severe pain ankles and achilles

I have a patient presenting in my clinic with severe ankle and achilles pain to feet bilaterally.  Small amount of  swelling noted, but not extreme.  All of the testing is so far negative....sed rate normal; ana norma; white count is normal even a ck is normal.  She is in excrutiating pain and i am at a loss on how  to help her or which way to go.  Trial of antiinflammatories was unsuccessful in relieving pain, tramadol doesnt work, tylenol # 3 isnt working.  I hate to just keep giving pain med to mask the issue.  Just dont really know where to go next.  She is on Predisone 10 mg daily, with no relief from that either.  It has progresses quickly ( within 2 weeks time) of her being able to care for herself, to being dependent on others, due to the degree of pain makes walking too painful.  I feel like this is probably one of  the rhuematological processes that doesnt follow the book or an infllammatory process. But I am stuck

I hope someone else has some ideas that they may share with me. Thanks