Gemma Gaitskell
Dr Gemma Gaitskell (BVetMed MSc MRCVS, Royal Veterinary College, London)
 
Pet Insulin

Diabetes mellitus is a metabolic endocrine disorder that many people are familiar with due to the large number of humans who suffer from it. However, it can also affect dogs. It is a chronic disease, which affects the bodie's ability to use glucose as an energy source.

This inability is caused by either a relative or absolute lack of the hormone insulin, depending on the type of diabetes affecting the dog. Despite its gravity, diabetes mellitus can be effectively managed by providing treatment, allowing dogs to live a happy healthy life.

What is Diabetes Mellitus?

Dog getting injection

Diabetes mellitus is a chronic disease that is caused when the body becomes intolerant to glucose due to insulin deficiency. This deficiency can be relative or absolute depending on the sub-type of diabetes mellitus. In the long-term diabetes affects all body systems, however the disease is principally a disorder of carbohydrate metabolism and breakdown.

Insulin is a small polypeptide hormone which is produced by the beta cells located in the islets of Langerhans in the pancreas. The pancreas is a small, but essential organ, which is found in the abdomen near to the stomach. It produces enzymes that are vital for digestion as well as insulin. In healthy dogs rising blood glucose levels after eating stimulate the release of insulin. If blood glucose levels are too low its secretion is inhibited. The body needs glucose as an energy source.

After the process of insulin release has been stimulated insulin binds to receptors on the surface of cells and this allows them to take in glucose and store it either as glycogen or fat which can be used as a future energy source. This uptake by certain cells means that the amount of glucose circulating in blood is reduced and blood sugar levels return to normal. Any interruption to the process of insulin release or cell binding can produce diabetes mellitus.

There are several hormones that influence and reduce the effects of insulin and cause blood glucose levels to rise. These hormones include corticosteroids, glucagon, growth hormone, progesterone, oestrogen and catecholamines. A variety of conditions that cause high levels of these hormones as seen in many endocrine diseases can cause diabetes mellitus.

Types of Diabetes Mellitus

Type 1 or insulin dependent diabetes mellitus where there is an absolute lack of insulin

This is the most common form of the disease accounting for nearly all cases of diabetes mellitus in dogs. This type of diabetes mellitus is caused when the beta cells no longer produce insulin due to degeneration or disruption, which is often linked to pancreatic disease. It is thought that there may be an immune response that causes the destruction of these cells – although some studies have shown conflicting results about this theory.

Type 2 or non-insulin dependent diabetes mellitus where there is a relative lack of insulin

In this type of diabetes mellitus, the interruption in the process is where tissues and their cells fail to respond to insulin, known as resistance. The receptors on cells become less sensitive to the hormone or down-regulated. In the early stages of this type of diabetes mellitus, the changes are reversible. However, eventually the chronic over-stimulation of the beta cells in the pancreas can cause them to become permanently damaged, which ultimately leads to a reduction in the amount of insulin they produce. This type of diabetes mellitus is more common in obese cats than dogs, but when seen in dogs they are usually older and overweight.

Type 1 Vs. Type 2

The type 1 and 2 classification is more widely used in humans, but it is more difficult to use this classification in dogs as the exact cause and significance of an autoimmune response are still unclear, so the insulin dependent or non-insulin dependent terminology is used more often.

Once the beta cells in the pancreas have been severely damaged diabetes is likely to be insulin dependent, whereas in the early stages of the disease the type of diabetes is often dependent on the level of insulin resistance caused by obesity, other illnesses, endocrine diseases or medications.

How Do Dogs Get Diabetes Mellitus and When Does it Occur?

Dogs get diabetes mellitus when there is a disruption in the way insulin should function cells are not able to use glucose and convert it into energy. This means that fat and protein stores have to be broken down to produce energy, causing muscle wasting, depletion of fat reserves as well as an overall loss of weight despite eating the same and in most cases more to make up for the lack of energy.

