Hyperthyroidism and diarrhea

My cat is a 14 year old female and was diagnosed with hyperthyroidism a few months ago. One of the side effects she has been experiencing is daily diarrhea. She does not use the litterbox when this happens and likes to hide it in the basement. 

She was put on methimazole and that helped with both weight loss and cleared up the diarrhea as well. Unfortunately, she also developed anemia and had to be taken off the medication. She's been off of methimazole since early January. Was on a course of antibiotics for a couple weeks to clear up an infection and had subsequently been given radioactive iodine treatment about three weeks ago. 

It appears the treatment worked as her thyroid shrank visibly and she has gained a pound of weight (she was down to 4lbs before treatment). Unfortunately the diarrhea has not cleared up and I don't really see any signs of it clearing up. 

Does anyone have a similar experience? Any advice? She uses the litterbox fine otherwise. I would settle for her using the litterbox consistently instead of going in the basement

I have three litterboxes: one in the basement and two upstairs. She sometimes uses any one of them, but I can't figure out a pattern. She will sometimes go on the floor even if the litterbox is pristine and we do   clean them about 3-4 times a day. 

Appreciate any advice! 

I would advise calling the vet clinic that did her I-131, since you are only three weeks post-I-131, to see if they can give you any information regarding this. FWIW, it takes quite awhile for kitties to get back to their pre-hyperthyroid state, so her little body is going through a lot of changes. This could also be why she still has diarrhea post treatment, but I would ask the vet to be more sure.

Did, or has, she had problems with diarrhea in the past (before her hyper-T)?

Other possibilities are any change in diet, a bad batch of canned food, grains in food, change in formula of food that you're feeding, to name a few.

Since I am more holistically oriented , for the diarrhea you could syringe SEB gruel (the consistency of runny snot ) 3-5 times a day, 5-10mL each time. You can also add it to a small meal if kitty isn't too keen on syringing, but wait 30-60 minutes before or after any medications. It is so soothing and helps with any number of kitty related issues, including diarrhea:

http://www.littlebigcat.com/health/slippery-elm/

"In the gastro-intestinal tract, Slippery Elm acts directly. It can be thought of as a sort of natural  “Pepto-Bismol.” (Pepto-Bismol itself should not be used because it contains salicylate, a.k.a. aspirin). Its mucilage content coats, soothes, and lubricates the mucus membranes lining the digestive tract. Slippery Elm is an excellent treatment for ulcers, gastritis, colitis, and other inflammatory bowel problems. It is high in fiber, and so helps normalize intestinal action; it can be used to relieve both diarrhea and constipation. ..." [my emphasis--underlining--added]

Headbutts!

Jules

P.S. Can't wait until I have enough posts to have a "real" signature.