Diabetes mellitus is an absolute or relative deficiency of the hormone insulin. Insulin is synthesized and released from beta cells in the pancreatic islets. Insulin assists with cellular uptake of glucose from the bloodstream into the cells of the body for energy. This causes a hypoglycemic effect. Within cells, insulin promotes anabolism, such as the production of glycogen, fatty acids, and proteins, and counters catabolic events to reduce gluconeogenesis and inhibit fat and glycogen breakdown.
Insulin lowers blood glucose, whereas opposing hormones including glucagon, cortisol, progesterone, adrenaline, thyroid hormone, and growth hormone increase blood glucose. It’s important to consider these counterregulatory hormones, because changes in their blood concentrations interfere with insulin actions. Changes in these hormones result from natural physiological conditions, disease states, or drug administration.
As the blood glucose concentration increases due to insufficient insulin, the kidneys become overwhelmed by the blood glucose concentration and glucose spills into the urine. The osmotic action of glucose leads to polyuria and, through loss of fluid, to polydipsia.
In the absence of sufficient insulin, cats with diabetes will switch from glucose to fat metabolism for cellular energy. While this is initially beneficial, fat metabolism in unrecognized or untreated cats typically causes a deteriorated general condition and progresses to ketoacidosis and ultimately to death.
Diabetes mellitus is not related to diabetes insipidus, an extremely rare condition in cats that occurs when the kidneys are unable to regulate fluids in the body. Diabetes insipidus is characterized by a deficiency or inadequate response to a hormone called vasopressin.
Prevalence of diabetes mellitus in cats is estimated at 68 cats per 10,000 cases.1 Diabetes occurs more commonly in cats that are considered obese. Diabetes is also more common in middle- to older-aged cats. Neutered male cats are at greater risk than female cats.
1 Banfield State of Pet Health 2016 Report. p 12-13.
Determining an effective treatment regimen for cats with diabetes can be challenging. Factors that affect the type and success of treatment include:
- The severity of pancreatic beta cell loss
- The responsiveness of tissues to insulin
- The presence or absence of glucose toxicity
- Problems with absorption and duration of effect of exogenously administered insulin
- Presence of concurrent disease
Most forms of diabetes can be successfully treated with medications, but dietary adjustments and a regular lifestyle are also important. For many years, insulin has been the cornerstone of successful management of diabetes mellitus in pets.
In general, the prognosis for cats with diabetes is very good, especially with early diagnosis and proper therapy. Additional factors that affect the prognosis for cats include:
- Owner commitment to disease management
- Presence and nature of concurrent disorders (e.g., pancreatitis, acromegaly)
- Avoidance of chronic complications
The most common chronic complication of diabetes in cats is the development of peripheral neuropathy, which is exhibited by weakness in the hind legs. Diligent control of hyperglycemia can potentially reverse the clinical signs of neuropathy, but it can take several months. Also, recurrent infections commonly affect both dogs and cats with diabetes.
Open communication between you and your client is an extremely important factor. Encouraging your clients helps ensure their motivation and compliance with management. Clients need to fully understand the disease to help achieve and maintain good diabetic stability and be highly motivated and committed to the management of their cats. Your clinical staff also has an important role in providing detailed client education, instruction, and encouragement.
Several classification systems have been used to describe diabetes mellitus. A human classification system revised in 1997 divides the disease into three types: Type 1 (previously insulin-dependent or juvenile-onset diabetes mellitus), Type 2 (previously non–insulin-dependent or adult-onset diabetes mellitus), and other specific types of diabetes mellitus (previously secondary or Type 3 diabetes mellitus).
Diabetes in cats more closely resembles Type 2 diabetes in people in that it is believed to be associated with a relative rather than absolute deficiency in insulin. Like people with Type 2 diabetes, dietary manipulation plays an important role in the management of diabetes in cats. Cats differ in that most will need additional treatment, like exogenous insulin, in order to maintain adequate regulation.
Although diabetes in cats is similar to Type 2 diabetes, chronic hyperglycemia will typically lead to glucose toxicity, which will lead to loss of pancreatic function, resulting in insulin requirement. With proper treatment, including dietary manipulation and other therapies, pancreatic function can return and remission can be achieved.
Glucose toxicity occurs when insulin secretion is reduced due to prolonged hyperglycemia. Prolonged hyperglycemia and diabetes mellitus can occur following prolonged and high-dose therapeutic use of glucocorticosteroids or exogenous progestogens. Progestogens have an antagonist effect on insulin, as they can lead to growth hormone excess and also have an affinity for glucocorticosteroid receptors.
Hypoglycemia occurs when the blood glucose level drops to 3.3 mmol/L (60 mg/dL) or less. Hypoglycemia may be triggered by:
- Insulin dose too high
- Overlapping insulin dosage
- Loss of appetite
- Vomiting
- Excessive exercise
The clinical signs of hypoglycemia that cat owners should be able to recognize are (in order of severity):
- Hunger
- Restlessness
- Shivering
- Incoordination
- Disorientation
- Convulsions and seizures
- Coma
It’s important to alert your cat-owning clients that early signs of hypoglycemia may be subtle. Also, some cats will simply become very quiet and inappetent.
Coach your clients to watch for abnormal behaviours associated with hypoglycemia, and to contact you if they are concerned it is present.
Immediate oral administration of glucose solution or corn syrup (1 g per kg body weight). An alert animal may be fed a small amount of food. Animals that are collapsed should not have large volumes of fluid forced into their mouths as this may result in aspiration pneumonia: here it is preferable to rub a small amount of the glucose solution or corn syrup onto the animal’s gums or under its tongue.
- Intravenous dextrose solution can be administered to effect in severe cases or if oral therapy has been ineffective.
- Owners of pets with diabetes should always have a source of glucose readily available. Following the successful emergency administration of oral glucose, small amounts of food should be offered at intervals of 1–2 hours until the effects of the insulin overdose have been counteracted. Blood glucose monitoring should continue through entire duration of action of insulin (i.e. 12 hours for twice daily insulin and 24 hours for once daily insulin).
- If the insulin dose is too high, reduce it by at least 10-50% and reassess.
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