Diabetes Mellitus

Diabetes Mellitus

What is Diabetes Mellitus (DM)?

Diabetes Mellitus is a complex metabolic disorder in dogs which is relatively common. It occurs in middle-aged to older dogs and has reported worldwide prevalence ranges from 0.3% to 1.3%.

Entire females are affected twice as often as males and there is an increased incidence in small breeds, however any breed can be affected.

Diabetes Mellitus is caused by a relative or absolute deficiency in the hormone insulin, which is required to regulate glucose in the body. In the absence of insulin the dog will become hyperglycaemic.

Diabetes Mellitus can affect dogs, cats and other animals (including apes, pigs and horses) as well as humans.

Breeds prone to Diabetes Mellitus (DM)

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There is an increased incidence of DM in small breeds, however any canine breed can develop this disease.

Breed examples at a higher risk of developing DM include;

  • Miniature Poodles
  • Miniature Schnauzers
  • Bichon Frise
  • Dachshunds
  • Cairn Terriers
  • Beagles
  • Schnauzers
  • Samoyeds
  • Keeshonds
  • Australian Terriers
  • Fox Terriers

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Pathogenesis

Diabetes mellitus (DM) also known as "sugar diabetes" is a common endocrine disease which is seen in middle aged dogs.

This metabolic disorder results in either a decrease in the production of insulin, or where the insulin doesn't work as effectively as it should.

Insulin is a hormone made by the pancreas.

Hormones are chemical messengers secreted into the blood which transports the hormones to specific organs and tissues to action a bodily process.

Metabolism refers to the conversion of food nutrients into energy, to power the body's cells. This is an ongoing process which involves a "glucose - insulin" connection.

Glucose is an essential fuel for the body's cells. The body breaks down some of the nutrients into glucose, which is a simple sugar and absorbed into the blood from the intestines to be transported throughout the body. It's an important source of energy for certain body cells and organs.

Insulin is produced by the beta cells in the areas of the pancreas called the "Islets of Langerhans" and is released when the blood glucose is too high. The insulin attaches to special receptors on the cells of muscles and fat, "acting like a key in a lock", opening the door to allow glucose to enter the cells.

In DM, the "glucose - insulin" connection isn’t working as it should. This disease is seen in dogs in two forms;

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Type 1

Insulin-deficiency diabetes; is when the dog’s body isn’t producing enough insulin. This can be a result of damage or poor functioning of the pancreas. 

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Type 1 insulin-deficiency diabetes is the most common type of diabetes in dogs.

Type 2

Insulin-resistance diabetes; is when the pancreas is producing insulin, but the dog’s body is unable to utilise the insulin as it should.

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Female dogs can also develop temporary insulin resistance whilst in season or during pregnancy.

The cells aren’t responding to the insulin’s “message”, so glucose isn’t being pulled out of the blood and into the cells.

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Type 2 insulin-resistance diabetes is seen more commonly in older, obese dogs.

Impact of Type 1 + Type 2 DM

Both types of DM have the same negative effects on the dog's body. The glucose levels in the blood rise, but the cells are starved of energy due to the lack of production of insulin.

Muscle cells and certain organ cells are deprived of glucose and in response, the cells have to find other sources of energy. The cells switch from using glucose to breaking down fats and proteins to use as alternative energy.

Increased glucose levels in the bloodstream causes damage to many organs including the kidneys, eyes, heart, blood vessels and nerves.

When the blood glucose concentrations rise above a certain point more glucose passes through than can be recovered and glucose appears in the urine (glucosuria). This creates osmotic diuresis with excess water loss and increased thirst.

Fat metabolism produces ketones which build up in the blood. If the ketone levels in the blood get very high, they may then appear in the urine (ketonuria).

High levels of ketones in the blood can be very dangerous.

Other risk factors for DM in dogs include concomitant diseases such as;

  • Hypothyroidism
  • Obesity
  • Hyperadrenocorticism

Other hormonal or iatrogenic insulin-resistance triggers include;

  • Diestrus
  • Medications such as steroids or progestins

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Dogs most commonly develop insulin dependant DM, similar to Type 1 DM in people.

