Also, corticosteroids only last as long as your using them. So if this is a chronic thing the prognosis is grim. That's if it actually works. If it's any of the suspected viruses any treatment should be considered pointless and a source of infection outbreak. Corticosteroids don't treat these two viruses as far as I know.

If there was a way to tell for sure that it is swelling then great but I dont think that technology is readily available. CT scans and MRI's are expensive and even then trying to determine if swelling was present from those results would seem extremely difficult. What makes you think its encephalitis?