First- glad you aren't using Benadryl, because it is not compatible with Prednisone! (ask your friendly pharmacist )

Those filter machines are pretty amazing, aren't they? I hope Tiger starts feeling better...and your asthmatic baby too!

Jenn's cat - was it Jenn's? - had an ear polyp. I don't think she had to resort fo CT scans, though I don't know. Please ask your vet who might be able to have a look for it! They can be kind of...not good!

Of course, if the antihistamine and air restore his balance, then you will know it is sinuses and not a polyp...but try and get that eliminated from the list of possibilities ASAP.