Diabetes mellitus, or sugar diabetes, is a commonly diagnosed disease in cats and ultimately affects all the organs. It develops in about 1 in 400 cats. It is due to inadequate production of insulin by the beta cells in the pancreas or inadequate response of the cells to insulin. Insulin is secreted directly into the circulation. It acts upon cell membranes, enabling glucose to enter the cells, where it is metabolized for energy. Without insulin, the body can’t utilize glucose. This results in elevated blood sugar levels (hyperglycemia). In diabetic cats, excess glucose is eliminated by the kidneys, producing frequent urination. There is a need to compensate for the increased urination by drinking unusual amounts of water.
Pancreatitis, hyperthyroidism, medications such as megestrol acetate (Megace), and some corticosteroids, all have the potential to cause or mimic diabetes in a cat. Obesity is a predisposing factor for all cats, and Burmese cats may have a genetic predisposition. Male cats have twice the risk of females. At greatest risk are neutered male cats over 10 years of age and over 15 pounds in weight.
Glycosuria is sugar in the urine. When a urine glucose test is positive, suspect diabetes. Some cats will show high glucose levels in urine and blood due to stress, however, so a repeat test may be needed to verify the results. Defects in the kidney tubule function, such as with antifreeze poisoning, may also cause high glucose levels in the blood and urine.
Ketones (the end-product of rapid or excessive fatty-acid breakdown) are formed in the blood of diabetics because of the inability to metabolize glucose. High levels lead to a condition called ketoacidosis. It is characterized by acetone on the breath (a sweet odor like nail polish remover); rapid, labored breathing; and, eventually, diabetic coma.
In the early stages of diabetes, a cat will try to compensate for the inability to metabolize blood glucose by eating more food. Later, with the effects of malnourishment, there is a drop in appetite. Accordingly, the signs of early diabetes are frequent urination, drinking lots of water, a large appetite, and unexplained weight loss. The laboratory findings are glucose and possibly ketones in the urine and a high blood glucose level.
In more advanced cases, there is loss of appetite, vomiting, weakness, acetone breath, dehydration, labored breathing, lethargy, and, finally, coma. Unlike dogs, diabetic cats rarely develop cataracts. A muscle weakness, usually shown by an unusual stance in the rear with the cat walking down on her hocks instead of up on her toes, is often seen if glucose regulation is poor.
Three types of diabetes are seen in cats. Type I diabetic cats are insulin dependent and need to receive daily insulin injections because the beta cells of their pancreases are not making enough insulin. In cats with type II diabetes, the cat’s pancreas may make enough insulin but the cat’s body does not use it properly. This is the most common type of feline diabetes. Some of these cats will require insulin as well, but others may get by on oral drugs to control blood glucose and dietary changes. About 70 percent of all diabetic cats will require at least some insulin.
The third type is known as transient diabetes. These are type II cats who present as diabetics and require insulin initially, but over time, their system re-regulates so they can go off insulin-especially with a change to a high-protein, low-carbohydrate diet.