My 14 year-old domestic short-haired cat, Isaac, has been diabetic for a little over a year. He was well-controlled, and even went into diabetic remission, meaning that he was completely off insulin for a few months (cured, essentially).
Then he started drinking and urinating more, a clear sign that his glucose (sugar) was high. Chronic stress could lead to insulin resistance, however, this cat is virtually never stressed. He's the coolest cat I've ever met (no bias there). A herd of wildebeest can run through the house and he would not bat an eye. Three dogs were recently brought over to the house while family was here for dinner. Isaac lazily plopped himself in the middle of the living room while three dogs goaded him in vain to initiate a game of dog-chase-cat. No such luck.
While his insulin requirements crept up with no drop in his blood glucose, I became strongly suspicious of an underlying problem. Possibilities include an infection (anywhere in the body), a tumor, or another endocrine (glandular) problem, like Cushing's for example, and other issues.
Extensive testing, including an abdominal ultrasound and chest x-rays revealed nothing - not an iota of an inkling of a suspicion of a problem, including Cushing's.
He started to become even more pot-bellied and when he would hitherto eat nothing but the right cat food, Isaac started asking us for table food: pizza, (the occasional) McDonald's hamburger, risotto, filet mignon, chicken breast, deli turkey slices, yams, fries, and the list goes on.
This prompted me to suspect a disease (some say close to a third of diabetic cats are affected) called acromegaly, also known as gigantism. Test results came in today and Isaac's numbers were unequivocally consistent with the disease. This explains the consistently high blood glucose. Besides the high sugar, I am relieved that he is clinically well and he could stay this way for months to years.
Here, the vet has diagnosed acromegaly for the first time - in his own cat.
The same woman, young and normal in appearance on the left; older with signs of acromegaly in the middle and on the right (pronounced chin and underbite, enlarged head, and severely thickened fingers, etc.).