Diabetes pathophysiology and disease management

Diabetes is one of the most common endocrine diseases seen in companion animal veterinary practice, but it can still be quite a challenge to effectively educate clients in the care of their diabetic pet. Veterinary nurses play a large role in the successful management of diabetic patients by carrying out such tasks as collecting diagnostic samples, administering medications, providing skilld nursing care and through advising pet owners. To fulfill these nursing roles, it is important that veterinary nurses have a good foundation of knowledge in the diabetic disease process as well as being well versed in some of the most common treatment and management protocols.

The basics of diabetes pathology

Diabetes is an endocrine disease affecting some of the glands that regulate metabolism. There are two main forms of the disease, diabetes insipidus and diabetes mellitus:

• Diabetes insipidus — This form of the disease, also known as ‘water diabetes’, is relatively uncommon in dogs and is hardly ever seen in cats (Rossi et al, 2008). It results from a lack of, or insensitivity to, vasopressin hormone, which is produced by the pituitary gland in the brain. Vasopressin regulates primary body fluid balance by signalling the kidneys to conserve water; when the hormone is insufficient, or is not recognized by the kidneys, fluid may not be conserved and a dilute urine will be produced, regardless of the body's overall hydration level.
• Diabetes mellitus — This common form of the disease is also known as ‘sugar diabetes’ and presents in many different ways. It has many potential causes. It results from a failure of the body to metabolize glucose as a result of a lack of, or insensitivity to, insulin hormone. Insulin is produced by the pancreas, a digestive gland located near the stomach.

Diabetes mellitus is far more commonly seen in veterinary clinical practice than diabetes insipidus, and, therefore, will be the primary area of focus for this article.

There are a few ways that the disease can present: insulin dependent diabetes mellitus (IDDM); non-insulin dependent diabetes mellitus (NIDDM); and secondary or transient diabetes mellitus.

IDDM

This form of diabetes is related to ‘type I’ diabetes in humans and is more common in dogs, but can be seen in cats. In dogs, as with humans, there is evidence of an immune response leading to antibody destruction of insulin-producing cells in the pancreas. In dogs IDDM is more closely related to body weight than in humans; dogs' excess body weight can sometimes lead to insulin resistance and this can lead to the destruction of insulin-producing cells in the pancreas. This condition causes overproduction of glucose by the liver and under utilization of glucose in the body outside of the liver. There is also a high likelihood of ketone body production, thus ketoacidosis is more common with this form of the disease (Griffin and Ojeda, 2000).

NIDDM

This form of diabetes is related to human ‘Type II’ or ‘insulin-resistant’ diabetes. It is strongly linked to obesity and is more common in cats than in dogs. Extreme hyperglycaemia and subsequent hyperosmolar nonketotic coma may be seen with this form of the disease.

Secondary or transient diabetes mellitus

Unlike IDDM, which is a permanent condition, there are a number of drugs and disease states that can cause temporary NIDDM. Insulin resistance and destruction of insulin producing cells in the pancreas can be caused by a number of drugs and disease states, but if the underlying cause is remedied the pancreas can often recover near normal function (Feldman and Nelson, 2004). Transient diabetes is particularly common in cats. Cats almost always require initial insulin supplementation, however, as many as 30 to 80% of cats no longer require insulin after implementation of successful lifestyle and dietary modifications (Sessions et al, 2008).

Causes

There are many contributing factors to the development of diabetes in dogs and cats. There is a genetic predisposition to IDDM and a strong correlation between obesity and NIDDM (American Animal Hospital Association, 2010). As mentioned above, dogs are more prone to IDDM and cats are more prone to NIDDM, however, cats can progress from NIDDM to IDDM (Harari and Luce, 2007). The gender of the animal can also play a role, where female dogs and male cats are more likely to contract the disease (Feldman and Nelson, 2004). The incidence of cats acquiring the disease as juveniles is uncommon with the majority presenting after the age of 9 years (Harari and Luce, 2007). Other contributing factors for the disease include concurrent or chronic conditions such as pancreatitis, hyperthyroidism, hyperadrenocorticism, infection, ketoacidosis and drug toxicity.

