Frequency of plasmapheresis question

I have had CIDP for 13 months. IVIG does not work for me so I receive plasmapheresis followed by the steroid SoluMedrol by IV infusion. Two months ago I went from receiving treatments once every 2 weeks to once every 3 weeks. I notice more tingling in my hands after 2 weeks and 2 days, then when I get the plasmapheresis and SoluMedrol it eases somewhat. Since going to 3 weeks I feel I am not improving. I have increased pain in my feet, my toes are stiffer and I have to be more careful about my left knee buckling when I walk. I feel that I may be going very slowly backwards. I have asked my neurologist about what determines the frequency of my plasmapheresis and if there is a test to determine how often I should get it. He replied “Were flying by the seat of our pants here, if you start falling down again we need to increase the frequency”. I realize it is a rare disease and not much is known about it. He says we need to lengthen the intervals so we can trick my body into not attacking the myelin sheath anymore. Does anybody have any information on protocol of determining frequency of plasmapheresis? Does anybody have any information on any tests or other means to determine the frequency? To anybody getting plasmapheresis: what does your neurologist say? Any help is appreciated.