Diabetes mellitus (DM) in dogs and cats has many causes, just as there are multiple causes in people.
Canine diabetes mellitus is always Type 1, or insulin-dependent diabetes mellitus (IDDM). Type 1 diabetes results from congenital or acquired failure to produce insulin, requiring insulin replacement therapy by injection.
On the other hand, cats may be afflicted by Type 1 or Type 2 diabetes. Type 2 diabetes is defined as high blood glucose caused by resistance to insulin, a defect in the insulin receptor of cells. Type 2 DM can, however, be accompanied by an absolute lack of or reduced levels of insulin.
Insulin is a hormone produced by β- (beta) cells in the Islets of Langerhans in the pancreas. Insulin is required for the mammalian body to utilize glucose (sugar) for energy in cells all over the body. In the absence of insulin, glucose accumulates in the bloodstream (hyperglycemia) and many body functions fail. Long-term lack of insulin eventually results in death.
Inheritance is almost certainly a factor for dogs developing diabetes, but little research has been performed in this area for cats. It is known that heritability of diabetes in humans involves multiple genes. Breed predisposition exists only Burmese cats, which lends additional evidence for genetics as a possible cause.
An immune-mediated (autoimmune) cause of diabetes in pets has been researched, but scientists have not yet been able to identify specific causal factors.
Endogenous and exogenous corticosteroids can result in DM, presumably by causing exhaustion of the beta cells’ ability to produce insulin as well as contributing to insulin resistance. The presence of elevated levels of glucocorticoids causes increased glucose production in the liver, gluconeogenesis, raising blood glucose levels. That increase in blood sugar results in increased production of insulin which, over time, can permanently exhaust the β-cells’ function. Endogenous cortisol most commonly results from pituitary-dependent or adrenal Cushing’s Disease. Exogenous corticosteroids are administered by the veterinarian and/or pet owner for a variety of medical conditions.
An exogenous steroid unique to cats is the therapeutic use of megestrol acetate. There are a number of dermatologic conditions in cats which respond to megestrol, and, while it can be used safely on a limited basis, long-term usage almost always leads to diabetes development. Feline diabetes from megestrol acetate use is caused by its glucocorticoid properties, even though it is the progestin family, similar to naturally-produced progesterone.
Diabetic cats with dermatologic complaints must have their conditions managed by non-steroidal means.
Pancreatitis is inflammation of the pancreas. Because beta cells reside in the pancreas, and nowhere else in the body, they may be damaged during inflammatory episodes. Should the pancreatitisbe widespread, and enough islets are destroyed, insulin production may fall below a level commensurate with good glucose control, and diabetes mellitus results.
Not so long ago practitioners felt pancreatitis in cats was at least unusual, if not rare. The advent of the fPLI (Feline Pancreatic Lipase Immunoreactivity) reference laboratory test and its more-recent cousin, the Spec fPL® (Feline Pancreas-Specific Lipase) in-clinic test has proven that many more cats have inflamed pancreases than was previously believed.
Acromegaly (hypersomatotropism) is a condition caused by excessive production of growth hormone by the pituitary gland. Growth hormone (GH) production should decrease around the time of physical maturity, but acromegalic individuals experience continued bone growth. The word derives from the Greek akron, meaning “extremity” and megas meaning “large.” Because growth plates of bones close at their usual time, long bones may become thickened and bowed. Bones of the skull and jaw become prominent and misshapen. An abnormally-large head may result. The vast majority of affected cats are male. Like other steroid hormones, growth hormone also has the ability to interfere with insulin receptors, leading to insulin resistance. Diagnosis and treatment of feline diabetes may begin as with a typical diabetic cat, yet the cat’s diabetes is difficult or impossible to manage.
See you tomorrow, Dr. Randolph.