A 7-year-old female (entire) Husky presented to the clinic with weight loss despite a good appetite. The owner reported that the dog had been drinking more than usual (polydipsia) and was also urinating more frequently (polyuria). Vaccination and worming were up to date. On clinical examination the dog had a body condition score of 4/9 and had lost 7 kg since the previous examination 1 year ago. No other abnormalities were found on clinical examination. Tests to aid diagnosis were performed including haematology and biochemistry blood tests, which revealed hyperglycaemia with a blood glucose of 27.6 mmol (3.3–6.1 mmol) and urinalysis, which indicated glucosuria and ketonuria.
Hyperglycaemia refers to abnormally high levels of glucose (a simple carbohydrate sugar) in the blood. Glucose is a major source of energy for the body and insulin, a hormone produced and released by the pancreas, plays a key role in maintaining normal sugar levels. Table 1 indicates the potential causes of hyperglycaemia in dogs.
Table 1. Potential causes of hyperglycaemia in dogs (Davison, 2018)
| Stress — cortisol and adrenaline response |
| Diabetes mellitus |
| Other endocrine causes of insulin resistance, e.g. hyperadrenocorticism, acromegaly, dioestrus |
| Iatrogenic causes, i.e. total parenteral nutrition, exogenous glucocorticoids |
| Pancreatitis |
| Neuroendocrine tumour, e.g. glucagonoma |
| Exogenous pharmacological agents, e.g. ketamine, medetomidine and propranolol |
| Other causes of insulin resistance, i.e. infection, inflammation, hyperlipidaemia and hyperthyroidism |
The case above highlights a presenting history, findings from clinical examination and results of diagnostic tests that indicate canine diabetes mellitus. Hallmark signs of this disease are polyuria and polydipsia with concurrent weight loss. If this case had been left untreated, clinical signs would most likely have progressed to inappetence, lethargy, vomiting and, in some cases, the development of ketoacidosis, which is a serious and life-threatening complication of diabetes (Davison, 2018).
Aetiology and pathogenesis
Canine diabetes mellitus is a complex endocrinopathy, with a pathogenesis that varies amongst individuals, but is clinically similar in most dogs to Type I diabetes in humans (Shields et al, 2015; Harrington et al, 2017). The aetiology and pathogenesis of the disease remains poorly understood (Shields et al, 2015); however, irrespective of the underlying aetiology, diabetes mellitus is reported to occur as a result of the interplay between environmental and genetic factors (Mattin et al, 2014).
Diabetes mellitus has been reported to affect approximately one in 300 dogs (Mattin et al, 2014), with breeds such as the Samoyed and Tibetan terrier being over-represented in diabetic cohorts (Catchpole et al, 2013) suggesting an underlying genetic predisposition. It is not clear, however, whether the pathogenesis of the disease varies between or within breeds (Gilor et al, 2016). The average age of dogs that develop diabetes mellitus is approximately 7 years (Davison et al, 2005). There are many studies that have looked at gender differences and the effects of neutering in the canine population; however there appears to be no general consensus of agreement with regards to the effects of neutering and an association with the development of diabetes mellitus (Guptil et al, 2003; Fall et al, 2007). Research has reported that entire females may develop progesterone-induced diabetes mellitus (Fall et al, 2010), which results from the insulin antagonistic effects of progesterone and mammary gland-derived growth hormone (Selman et al, 1994). A study conducted by Fall et al (2010) investigated the onset of diabetes mellitus associated with dioestrus in Elkhounds, and showed that there was a link; it would therefore be deemed prudent to ask owners when their dog's last season was. If an entire bitch is diagnosed with diabetes mellitus, she should be spayed as soon as possible in order to help stabilise the condition (Ackerman et al, 2018). Classification regarding the pathogenesis of the disease has been attempted (as shown in Table 2) however there is still no general consensus regarding this.
Table 2. Classification of canine diabetes mellitus (Catchpole et al. 2005)
| Classification | Aetiology/Pathogenesis | Disease processes thought to be involved |
|---|---|---|
| Primary insulin deficiency diabetes (IDD) | Progressive loss of pancreatic beta cells; aetiology unknown | Congenital beta cell hypoplasia/abiotrophy |
| Beta cell loss associated with exocrine pancreatic disease | ||
| Immune-mediated beta cell destruction | ||
| Idiopathic disease | ||
| Primary insulin resistance diabetes (IRD) | Usually results from antagonism of insulin function by other hormones | Dioestrus/gestational diabetes |
| Hyperadrenocorticism | ||
| Secondary to other endocrine disorders | ||
| Acromegaly | ||
| Iatrogenic | ||
| Synthetic glucocorticoids | ||
| Synthetic progestogens | ||
| Glucose intolerance associated with obesity |
Whatever the classification, the general effects of diabetes in dogs are:
- Muscle cells and certain organ cells are deprived of glucose and thus the body starts to break down its own fats and proteins to use an alternative fuel
- High levels of glucose in the bloodstream will eventually cause multi-organ damage, e.g. damage to the kidneys, eyes (cataracts), heart, blood vessels and/or nerves.