Clinical signs

Classically, all forms of diabetes almost always present with polyuria and polydipsia. There are a number of other signs that may also be seen with diabetes mellitus including polyphagia, and weight loss (Table 1). It is important to note that clinical signs of diabetes are usually not present until the blood glucose reaches the renal threshold (the point at which the concentration of glucose rises such that the kidneys begin to excrete it) and glucose begins to be excreted in the urine (Rios and Ward, 2008). Animals with diabetic ketoacidosis may present with signs such as anorexia, depression, abdominal pain, vomiting, diarrhoea and dehydration.

Diagnostics

Blood glucose measurements are important for accurate diagnosis and ongoing monitoring of diabetes. Diabetes mellitus is diagnosed by a persistent blood glucose level >0.11 mmol/L (>200 mg/dL) in the dog and >0.14 mmol/L (>250 mg/dL) in the cat (Rucinsky et al, 2010). The levels of blood glucose can fluctuate, particularly in cats that are stressed, so it is important to be assured that the hyperglycaemia is persistent and present even when the animal is fasting. Elevated serum fructosamine levels can confirm the diagnosis of diabetes in cats, when transient hyperglycaemia is suspected. Glucose may be seen in the urine once blood levels have reached approximately 0.10 mmol/L (180 mg/dL) in dogs and ~0.13 mmol/L (~DC;240 mg/dL) in cats (Merck, 2008). It is also beneficial to evaluate the animal for a number of other conditions that can cause or result from diabetes since these may present as complicating factors to patient management. These include urinary infection, concurrent endocrine disease, chronic pancreatitis, inflammation or infection (Geyer et al, 2007).

Treatments

The primary goal of treatment for dogs and cats with clinical diabetes is to prevent the appearance of clinical signs and avoid disease complications such as neuropathy and ketoacidosis. It is also important to ensure the client feels satisfied with the treatment and is happy that their pet is achieving a good quality of life (Rucinsky et al, 2010).

Treatment of diabetes mellitus in cats and dogs almost always includes some sort of insulin supplementation (Figure 1) and ongoing blood glucose monitoring (Figure 2). This can be a daunting proposition for clients who may be uneasy about handling needles or unfamiliar looking pen devices, and who might be unaware of how to monitor their pet's wellbeing. Good client communication and support are essential for the effective management of the diabetic patient.

When the animal is initially diagnosed with diabetes mellitus the veterinarian will determine the dosage of insulin that needs to be administered each day, and the client will be educated on procedures for using the insulin pen device or using a syringe and needle to draw up and administer insulin to their pet. There are many risks involved with administering insulin so it is essential that the client is comfortable with the techniques involved as well as fully aware of the consequences of incorrect administration. Underdosing insulin can result in hyperglycaemia and this may cause the return of clinical signs of diabetes. Overdosing insulin can cause acute hypoglycaemia and can quickly progress to death if not corrected promptly (Table 2). It is also vital that the client is aware of the correlation between feeding and the need for insulin to help ensure that insulin is only given if the animal is eating normally. They should be prepared to act immediately on signs of insulin overdose (such as weakness, ataxia, seizure and coma), contacting the veterinary practice straight away and offering oral glucose if needed (Miller, 1995).

Weight loss can be beneficial for patients with NIDDM by reducing the insulin requirements and in the case of cats, weight loss and a restricted carbohydrate diet can even eliminate the necessity for prolonged insulin supplementation in some cases (Laflamme, 2010). When feeding a low carbohydrate diet to cats, the protein requirement must be higher (>45% protein metabolizable energy) to ensure that the cat maintains good metabolism and body condition (American Animal Hospital Association, 2010). New drug therapies may also provide better disease control to patients with poorly controlled NIDDM. Incretin-based therapy is one such advance that is already being used in humans by utilizing drugs that mimic glucose normalizing digestive hormones. These drugs are currently being trialed in animals and it may only be a matter of time before they become common in veterinary practice.

Natural variations in the pet's diet, exercise, and stress levels can alter its daily insulin requirements and this can result in unexpected results when administering a set insulin dosage at home. In many cases the long-term implications are minimal, but it is nonetheless important that the client is well versed in signs of hypo and hyperglycaemia (Table 2) and what action to take if these conditions are detected. As with humans with diabetes, daily blood glucose monitoring is beneficial in terms of assessing the daily insulin needs, and it is becoming increasingly common for clients to learn how carry out blood glucose monitoring in their home (Figure 3). There are numerous online sources that detail a number of different methods for home monitoring and veterinary nurses play an important role in assisting the client to implement a method that works well for their pet and lifestyle. Even if the pet's blood glucose is checked no more than once per day, home monitoring has the advantage of allowing immediate feedback to the clinic about the animal's glucose levels. The veterinary surgeon can outline which results are within a normal range for the pet and at what point the client should contact the veterinary practice for evaluation of an abnormal result. This type of continual care can improve overall patient management and enhance client satisfaction (Tucker and Wortinger, 2005).

