A little Internet search showed that if your wheelchair meets the criteria for Medicare coverage or was purchased for you by Medicare, and you have ALS, and you are having difficulty in shifting your weight, you have all you need. If the wheelchair is not of a type that Medicare would have covered, there may be a denial. Basically the pwc has to have a seat cushion that can be removed so that a ROHO or other adjustable cushion (air or fluid filled and therefore pressure adjustable) can be placed directly on the seat pan of the chair. Your wheelchair provider should be able to file and get you a cushion. Websites such as SpinLife will get your cushion for you quickly and help with the claim paperwork, but you have to pay upfront and wait for reimbursement.