I just read an update on housefly's post on the Ask A Vet Expert Forum. It's good news the dog responded to treatment with Prednisone.
That doesn't mean it would be suitable for your dog....I don't know. The best thing to do is take a look at that post (there's a link to it right underneath this one under "related discussions")
You could read this, and then have a word with your vet?
I have an 8 year old bearded collie that has had a temperature of 40.5 for about 4 weeks now. We had blood tests done for Lyme disease and may other tick related diseases plus kidney and liver. We put him on doxicycline for lyme as we waited for the test results. Turns out everything is normal, no lyme, and the pills made no difference to the fever. We tried cephalexin to no avail, and our last attempt at antibiotics is zeniguin. I thought because he has become rather lame, his legs give out occasionally, that it would have been lyme. He eats at least, half of his normal amount. What has happened to your dog? I see by the date it was a while ago, today is June 25 2010. Anyone have any advice?
Also, I read on another site about four other tick diseases, Ehrlichia, Rocky Mountain Spotted fever, Anaplasmosis and Babsesia. Has your dog been tested for these? Good Luck.
I know years ago Lyme tests could come back false negative, have they improved them since then, or could that still be possible with your dog?