It is the challenge and difficulty of developing a non-standard disability like FMS that is particularly rewarding. It is, in my opinion, better to approach FMS head on. It is to invite the Administrative Law Judge to look elsewhere. It is to invite disaster. The Administrative Law Judge need not pay a claim if he doubts the credibility of a witness, if the medical evidence is weak, if there is a conflict within the medical record or if there is other evidence which suggests a basis for not granting disability.
Experience suggests that the more narrow the focus, the better the prospects are for prevailing.
Be prepared to speak to the ratio of good days to bad days. That provides insight into the debilitating nature of the syndrome. It is unwise to exaggerate. If the pain level fluctuates, tell the truth. That word is not part of the disability lexicon.