Hallo Glencoe,
Sorry to be of no help for your little fellow, never heard of this condition before. But it does sound very unpleasant for him

. Is it some kind of an auto-immune disease? (As you've been prescribed steroids?)
Some dogs are given steroids one tablet every other morning, that way his body also keeps making his own steroids and you might need less steroids and have less side effects. (As the steroids work for about 36 hours, he has 12 hours without the artificial steroids in his body, so his body keeps up his own steroid production.) Mind you, I'm not a medical expert and it doesn't always work (sadly enough not with our dog).
Hope there is someone on COL with more experience with this condition and hope he improves, the poor thing.