Every 3 to 6 months the veterinarian may wish to evaluate the effectiveness of the insulin dose and this is typically done with a glucose curve that may be conducted at home by the client, or while the animal is hospitalized in clinic. The animal's response to the normal insulin dose, as determined by several blood glucose tests throughout the day, will determine how effective the insulin dose rate is at establishing acceptable blood sugar levels. Results may indicate that the dose rate needs to be adjusted to maintain effectiveness and safety for the patient (Fleeman and Rand, 2003).

Nursing considerations

In terms of critical care, diabetes can present with acute illness. Diabetic ketoacidosis is a common complication of IDDM and in the advanced stages can present with a number of clinical signs (Table 3). Along with insulin supplementation, fluid and electrolyte imbalance must be corrected. Careful monitoring of mental status, hydration, urine output and blood glucose are essential to ensure that the patient is not suffering from wide swings in blood glucose from the action of the insulin. The patient can be fed to prevent an excessive drop in blood glucose and if the patient is not eating then supplementation with intravenous dextrose may be prescribed by the veterinarian (Battaglia, 2001). As with all critical care patients, good supportive care can provide comfort for the patient and the client until such time as the patient is stabilized.

Veterinary nurses also play an important role in detecting signs of diabetes during nursing clinics or by talking to clients on the phone. Clients can be made aware of the importance of bringing their pet in for a thorough evaluation by the veterinarian, and if diabetes is diagnosed, the veterinary nurse can help educate the client about the treatment plan. There are a number of very good resources online (see Good client education sites) for educating clients about caring for diabetic pets, and these can be useful for the practice as supportive materials when sending diabetic animals home.

Once a diabetic animal goes home with a treatment plan, client compliance is essential for successful disease management. The veterinary nurse plays a vital role in facilitating this working relationship by providing knowledgeable advice and ongoing support. Adherence to dietary plans and dosing schedules is key so feeding times may need to be adjusted to suit the client's schedule and ensure regular administration of insulin as well as observation of the animal for a time after medicating. Feeding and dosing logs can be very helpful for the ongoing monitoring of the effectiveness of the treatment plan. These logs can be regularly reviewed by the veterinary nurse during clinic visits or by telephone follow up.

Conclusion

Diabetes is a complicated disease that has many different manifestations, but in general diabetes mellitus is the most common form of the disease seen in companion animals. Cats will usually present differently in terms of clinical signs and response to drug therapy compared with dogs, but there are a number of successful treatment strategies that can enable the diabetic dog or cat to lead a long fulfilling life. Client compliance is vital for the successful management of diabetic pets at home so the client must be educated on the treatment objectives for their pet and how to easily recognize changes in their pet's behaviour, appetite or activity level, which might indicate that the disease is not being controlled effectively. Regular checkups and good communication between the client and the clinic can help detect problems and ensure that the treatment plan is being implemented effectively. Good support by the veterinary nurse can significantly improve the client's outlook and thus promote good ongoing management of the patient's disease progression. By working together, the client and the veterinary staff can ensure a suitable treatment plan is carried out effectively and this will help ensure that the patient is able to live with minimal impact from the disease.

Suggested readingAAHA Diabetes Management Guidelines for Dogs and Catshttp://www.aahanet.org/resources/DiabetesMgtGuidelines.aspxVIN Client Information Sheet: Home Testing of Blood Glucose for Diabetic Catshttp://www.veterinarypartner.com/Content.plx?P=A&A=605Good client education siteswww.felinediabetes.comwww.caninediabetes.orghttp://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=631

To answer the CPD questions on this article visit www.theveterinarynurse.com Questions have been approved by Harper Adams University College

Key Points

• There are many different forms and presentations of diabetes in dogs and cats.
• Dogs and cats are likely to have different forms of diabetes mellitus.
• Clinical signs of all types of diabetes can include polydipsia and polyuria.
• Treatment for diabetes mellitus varies for dogs and cats.
• Management of diabetes mellitus is aided by veterinary nurses who are familiar with the disease pathophysiology.