DM affects entire females twice as often as males.

Predisposing factors which increase the risk of developing DM include;

  • Age; DM can occur at any age, however it most commonly occurs in middle-aged to older dogs. Most dogs that develop DM are 5 years or older when diagnosed
  • Gender; entire female dogs are twice as likely as male dogs to develop diabetes
  • Pancreatitis; chronic or repeated pancreatitis (inflammation of the pancreas) can eventually cause extensive damage to the pancreas, resulting in DM
  • Obesity; contributes to insulin-resistance Type 2 diabetes and is a risk factor for pancreatitis, which can lead to DM
  • Steroid medications; long-term use of these medications can cause DM
  • Hyperadrenocorticism; this is when the body produces too much of a hormone called cortisol (steroid), which can also lead to DM
  • Other health conditions; some autoimmune disorders and viral diseases are also thought to possibly trigger DM
  • Genetics; DM can occur in any breed or mixed-breed, and research shows that genetics can play a role in either an increased or decreased risk

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A 2003 research study looking at DM identified that mixed-breeds and pure breeds have a similar incidence of developing diabetes. However, amongst the pure breed population, different breeds may vary in susceptibility. Some pure breeds have a very low risk, whereas others have a higher risk.

Clinical Signs

  • Polydipsia (increased thirst)
  • Polyuria (increased urination)
  • Polyphagia (increased hunger)
  • Weight loss despite polyphagia
  • Persistent or recurrent urinary tract infections
  • Decreased muscle mass

Advanced Clinical Signs

  • Anorexia
  • Vomiting
  • Diarrhoea
  • Depression
  • Weakness
  • Collapse

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Diabetes Mellitus can become “complicated” and lead to a state called diabetic ketoacidosis (DKA). This usually occurs if a secondary disease process is present, such as chronic pancreatitis, or if a diagnosis of diabetes mellitus is delayed. This can result in a long-term increase in plasma glucose levels.

Additional Clinical Signs

  • Cataracts (leading to blindness)
  • Hepatomegaly (enlarged liver)
  • Urinary tract infections (UTI's)
  • Seizures
  • Kidney failure
  • Peripheral neuropathy (rare)
  • Ketoacidosis; this is a potentially life-threatening acute condition. It can be accompanied with rapid breathing, dehydration, lethargy, vomiting, or sweet-smelling breath. These clinical signs can be triggered by factors such as stress, surgery, fasting, infection, or an underlying health condition combined with low insulin levels.

Uncontrolled Diabetes Mellitus can have devastating effects on other organ systems in the dog. Early diagnosis and appropriate treatment are key to the long term management of this disease.

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Clinical Tip; if you have picked up any clinical signs or the owner has reported any to you during a session that suggests a dog may be diabetic you should refer them back to the vet immediately.

Diagnostic Tests

  • Blood Tests; haematology, biochemistry to check organ function and fructosamine which shows blood glucose concentrations during the previous few weeks.
  • Urinalysis; dipstick test to check for the presence of glucose and ketones. Urine culture analysis to check for urinary tract infections (UTI's) is important. This is due to 35% of UTI's being "microscopically silent". This means that no bacteriuria or white blood cells (WBC) are present in dogs with DM.
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Diabetes Mellitus Treatment + Management

The majority of dogs with DM can be successfully stabilised and will remain so for long periods of time. However, a significant minority will either become unstable again or will be difficult to stabilise from the outset.

The most common cause for instability of DM is failure in the daily management of the patient.

The main goal in the treatment of DM is to eliminate the owner-observed clinical signs by limiting blood glucose fluctuations and maintaining near-normal blood glucose levels. These are achieved through correct;

  • Insulin administration
  • Dietary therapy
  • Exercise
  • Management / prevention of concurrent inflammatory, infectious, neoplastic or hormonal diseases

The definitive therapy for DM in dogs is insulin administration. This replaces the deficiency caused by the lack of functional pancreatic beta cells. Treatment requires a short-acting insulin, with a rapid onset of action that degrades quickly. This can be administered intravenously, intramuscularly, or subcutaneously.

