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Pyelonephritis: a kidney infection. Literally, pus in the kidneys (see a very early post of mine). I treated two such cases in the last two weeks. These were very sick cats, clinically affected with laboratory values consistent with pyelo (that's what we call if for short). Often, these cats don't read the textbook, but both of these did. Both were painful on kidney palpation, their total white blood cell counts were significantly increased, with mostly the neutrophil component increased, most consistent with infection. Their kidney values, notably the blood urea nitrogen (BUN) and creatinine were significantly affected, indicative of decreased kidney function (and dehydration). And of course, pus in the urine indicating a severe infection. One cat had undergone a surgical procedure a decade ago that essentially turned him into a her. at least externally. He likely had become obstructed on many occasions, or was unable to be unblocked after one serious obstruction. This procedure, called a perineal urethrostomy, is still done from time to time, but not as often as it was in the past. The wider urethral orifice, like that of a female, predisposes the cat to ascending urinary tract infections. Interestingly, the cat was fine for a decade. Perhaps with the cat's advanced age, he is becoming somewhat immunocompromised. He may have had a chronic, mild, sub-clinical infection for quite a while, that ascended his urinary tract to his kidneys.
The other cat, an uncontrolled diabetic, had pyelonephritis and was in DKA (diabetic ketoacidosis). Not a great combination. At first she was diabetic, then uncontrolled, then was hit with pyelo, and the infection threw her into DKA. Ketosis ain't about sugar (glucose). That's how it works.
Over a few days, we got her out of ketosis, treated her pyelo, and turned her into a "regular" diabetic.
After two weeks at home on antibiotics, insulin, and a special diet for diabetic kitties, her insulin requirements are down to almost nil. She will be treated with antibiotics for at least a month. Most importantly, she is back to same ol' kitty she used to be.
We're all very happy with the outcome of these two cases.

Warning: gross photo below:



A kidney severely affected with pyelonephritis.