THE HARD TO REGULATE CAT
The goal in long-term management of diabetes mellitus is the alleviation of unpleasant clinical signs (constant thirst, weight loss, etc.) and prevention of dangerous secondary conditions (infections, ketoacidosis, etc.). To accomplish this, blood sugar levels should be regulated between 250 mg/dl and 80 mg/dl. This is not as good as the body’s natural regulation, but it is a fair and achievable goal in most cases.
Some patients just seem completely unaffected by even high doses of insulin, and it is important to have a step-by-step plan to rule out causes of insulin resistance so that regulation can be achieved.
Insulin resistance is defined as requiring more than
All sugar levels for the day >300 gm/dl despite 6 - 8 units per dose of insulin.
STEP ONE: RULE OUT INSULIN ADMINISTRATION RELATED FACTORS
To review insulin storage and handling click here.
Also important is making sure the diet is appropriate. Soft-moist foods are often preserved with sugars. Extra treats may be interfering with regulation. Remember, ideally a low carbohydrate diet should be fed.
STEP TWO: DETERMINE FOR SURE THAT THE PATIENT IS INSULIN RESISTANT
A glucose curve is needed to distinguish the following three phenomena:
In the case of Somogyi Overswing, the insulin dose is too high and drives the blood sugar low for part of the day. When the blood sugar is low, other hormones such as cortisone or adrenalin are released to raise blood sugar. These hormones can have a prolonged effect (many hours) thus creating hyperglycemia (high blood sugar). If the patient’s high blood sugar has been caused by a Somogyi overswing, a lower dose should be used and a new curve performed in a week or two.
Rapid Insulin Metabolism
In this case, the insulin simply isn’t lasting long enough to create sustained normal blood sugar levels. If the curve shows that the insulin effect is wearing off too soon, twice a day administration of the insulin may solve this problem or a longer acting insulin may be needed.
True Insulin Resistance
Here no significant drop in blood sugar level (levels stay greater than 300 mg/dl) is seen in response to the insulin dose used. Usually there is a history of prior increases in insulin dose all met with minimal response.
We shall continue assuming that the patient has truly insulin resistance on the glucose curve.
STEP THREE: ARE THERE MEDICATIONS BEING USED THAT COULD ELEVATE BLOOD SUGARS?
The obvious medication would be a member of the cortisone (corticosteroid) family. This might be a pill, a shot, an asthma inhaler, or even a topical ointment, spray or ear cleaner. Always keep your veterinarian informed about products you are using.
Progestins (female hormones) were previously used frequently for behavior problems as well as skin diseases in cats. These medications were famous for inducing and promoting diabetes mellitus. If the cat is licking a hormone-containing topical medication from the owner’s skin, this is also important to report.
STEP FOUR: RULE OUT INFECTION
Diabetic animals are at special risk for developing bladder infections since they have so much sugar in their urine. Stress of any kind will contribute to high blood sugar and infection would lead to stress. A urine culture should be done to rule out bladder infection plus the teeth and skin should be inspected for infection in these areas. If infection per se is not found, the patient should be screened for other chronic illnesses that might constitute a stress. A basic blood panel would be a logical starting point.
If infection, or other stress is allowed to go unchecked, ketoacidosis, an especially life-threatening complication of diabetes mellitus can develop.
Do not allow the pet’s teeth to become a source of infection; have teeth cleaning done annually.
STEP FIVE: CONTROL OBESITY
Insulin response is typically blunted in obese patients. If obesity is an issue, it should be addressed. A formal weight loss program using measured amounts of a prescription diet and regular weigh-ins is necessary for success. For general information about weight loss for pets visit:
If these steps do not reveal a relatively simple explanation for the poor insulin response,
HYPERADRENOCORTICISM (“CUSHING’S DISEASE”)
This condition is relatively common in the dog but less so in the cat. In short, this condition involves an excess in “cortisone”-type hormones either from over-production within the body or over-treatment with medication. Cortisone (more accurately referred to as “cortisol”) is secreted naturally in response to a fight or flight situation and prepares the body for exercise by mobilizing sugar stores. If sugar is mobilized into the blood stream in the absence of a fight or flight situation, diabetes mellitus can result. If the excess cortisone situation is resolved, it is possible that the diabetes will also resolve.