Additional Information

Insulin Therapy

Insulin is classified according to its promptness of action, duration and intensity of action;

  • Short acting; rapid onset of action (minutes), short duration of effect (hours) and has a high potency
  • Intermediate acting; used on a twice daily basis and administered via a subcutaneous injection. Intermediate duration effect in dogs (lasting 6-8 hours) and moderate potency
  • Long acting; occasionally used in feline DM. It has a long duration of effect (usually between 12 and 18 hours)and is the lowest potency of all the insulin types

Different Types of Insulin

Human insulins are either porcine, bovine or recombinant (biosynthetic) human. Dogs generally respond better to porcine insulin, whereas cats respond best to bovine insulins. Combinations exist and recombinant human technology is becoming more and more popular.

Veterinary Insulin

The only insulin registered for veterinary use is Caninsulin, which is porcine. It is regarded as an intermediate acting insulin in cats (usually needing twice daily administration) and a longer acting insulin in dogs, requiring once daily administration.

Generally, this is the insulin that most veterinary patients are started on.
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Dietary Therapy

The goals of dietary therapy are to optimise bodyweight. This is achieved by feeding a diet that has appropriate protein and carbohydrate levels, fat restriction, and calorie and portion control.

Weight loss in obese patients and stopping DM associated weight loss, are treatment goals for diabetic canine patients.

Consistency in timing of feeding and managing protein and carbohydrate intake is recommended to minimise postprandial hyperglycemia.

Exercise

Exercise is proven to be beneficial for diabetic dogs as it helps to lower insulin requirements and provide better glycemic control.

Daily walking or play exercise for dogs with DM can be an effective ancillary treatment to help achieve glucose control using lower doses of insulin.

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Hypoglycaemia; occurs with sudden increases of insulin dose, sudden inappetence, strenuous exercise or using insulin twice a day when the duration of effect overlaps slightly and the previous injection has additive effects on the later injection.

Clinical signs include; weakness, shivering, tachycardia and ultimately seizures (due to neuroglycopaenia). Treatment must be prompt and can be administered by mouth or intravenously.

Summary

DM is a treatable condition, however it can be complicated. It requires a committed effort by the vet and owner and there are many factors that impact the diabetic state which include;

  • Body condition
  • Weight management
  • Mobility problems
  • Fitness levels
  • Diary management of their therapy appointments in relation to their feeding management and insulin regime

Each canine patient requires an individualised treatment plan, frequent reassessment, and modification of the treatment plan based on the patient’s responses, behaviours and health checks.

Using clinical reasoning, linked to current scientific evidence on DM, will support clinical choices and lead to safe and effective practice.

Conservative treatments utilising a multimodal approach

For most diabetic dogs, insulin therapy will improve clinical signs soon after initiation. However, it may take several weeks for the animal to fully adjust to insulin therapy and the average time for initial DM control is 4 - 6 weeks.

Conservative strategies may include;

  • Bodyweight control + monitoring
  • Nutritionally balanced diet
  • Exercise modification (little + often)
  • Use a well fitted "Y" shaped harness which could be padded
  • Avoid stressful situations
  • Avoid warm environments
  • Provide fans / cooling mats in warmer months
  • Exercise at appropriate times of day in warmer months, early morning / late evening
  • Physiotherapy
  • Hydrotherapy

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Clinical Tip: Routine is the key to effectively managing dogs with DM. Avoid strenuous exercise and stressful environments by using Movement Enrichment Techniques. Respond positively to each dog's series of feedback signals in the clinic. Use appropriate diary management, dynamic risk assessment and ongoing health checks during your assessment, re-assessment and treatment techniques.

References

Catchpole, B., Ristic, J.M., Fleeman, L.M. et al. Canine diabetes mellitus: can old dogs teach us new tricks?. Diabetologia 48, 1948–1956 (2005). https://doi.org/10.1007/s00125-005-1921-1

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