrupting the normal structure of fibres and other metabolic changes occur leading to blindness.
4) Diabetic glaucoma
As diabetic cataracts progress, they often cause inflammation within the eye known as “lens-induced uveitis”. This inflammation is often the cause for other related complications such as the development of glaucoma or retinal detachments (diabetic retinopathy).
5) Diabetic retinopathy
Diabetic retinopathy is a complication of diabetes mellitus that affects the eyes. Diabetic retinopathy is caused by damage to the blood vessels in the tissue at the back of the eye (retina). Poorly controlled blood sugar is a risk factor and leads to blindness. Mild cases may be treated with careful diabetes management. Advanced cases may require laser treatment or surgery.
6) Hyperlipidaemia
A condition in which there is raised blood concentration of fat particles (lipids) in the hungry (>12 hours) patient. Hyperlipidemia is a consequence of hyperglycemia and alters the membrane fatty acid composition making cell membranes less fluid and deformable.
Hyperlipidaemia causes osmotic fragility that has been shown to shorten RBC lifespan. Examples of lipids include cholesterol and triglycerides. These substances can deposit in blood vessel walls and restrict blood flow. This creates a risk of heart attack and stroke.
8) Diabetic dermatopathy
Diabetic dermopathy is an entity that is poorly understood and commonly observed clinically in humans than in pets. Diabetic dermatopathy is linked with retinopathy, neuropathy and nephropathy. Bacterial and yeast-induced dermatitis and otitis develop in dogs with diabetes mellitus having a preexisting allergic condition, history of prior corticosteroid administration, or concurrent endocrinopathy that may be a more likely cause of dermatologic problems than diabetes mellitus alone.
9) Diabetic glomerulonephropathy
Diabetic glomerulonephropathy is a potentially serious complication of diabetes mellitus but extremely rare in the naturally occurring canine disease. In humans, diabetic nephropathy is a leading cause of morbidity and mortality in chronically diabetic patients. In humans, it is characterized clinically as a triad of hypertension, proteinuria (proteins in the urine) and eventually renal impairment and disease. In diabetic dogs proteinuria (proteins in the urine) is relatively common but is not associated with hypertension (also relatively common in diabetic dogs) or duration of diabetes nor does there appear to be an increased prevalence of chronic kidney disease. The observed proteinuria in diabetic dogs may represent an alternate pathology to that described in diabetic human patients.
10) Diabetic neuropathy
High levels of glucose in diabetic patients lead to changes that also affect proteins causing far-reaching effects that include nerve injury through the damage of nerve sheaths slowing nerve conduction referred to as diabetic neuropathy. It is more common in cats than in dogs.
What are the dietary considerations?
Insulin therapy provides the main treatment for most diabetic dogs, however, the management of other factors including diet and exercise influence the overall glucose control. A consistent dietary program is essential, the same diet fed at the same time every day. Minimizing increased blood glucose after eating and avoiding sugar fluctuations in the body is the principal goal of dietary therapy. Most fibre-rich diets, particularly insoluble fibre, low-carbohydrate, low-fat, or combination content result in improved glucose control. If diabetes is difficult to regulate, fibre content is increased and the diets made palatable to ensure predictable consumption. Equal-sized meals should be offered every 12 hours (with insulin administration), with overweight dogs requiring weight reduction programs, as obesity contributes to insulin resistance.
The nutritional requirements of any concurrent illness, e.g., liver, kidney or heart disease, for which there is a known dietary therapy should take precedence in diabetic cases. Dry or canned foods are appropriate but semi-moist diets should be avoided as they contain large amounts of simple sugars that can result in large increases in glucose concentrations after eating.
Obesity and poor body condition are usually associated with poor diabetic stability and need appropriate management in individual dogs. Increased fibre and restricted fat diets are beneficial in at-risk cases. To prevent protein breakdown and loss of weight, the diet should provide protein of adequate quantity and quality.
Diabetic glomerulonephropathy, whilst common in humans, is rare in dogs and restricted protein diets are therefore not considered necessary. If the diet is balanced and complete and fed in an appropriate quantity for optimal body condition, there is no need for additional vitamin and mineral supplementation.
Other considerations for diabetes therapy?
All Identified concurrent disorders should be addressed adequately. These may include:
Dental disease.
Concurrent endocrinopathies (hormone diseases).
How is diabetes monitored in dogs and cats?
Regularly monitoring the diabetic patient is essential to make sure it doesn't gain or lose weight. Blood samples from the diabetic patient may be taken in intervals to ascertain the proper functioning of the major organs, i.e. the liver and the kidneys.
Every fortnight, a serial blood glucose curve is performed to establish stability (a blood sample is done every 2 hours throughout the day at home using a hand-held glucometer). If problems develop, the glucose curve is repeated to assess insulin response. If the insulin needs to be adjusted, it is cautiously increased (10-20%) in hyperglycaemia or decreased (25%) in hypoglycaemia. Levels of blood Fructosamine can also be measured with levels <400 mmol/l being a good control and levels >500 mmol/l common in newly diagnosed cases or where there is poor control. Glycosylated haemoglobin when measured shows good control if it is 4-6% and poor control if it is >7%.
Prevention
Early ovariohysterectomy is helpful in susceptible animals. It is advisable that all-female dogs are neutered if they are not going to have puppies, and most certainly if the dog already has diabetes, as the disease will be more easily controlled. Sterilization of bitches should be done once stabilized. High concentrations of progesterone and growth hormone in cycling bitches antagonize insulin. Prolonged or recurrent episodes of insulin resistance following multiple estrus cycles may lead to permanent damage to insulin-producing cells (beta cells) within the pancreas.
There is no evidence that canine diabetes can be prevented in dogs or cats, however, modulating associated risk factors i.e., obesity, inactivity, hormone diseases, may influence risk for development.
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