Support and advice for owners
Building a good rapport and relationship with the owner will be key to a successful outcome in these cases. Investigation and treatment of canine diabetes will require considerable investment from owners. This will include both financial commitment and considerable time and effort for owners monitoring the dog and working closely with the veterinary team. Veterinary nurses can play a key role in both educating owners with diabetic dogs and with supporting them; and where possible, specific diabetic veterinary nursing clinics can provide significant support to owners (Ackerman et al, 2018).
It is important that owners are aware of the strict routine that dogs will need in order to manage the disease. The aim of treatment is to minimise hyperglycaemia and its effects, while avoiding hypoglycaemia (Ackerman et al, 2018). In addition, quality of life of both the dog and the owner must be a key consideration. While in most cases the majority of dogs will do well once diagnosis and a treatment regimen has been established, some cases are not straightforward, such as those linked to ketoacidosis, and will require prolonged periods of hospitalisation, and intensive ongoing management (Davison, 2018). The most common cause for instability in dogs is poor daily management (Schoeman, 2011) (Figure 1). In all cases, due to the aetiology and pathogenesis of the disease being varied, it is important that the underlying cause of diabetes in each individual dog is explored as this will affect prognosis and ensure that treatment is tailored and owner expectations are considered. In a study published by Mattin et al (2014) the median survival time was 17.3 months following diagnosis; however increasing age and a concurrent diagnosis of pancreatitis were associated with a decreased survival time. Dogs that are insured are reported to have increased survival following diagnosis, and it has been suggested that while diagnosis is low-cost, there is a high long-term cost that requires both financial and emotional commitment from owners due to the need for lifelong treatment (Mattin et al, 2014). With this in mind, it is not surprising therefore, that in some cases, owners will make the decision that treatment is not a viable option and may therefore decide to euthanase the dog. Consideration of owner quality of life is key, as poor quality of life may easily lead to euthanasia of the dog (Ackerman et al, 2018).
Record keeping
It is vital that owners accurately record what is happening with their dog on a daily basis. This could be by way of a written diary, computer spreadsheet or via an App (RVC Pet Diabetes App/MSD Animal Health Pet Diabetes Tracker App). Records should include the time, dose and type of insulin used; clinical, weight and behavioural information; and urine and blood glucose results and their timing (Ackerman et al, 2018). Quality of life should also be recorded; however this could be challenging for owners to do, given the owner–dog bond.
Diet, feeding and exercise
Feeding regimens will need to be tailored to the individual dog and also to the lifestyle of the owner. It is vital, however, that the same amount of food (of the same type) is fed at the same time every day. There are many different commercially available diets on the market specifically tailored for diabetic dogs; however many of these diets are not suitable for underweight dogs as they will not meet the calorie needs of the dogs. Ideally, they should contain up to 30% metabolisable energy (complex and low glycaemic-index carbohydrates) while being low in simple sugars and fat (Elliott et al, 2012). This is particularly important for dogs that have pancreatitis or are lipaemic. A moderate amount of fibre should also be included in the diet (Fleeman et al, 2009) and there is no need to restrict protein.
It is important that dogs eat, however, while the majority of dogs will have a good appetite, getting some dogs to eat may be challenging. Thus, timing of feeding will vary depending on each individual case (Davison et al, 2018):
- Most dogs with diabetes are typically fed twice daily, within 1 hour of each insulin injection; this is to coincide the beginning of the insulin effect with any post-prandial hyperglycaemia
- Some owners (particularly with dogs that have a poor appetite) prefer to feed before the injection so that the insulin dose can be adjusted if the dog does not eat and thus prevent hypoglycaemia
- Some owners will wait 30 minutes to an hour after the injection before they feed as this will allow the soluble component of the insulin to have an effect and thus dogs will eat better.
Exercise is an important part of management of canine diabetes and dogs should receive the same amount of exercise, at the same time each day. This means that their use of food and insulin is predictable. In case of unexpected hypoglycaemia, owners should also take glucose syrup with them to give to the dog if necessary, as advised by the veterinary surgeon. Clinical signs to be aware of in such cases include: extreme lethargy; muscle twitches; trembling; incoordination; unusual behaviour and unconsciousness.
