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This case got me thinking about the reasons (other than behavior) why diabetic cats can become difficult to regulate. These patients end up on unusually high doses of insulin (greater than one unit per pound) but still suffer from the typical symptoms of diabetes mellitus, including:
The first step in figuring out what is going on with a difficult to regulate diabetic is to examine the care the animal receives at home. Is the cat eating an appropriate amount of a low carbohydrate diet? Canned foods are best. Is the owner using good injection technique? Oftentimes it is best to avoid injecting around the nape of the neck and use the flank areas instead. Are appropriate insulin and insulin syringes being used? A mismatch can lead to under or overdosing. Is the insulin handled appropriately (refrigerated, replaced every three months or so)? Are any other medications being given? Some (e.g., corticosteroids) interfere with glucose regulation.
Once home care has been validated, it’s time to look at the cat itself. Concurrent disease is the primary reason why some cats do not respond to “normal” doses of insulin. Infection and inflammation anywhere in the body leads to insulin resistance. Dental disease and undiagnosed urinary tract infections are common culprits. Urinary tract infections in diabetics are common (because the sugar in the urine promotes bacterial growth) and can’t always be diagnosed with a routine urinalysis. A urine culture is often necessary.
The list of other diseases that can cause insulin resistance in cats is long and includes acromegaly, hyperadrenocorticism, concurrent pancreatic disease, hyperthyroidism, kidney disease, liver insufficiency, and heart disease. Some of these conditions are easy to diagnose; others are not. Therefore, working through the entire list can take some time.
Finally, I must mention something called the Somogyi effect, defined as “a higher than normal blood glucose level that occurs after an animal is overdosed with insulin and the body has responded to the resulting hypoglycemia.”1 To rule out the Somogyi effect, every difficult to regulate diabetic cat should undergo a full glucose curve, consisting of blood glucose measurements taken every two hours over a twelve hour period, starting immediately prior to the morning insulin injection and ending just prior to the evening insulin injection. This allows the veterinarian to determine what the high and low measurements for the day are. If at any time the cat’s blood sugar level is significantly below normal, the answer is not more insulin but less.
Dr. Jennifer Coates for PetMD
1. Coates J. Dictionary of Veterinary Terms: Vet-speak Deciphered for the Non-Veterinarian. Alpine Publications. 2007.