Fats are broken down and converted into ketone bodies – a process which would usually be limited by insulin. The release and production of glucose from tissues continues where it would normally be inhibited by insulin and this, combined with glucose from the diet causes the excessively high blood sugar levels seen in diabetes mellitus. As blood glucose levels rise they reach a point where the kidney can no longer reabsorb all the glucose and it is eventually lost in the urine, which also unbalances the amount of water that is normally lost in urine, causing dogs to urinate more and drink more due to increased water loss.

When diabetes mellitus is unstable, dogs can develop diabetic ketoacidosis. This can occur anytime from days to months after clinical signs become apparent. Hormones which work against insulin, in particular glucagon are produced in excess and cause an increase in the production of ketones and glucose. As levels of glucose and ketones rise more water is lost in urine alongside electrolytes, resulting in dehydration and this causes effects on the heart, kidneys and blood supply to tissues.

Ketone bodies are acidic and this produces a metabolic acidosis, alongside the lactic acid which is produced by tissues suffering from a reduced blood supply as well as further water losses from vomiting and diarrhoea. Diabetic ketoacidosis is extremely dangerous and immediate treatment must be provided to rehydrate the dog, correct electrolyte imbalances and the acidosis.

Which Types of Dog and Breeds Are Most Commonly Affected by Diabetes Mellitus?

Diabetes mellitus is more commonly seen in middle aged to older dogs, aged 6 plus and older dogs which are overweight, although it can be seen in dogs of any age. It is also more likely for female dogs to be affected than male dogs and certain breeds seem to have a disposition to the condition, although any breed can be affected. Often small breeds seem to have a higher incidence of the disease than others. Some of these more commonly affected breeds include:

Symptoms of Diabetes Mellitus in Dogs

The following are some common clinical signs of diabetes mellitus that are often seen in dogs:

  • An increase in the amount of water drunk and therefore amount of urine produced
  • Weight loss despite eating an increased amount of food
  • Eye conditions such as cataracts and retinopathy
  • Vomiting
  • Anorexia
  • Weakness and lethargy
  • Abdominal pain
  • Dehydration

There may be a seasonal pattern in diagnosis – a scientific study found that there were twice as many diagnoses from November to January as there were from July to September.

Diagnosis of Diabetes in Dogs

In addition to the clinical signs evident in a dog suffering from diabetes mellitus, the disease is diagnosed using a range of diagnostic tests, including:

  1. Analysis of the Urine – Urinalysis shows the abnormal presence of glucose and ketones in the urine. There may or may not also be signs of a urinary tract infection that can be ruled out by a bacterial culture of the urine.
  2. Blood Tests – Blood biochemistry shows elevated levels of glucose in the blood, even when the dog has been fasted, as well as increased levels of liver enzymes and cholesterol.
  3. Radiography – X-rays taken of the abdomen often show an enlarged liver due to fat deposition.

There are several other diseases which can cause a dog to drink and urinate more and it is important that these are ruled out during the diagnostic process. These differential diagnoses which can cause some similar symptoms to diabetes include:

  • Kidney disease
  • Liver disease
  • Diabetes insipidus
  • Psychogenic polydipsia
  • Hypercalcaemia
  • Hyperadrenocorticism

When diagnosing diabetes it is also important that any drugs that a dog is currently taking are ruled out as the cause.

Can Diabetes in Dogs Be Treated?

Bulldog having his blood pressure taken

It is essential that as an owner you understand the implications and effects diabetes mellitus can have on your dog and that you attempt to cooperate with the veterinarian which is providing advice and treatment. This will generally lead to a much improved outcome. The treatment for diabetes mellitus in dogs is formed by a combination of different measures which can include:

Obesity Control

Weight loss if the dog is over its ideal weight, as this can in some cases improve sensitivity to insulin. Weight loss should be achieved by reducing the calories in the diet and increasing exercise levels.

Caloric Intake

If the dog has lost a large amount of weight the calories in its diet should be increased until it reaches its ideal weight.