Insulin therapy
In most cases, diabetic dogs will have an absolute insulin deficiency (Davison, 2018) and will therefore require insulin therapy. In the UK, Caninsulin (MSD Animal Health) is the only licensed porcine lente insulin preparation available for dogs. Caninsulin is licensed for once-daily use; however for optimal results it is recommended to administer Caninsulin twice daily, beginning with a dose in the region of 0.5 iu/kg. Over the past few years, other insulin products have been explored and this is partly due to the availability of new insulin analogs for human use, and partly due to intermittent availability of porcine lente insulin (Thompson et al, 2015):
- ProZinc (Boehringer Ingelheim) is a long-acting, protamine zinc insulin (PZI) that is registered for use in cats in the USA; however can also be used to manage diabetes in dogs (Maggiore et al, 2012)
- NPH is a recombinant human insulin made by non-pathogenic bacteria, with two brand strains available for use that are biosimilar; however the duration of activity is too short for twice-daily dosing in some dogs (Thompson et al. 2015)
- Detemir is a long-acting, recombinant insulin analog, with a prolonged duration of action due to its binding and slow release from albumin. This product appears to be a promising option for use in dogs in which the duration of action of porcine lente insulin is too short; however close monitoring is required to avoid episodes of hypoglycaemia (Thompson et al, 2015).
Large, controlled studies evaluating the efficacy of various types of insulin products in treating diabetes in dogs have not been published (Thompson et al, 2015).
The decision as to whether insulin therapy is initially done at the owner's home or at the veterinary practice will depend on a number of factors. The first dose should always be given under close supervision with monitoring of blood glucose every 1 to 2 hours for 12 hours. This is to ensure that it does not cause hypoglycaemia. Thus, it is preferable to give the first injection at the veterinary practice. It will take approximately 4–8 weeks to establish the ‘ideal insulin dose’ in each dog and, during this time, the owner will need to be made aware of all the challenges associated with caring for a dog with diabetes, and the dog will need time to equilibrate (usually 3 to 5 days) to the insulin given (Schoeman, 2011). It is preferable that insulin injection times are similar each day, but need not necessarily be at the exact same time as there is considerable day-to-day glycaemic variability of dogs.
A 1 to 2-hourly blood glucose curve will need to be performed in order to adjust the insulin dose and clinical signs should continue to be monitored e.g. ongoing weight loss. This is normally done in the veterinary practice; however some owners can be taught to do this at home as stress may make readings difficult to interpret in nervous dogs. Maintenance of blood glucose monitors is important and their calibration needs to be regularly checked (Ackerman et al, 2018).
Urine testing can be useful and should be checked by owners twice a week as changes in pH or presence of blood or ketones may indicate urinary tract infections or ketosis. Glucose might be detected in the urine; urine glucose correlates poorly with blood glucose and therefore the insulin dose should not be changed based on urine glucose alone (Ackerman et al, 2016).
Owners will need to know how to store insulin correctly as incorrect storage and handling may affect the efficacy of the insulin. Owners can at first find giving insulin injections daunting. However, with support and guidance from the veterinary team (in particular the veterinary nurse) the process can become routine. It is essential to use the correct method of insulin injection and traditionally insulin injections have been given sub cutaneously using a needle and syringe. VetPen (MSD Animal Health, 2014) has been developed to help owners as the device makes giving insulin injections simpler, more accurate and less time consuming. The insulin pens are similar to those used in human medicine. Whatever, the method used, training in the correct technique is necessary. Support information for owners can be found on the MSD Animal Health website. Information includes the use of video footage, which can be beneficial to owners, rather than relying on hand outs.
Conclusion
To conclude, diabetes mellitus in dogs is a common medical disorder affecting approximately one in 300 dogs. The aetiology and pathogenesis of the disease is complex and involves both genetic and environmental factors. Once diagnosed, dogs will require treatment with insulin therapy, regular monitoring and adjustments made to both exercise and diet. Treatment will require a long-term commitment from the owner, but with support it is possible for dogs with diabetes and their owners to achieve a good quality of life.
KEY POINTS
- Hyperglycaemia refers to abnormally high levels of glucose (a simple carbohydrate sugar) in the blood.
- Canine diabetes mellitus is a complex endocrinopathy, with a pathogenesis that varies amongst individuals.
- The aetiology and pathogenesis of the disease remains poorly understood.
- It is important that owners are aware of the strict routine that dogs will need in order to manage the disease.
- The aim of treatment is to minimise hyperglycaemia and its effects.
- Quality of life of both the dog and the owner must be a key consideration.