My senior tortie girl is about 16 years old now. She has a diagnosis of hyperthyroidism from 3 years ago, it's well controlled by Vidalta. In the past few months she developed symptoms that made me think her thyroid levels were probably high again - constantly hungry, drinks and pees a lot, excessive meowing, shedding a lot of hair, a bit grumpy, and slowly losing weight (about 500 grams in the past 6 months but she is a bit overweight so she is still not thin).
Blood tests two weeks ago came back all fine - thyroid is lower end of normal (both the usual T4 and free T4 tests), renal values are just a tiny bit above normal range, similarly glucose was just a smidge high but vet wasn't concerned. Everything else normal. Vet did the tests under sedation because my girl is so difficult to handle and she also checked teeth (a bit of tartar but fine) and felt her body all throughout (no lumps or bumps, skin looks fine etc.). Heart and lungs sound fine. Impossible to check blood pressure because of her behaviour, though.
So all the usual issues have been ruled out (thyroid, renal, diabetes) but she still continues to slowly lose weight (another 30-50 grams since the vet visit, I have really accurate baby scales for weighing) but has a great appetite. She is still shedding A LOT of hair, being very vocal but generally appears bright and fine.
I'm thinking something that causes malabsorption so that she's not taking in the nutrients from her food? I also worry about cancer but as she has such good appetite and is not lethargic, that seems unlikely? Poo is fine in consistency although seems more smelly than in the past, so maybe something intestinal is possible?
Vet has said next step could be xray or ultrasound but it would have to be another sedation as my cat is impossible to handle otherwise at the vet's.
Has anyone come across something that presents such as hyperthyroidism but thyroid levels are fine in blood test? Vet seems all out of ideas at the moment.