PMR steroid taper

Hi , Any advice or ideas appreciated. I have had PMR just over 2 years now. Have been on prednisolone since. With numerous alternatives tried with no success.Finally on a biologic Toxcilumab, which has totally changed my CRP markers to now showing no inflammation. I am still on Prednisolone also.
My query is if anybody can offer advice,. I am trying to taper off currently 8.5mg from 15mg in two months. Since the taper and introduction of toxcilumab once a week I have developed rather painful lower back pain all other aches are very mild almost non existent. Could this lower back pain possibly be related to tapering to quick. Any ideas.

Thanks