Definition of Diabetes
Diabetes is a general term used to refer to a variety of disorders characterized clinically by excessive water intake and urine output. There are two “big” categories of diabetes in cats, dogs and people: diabetes insipidus and diabetes mellitus. Of these, diabetes mellitus is by far the more common in companion animals.
Diabetes insipidus is a metabolic disorder that ultimately results in the inability of the cat’s kidneys to reabsorb water properly, which leads to an abnormally large volume of urine and great thirst. Diabetes mellitus is a widely-used term for a complicated, chronic and incurable disorder of the endocrine system that involves abnormal glucose metabolism. This occurs when certain pancreatic cells cannot produce or release an adequate supply of insulin, or alternatively when a cat’s cells are unable to take up and use the insulin that is produced. Insulin is the chief regulator of the path that dietary sugar takes, but also affects fat and protein metabolism.
How Diabetes Mellitus Affects Cats
Insulin-dependent or Type I diabetes mellitus, which is caused by the destruction (or even absence) of certain cells in the pancreas which normally are responsible for producing insulin, occurs in cats but more commonly occurs in older, obese female dogs. Animals with insulin-dependent diabetes have very low natural blood insulin levels and an abnormally low response to injected glucose. Cats also develop non-insulin-dependent, or Type II, diabetes mellitus, in which the production and secretion of insulin is unimpaired (there is a high or normal blood insulin level), but the response of the cat’s cellular receptors to insulin is abnormal such that the cat’s tissues cannot uptake and metabolize glucose normally. In diabetic cats, the body's tissues cannot properly assimilate and use all of the important components in food (carbohydrates/sugar, fat, protein). By diminishing the cat's ability to turn food into useful fuel for its body, diabetes effectively puts the cat into starvation mode.
Increased thirst, water intake and urination are key signs of a diabetic syndrome. In the early stages of diabetes, cats tend to become less active, lose their appetite, stop their normal grooming and develop a poor hair coat. In more severe cases, the cat will have a voracious appetite yet will still lose weight and have muscle wasting and an oily hair coat accompanied by dandruff. Cats also frequently exhibit decreased jumping ability and hind end weakness. In late stages, diabetes can cause complete loss of appetite, vomiting, lethargy, abdominal pain, lack of coordination, weakness and death. There are some severe but rare complications of untreated diabetes, although the cataracts commonly seen in diabetic dogs and people are not reported in cats.
Causes of Feline Diabetes
Diabetes mellitus affects a cat’s ability to transfer energy from dietary glucose (carbohydrates/sugars) to its cells. Insulin is necessary for this energy transfer. When the cat’s pancreas does not produce and release enough insulin, or if the body’s cellular receptors cannot take up the insulin that is produced and released, there will be an insufficient amount of glucose available for cellular uptake, and the animal will not have the normal amount of energy to survive. The cat’s blood will become saturated with glucose. Diabetes mellitus usually is seen in middle-aged to older and cats, with overweight intact females much more commonly affected than males. An inherited component has been suggested but has not been conclusively established. Other risk factors include obesity, recurring pancreatitis, hyperadrenocorticism and administration of drugs which can antagonize the effects of insulin.
Diabetes mellitus tends to occur more frequently in older cats, more so in neutered males, with no particular breed predilection in the United States. Interestingly, Burmese cats have been reported to be overrepresented in Australia. The prevalence of this disease in cats is approximately 1:200, so it is remarkably common. There is no single known cause of feline diabetes mellitus. Recurrent pancreatitis, inherited susceptibility, environmental factors, hyperadrenocorticism (which causes insulin resistance), obesity and certain medications (glucocorticoids, progestogens) have all been reported to be associated with development of feline diabetes. Amyloid deposits, which interfere with pancreatic function and can exacerbate the progression of diabetic disease, are frequently seen in tissue samples from diabetic cats as well.
Preventing Diabetes in Cats
There is no tried and true way to prevent diabetes in cats. Owners should feed a well-balanced diet and prevent or correct obesity in their cats. Owners should also avoid unnecessary use of steroid medications, which can contribute to this disease. Affected animals probably should not be bred due to a possible genetic component to this disease, which at this time is not well understood.
Early diagnosis is critical in order to effectively treat or at least manage diabetes in cats. Owners should educate themselves about the clinical signs of diabetes – especially polyuria (increased frequency of urination), polydypsia (increased thirst and water intake), polyphasia (increased appetite and eating) and weight loss - and should take their cat to their veterinarian if these signs show up.
Diagnosis of diabetes is made by at first conducting a complete history, physical examination and complete blood count, biochemical profile and urinalysis. Other more advanced and specific diagnostic tests are available to confirm the diagnosis of feline diabetes. Cats can develop high blood sugar during periods of intense stress, so elevated levels should be reevaluated periodically. Blood insulin levels may not help distinguish between Type I and II diabetes mellitus in cats. Glucose tolerance tests are widely used in humans for diagnosis of diabetes, but because of quirks of the feline species are not used as a screening test in cats. There are other blood tests that can measure feline blood sugar trends and are an excellent way to distinguish true diabetes from stress hyperglycemia in cats.
The prognosis for diabetic cats depends upon a number of factors, including the owner’s commitment to following specific treatment protocols. Typically, diabetes is very manageable if owners are diligent about their role in ongoing therapy. Fortunately, with proper care, diabetic cats usually can maintain a good quality of life for many years.