18 yr old cat wont eat

Question
My cat is 18 years old.  I took her into the vet about 6 months ago since she was losing weight and also for an overall checkup.  The vet did a variety of blood tests.  The tests showed that everything was good.  She didn't have diabetes.  Her kidney and liver were functionally normal.  Everything seemed normal.  He recommended doing a T4 test and that showed that she had hyperthyroidism.  She went on medication and was doing great.  We had the T4 done again after several months and her thyroid was functionally normally, which was great.  It's been a month now and she is not eating and is getting weaker.  Two days has passed and she has not eaten anything.  She sniffs the food and turns away (by the way, she eats Iams which the vet said is a good choice).  I went and bought some Iams moist food in the cans and she ate that up really quickly.  I know she's getting old but what is going on with her?  Do you think you can help?

Answer
Hi Olga.  I would say to get her to the vet again.  I know it seems like she's going frequently, but geriatric cats do require more vet care than younger ones.

Sometimes correcting hyperthyroidism can reveal kidney failure.  This is because when treated, the metabolism slows down.  And when the metabolism slows down, waste products are not removed from the body as quickly.  Then the kidneys end up having to compensate to try to get rid of it all.  This recently happened with one of my cats.  So I would suggest having another kidney level test run, perhaps.

It really could be something as simple as an infection somewhere that's making her feel poorly or a bad tooth that makes eating hard food painful.  But certainly, with such a drastic change in eating habits, something is wrong.