Appropriate Diet Selection

Feeding an appropriate diet and avoiding any inappropriate treats and snacks and foods high in sugar. Diets which contain high levels of fibre and complex carbohydrates such as whole grains and other ingredients that are known to have a beneficial effect on blood glucose are preferable.

Insulin Replacement Therapy

There are various different types of insulin available, but most dogs need to be injected with insulin twice a day. Your veterinarian will choose the type of insulin they think is most appropriate for your dog and initially start treatment with a low dose, which will be increased if necessary. It is important that insulin is stored correctly and administered properly at scheduled times which your vet will provide advice on.

Diabetic Ketoacidosis

If a dog is suffering from severe diabetic ketoacidosis as described above it must be treated immediately as an emergency to correct the electrolyte and acid imbalances and dehydration as this can be fatal.

Other Illnesses

Additional treatment may be needed for any other concurrent disorders such as urinary tract infections, endocrine diseases and dental disease.

Oral Hypoglycaemic Medications

Although these medications are effective in humans suffering from type II diabetes mellitus they are not very effective in dogs and therefore unfortunately not a treatment option.

Treatment & Prognosis

Once treatment with insulin has been initiated dogs should be carefully monitored and then have their blood glucose re-tested by a veterinarian around 1-2 weeks later and then subsequently every 2-3 weeks after this until their blood glucose levels are stable, adjusting insulin doses as necessary. Once stable, dogs usually need check-ups at least twice a year to ensure the condition is properly under control or if they show any signs of the diabetes mellitus reoccurring.

The prognosis for dogs suffering from diabetes mellitus is good if the disease is well managed, with appropriate diet, exercise levels and insulin administration. There are some complications that are associated with the disease of which the development of cataracts, pancreatitis and an increased risk of bacterial infections are the most common. However, their chance of their occurrence can be reduced by good management.

Once diabetes mellitus is under control and blood glucose levels are stabilised a dog should begin to drink less, maintain a more consistent weight as well as appear happier with higher energy levels.

Preventing Diabetes in Dogs

At the time of writing, there are no proven measures that can prevent the development of diabetes mellitus. Spaying female dogs may decrease the risk and also help stabilise dogs suffering from diabetes mellitus as the high levels of progesterone present in the body during dioestrus (in-between seasons) can contribute to insulin resistance.

If a dog is known to suffer from diabetes, it should not be bred from. Ensuring dogs do not become overweight is also an important measure that can be taken to reduce the risk of non-insulin dependent or type 2 diabetes mellitus developing.

The Importance of Early Treatment of Diabetes

Diabetes mellitus is a disease which can have severe consequences if it is not recognised promptly, well-managed and controlled. That said, proper treatment can effectively control the condition and allow dogs to lead a normal good quality life.

References

  • Davison, L.J., Herrtage, M.E. & Catchpole, B. (2005). Study of 253 dogs in the United Kingdom with diabetes mellitus. Vet Rec: 156, 467-471.
  • Davison, L.J., Catchpole, B., Kennedy, L.J., Barnes, A., Thomson, W. & Ollier, W.E. (2003). Research into canine diabetes mellitus. Vet Rec: 152 (5), 148.
  • Fleeman, L.M. & Rand, J.S. (2003). Evaluation of day-to-day variability of serial blood glucose concentration curves in diabetic dogs. JAVMA: 222 (3), 317-21.
  • Mattin, M.J., O'Neill, D.G., Church, D.B. & Brodbelt, D.C. (2013). Canine diabetes mellitus: prevelence, risk factors and survival. In: Scientific Proceedings, British Small Animal Veterinary Association Congress, Birmingham: p 568.
  • Merck and Co. (2016). The Merck Veterinary Manual (11th Edition).
  • Niessen, S.J., Powney, S., Guitian, J., et al. (2012). Evaluation of a quality-of-life tool for dogs with diabetes mellitus. JVIM: 26 (4), 953-961.
  • Rucinsky, R., Cook, A., Haley, S., Nelson, R., Zoran, D.L. & Poundstone, M. (2010). AAHA diabetes management guidelines. JAAHA: 46 (3), 215-224.

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