The problem with muscle biopsies in adults

By the time the adult patient comes to the point where they need a muscle biopsy, all other diagnostic maneuvers have been exhausted. Often, the biopsy is of little to no help and the clinician is left wondering what the diagnosis is. I often find muscle biopsies frustrating because I know that the patient had to undergo minor surgery to have the biopsy done, and then I cannot really do much with the biopsy to help the clinician. Part of it may be my own diagnostic limitations. But, I see the reports of other neuropathologists, and they are also often vague and non-specific as well. I suppose it is helpful when I can identify features consistent with polymyositis. But, when there is a clinical suspicion of polymyositis, what's the harm in a trial of steroids to see if the patient gets better? I realize that an unnecessary course of steroids is not worth the risk in some patients, but in many such a trial would be an acceptable route to go rather than subjecting the patient to biopsy.