About 10% of dogs with Cushing’s disease are also diabetic. About 80% of cats with Cushing’s disease are also diabetic. Testing for Cushing’s disease cannot proceed until some degree of diabetic control has been achieved and the patient is not ketoacidotic.
For more information on Cushing’s disease and its treatment please visit our Cushing’s Disease Information Center.
HYPERTHYROIDISM (CATS ONLY)
Thyroid hormone is another hormone that alters glucose metabolism. While hyperthyroidism is a common condition of older cats, less than 1% of hyperthyroid cats are also diabetic. Still, when a diabetic cat becomes hyperthyroid, control of the thyroid disease generally leads to better regulation of the diabetes.
Acromegaly results from an over-secretion of the pituitary hormone known as “growth hormone.” This hormone normally is responsible for one’s growth from infancy to adulthood. When adulthood is achieved, its secretion dramatically slows, bone growth plates close, and growth essentially stops. If for some reason, this hormone begins secreting again, growth resumes but not generally in normal proportions as the limb bones have closed their growth areas.
One of the effects of growth hormone is causing the body tissues to become resistant to insulin by interfering with tissue insulin receptors. Animals with acromegaly are frequently diabetic.
The prognosis and treatment for acromegaly is very different between dogs and cats. Dogs generally develop acromegaly due to excess progesterone secretion (as would occur from an ovarian cyst). Canine patients are thus usually older unspayed females and spaying may be curative depending on the remaining ability of the pancreas to secrete insulin.
The feline situation more closely approximates the human situation. Cats (and people) develop acromegaly when they develop a growth hormone secreting pituitary tumor. Over 90% of acromegalic cats are male (though there is no sex predisposition in humans.)
The diagnosis of acromegaly can be very difficult. Growth hormone can make soft tissue organs enlarge and cause characteristic proliferation of gum tissue in the mouth but pituitary tumors require some kind of brain imaging (CT scan or MRI) for detection. In terms of blood testing, two values are helpful: a growth hormone level and an “insulin growth factor-1” level. Growth hormone, unfortunately, is not secreted evenly throughout the day meaning there is overlap between what normal cats do and what acromegalic cats do.
Insulin Growth Factor-1, known as “IGF-1” and previously known as “somatomedin C,” is produced by the liver in response to growth hormone and is responsible for many of the effects of growth hormone. IGF-1 can also be measured and may be a more helpful parameter since, unlike growth hormone, it is released in a more steady fashion. (Also, very few laboratories run growth hormone levels so often only the IGF-1 value is available for interpretation.)
Treatment of feline acromegaly is very difficult and may involve radiotherapy of the pituitary tumor causing the problem. Unfortunately, this condition seems to be more common than previously had been thought and research is on-going.
ANTIBODIES AGAINST INSULIN
When a patient is treated with insulin from another species, the immune system recognizes the introduction of the foreign protein and generates antibodies. It was because of this phenomenon that most commercial insulin available is genetically engineered human insulin so that the world’s human diabetics no longer need to worry about making insulin antibodies.
But where does this leave dogs and cats? It leaves them making antibodies against human insulin, that’s where.
To become insulin resistant from antibodies, one must lose 70% or more of the insulin injection to antibody binding. This is very unusual but possible and should not be forgotten as a possible cause of insulin resistance. Blood tests to measure insulin antibodies are available in some areas. Insulin can be switched to a species of origin more closely related to the species desired.
IF A CAUSE CANNOT BE FOUND:
If a cause cannot be found or if treatment for that cause is not practical or possible, the good news is that multiple high doses of insulin can generally overcome the resistance. Sometimes combinations of short and long-acting insulins are used together to achieve reasonable regulation. Some of the oral agents listed in the section on Controlling Diabetes Without Insulin may be helpful. It may be necessary to consult an internal medicine specialist.
To find an internal medicine specialist near you, visit:
Page posted: 1/20/10