The reason pred is used at onset of symptoms is because cranial nerve pathologies, especially acute onset, could be down to herpes simplex or zoster infection and the associated inflammation. Of course the list of differentials is huge, and imaging is mandatory, and if you can get an MRI immediately and then consider treatment then that would be the best course of action. But the neurological consequences of untreated herpes infections of the cranial nerves can be ameliorated with prompt corticosteroid use (and antiviral use, especially in Ramsay Hunt syndrome). I cannot think of a differential that would be made worse by initiating prednisolone whilst you wait for the MRI.
And Sully, shame on you for insulting generalists! I would be mad except you're a hero of mine for your pioneering work with the old folk and I'm secretly pleased to have been involved in a forum discussion with you and Rip. Keep up the good work!
Eric I hope things are settling down. Most of the time this isn't anything serious. But I agree in this day and age a scan is probably reasonable.