Cat starving itself - Answered by Dr. Van Lienden

[Pink Panther]

I live in Grenada, West Indies, where there is not a lot of veterinary help - but there IS a veterinary training school! However:

Jess (aged 13? neutered female) stopped eating about a year ago. It is as if she has ceased to recognise food. She is starving, crying for food by day and night,and has lost weight alarmingly. Sometimes she is so weak that she just staggers. She refuses dry cat food (which she's eaten for years), tinned food (which she's never liked), cheese, milk, chicken (cooked / uncooked), mincemeat, eggs and all but one kind of fish. These fish are called 'jacks', are a bit like sardines, and have become very difficult to obtain.
My other cat eats everything she leaves, and is becoming pony-sized. So the food is OK!
Routine: Jess screams for food, I give her any of the above, (except jacks, which are usually acceptable); she glances at the food and resumes screaming that she's starving.
At the veterinary training school, she has had three blood tests: nothing abnormal except high white cell count, so fighting infection?
They've taken some (infected) teeth out: no change.
They put her on steroids: very effective at first, but decreasingly: and if she eats, she is clearly in pain shortly afterwards. Jacks seem to cause least pain.
She has been scanned and x-rayed: nothing found.
Thyroid, diabetes, blockages ruled out.
Copious vomiting follows any overenthusiastic eating: sometimes she will eat something recently untried, but either vomits it out, or goes off it after about two days.
Somehow, she summons the energy to catch grasshoppers and even the odd mouse, which she eats greedily and completely. (And then sometimes but not always vomits out again.)
I thought that strong-smelling foods were most likely to be 'recognised' as edible, but she is inconsistent.
When 'jacks' are available, she relaxes, and puts on a little weight. But I can only get enough to freeze for about a fortnight at a time, and she sometimes goes off jacks too within this time..
She usually drinks a lot (water)
Ideas, please! Jess has been a good friend to me over so many years. Many times I have been on the verge of having her put down , but then she rallies strongly for a few days. The medical school vets (she has been seen by three) say 'We are running out of diagnostic options', which means they don't know!
thanks.