The Case of the Not-So-Resistant Diabetic Kitty
1. Referral:
“Kitty” is a nine year old DSH who presented for a second opinion on insulin-resistant diabetes. “Kitty” is a 5 kg cat who was diagnosed with diabetes mellitus 6 months ago. She was started on 3 units of NPH q 12hours. The cat had repeated rechecks with her RDVM who would check a blood glucose approximately 6 hours after insulin was given. These values were consistently greater than 350mg/dl. With each visit, the elevated BG was interpreted as meaning the cat needed more insulin and her insulin was increased. In addition, she continued to have signs consistent with unregulated diabetes. She was still PU/PD, polyphagic, and was losing weight. On presentation to me, she was on 7 units of NPH insulin q 12hours.
2. Exam:
On physical exam, Kitty was BAR and purring. She weighed 4 kg and had a body condition score of 3.5/9. No other significant findings were noted on physical exam.
3. Procedures:
During the exam, I discussed insulin resistance with the owner. Kitty is not at a level of insulin that is absolutely diagnostic for insulin resistance (> 2units/kg) but she is way above a dose which should regulate her. We discussed that the next step was full bloodwork to rule out other underlying diseases and a glucose curve to rule out a somogyi effect.
“Kitty’s” owners were instructed to drop her off the next morning for a glucose curve. The owners were instructed to follow her normal morning routine by feeding and giving her insulin dose and then to bring her immediately in. A blood glucose reading was obtained immediately upon arrival and then every 1-2 hours afterwards.
4. Diagnosis:
• Insulin overdose (somogyi effect)
• Short duration of action of insulin
5. Discussion:
This case is a fantastic example of how helpful glucose curves can be in the management of diabetic animals. This curve highlights an animal who has a very short onset of action of NPH insulin. The peak onset of action in “Kitty” was 4 hours. Her previous monitoring was done via spot checks of blood glucose levels at 6 hours post insulin (which should have been around her peak action if her duration of action was in fact 12 hours). In “Kitty”, by 6 hours, her blood glucose is already on its way up. This value is >350 mg/dL. If this value is looked at on its own, it is easy to misinterpret that this cat needs more insulin and increase her dose. This is especially true given her persistence of clinical signs. By increasing her dose, we have set up a Somogyi effect where her blood glucose plummets and then rises dramatically all within 12 hours.
By looking at “Kitty’s” curve, you can see that she spends the majority of her day hyperglycemic which explains her persistent clinical signs. Only by curving her can you identify that she does not need more insulin but instead needs a change in insulin and now a decrease in dose.
6. Recovery:
“Kitty” was changed to 1 unit of glargine (Lantus) insulin q 12 hours. Repeat curves revealed that this dose was appropriate. “Kitty’s” signs resolved and she began to maintain her weight.
by Emilie Chaplow, VMD,
Diplomate American College of Veterinary Internal Medicine
*Photo of Cat is not “Kitty.”