Prednisone, The Difficulity of the Biopsy.

Q. Can prednisone cause a false negative result on a muscle biopsy of a patient who has been previously diagnosed with DM?

Dr. Frederick Miller: This question relates to the issue of whether therapy can change the pathology in the muscles of a patient with myositis. Although this question has not been adequately studied in a scientific manner, therapies are given in hopes of decreasing inflammation in affected tissues and making them more normal; and we have seen changes in the MRIs of myositis patients after prednisone that would suggest that therapy can eliminate muscle inflammation in some patients. Another related problem, however, is that the inflammation and other pathological changes in the muscles of myositis patients is spotty and often only occurs in selected muscles or only in certain areas of selected muscles, so that a biopsy from a given site may miss the pathology. On the other hand, the fact that this patient had a biopsy some time after being treated for dermatomyositis, suggests that there may have been some uncertainty about the diagnosis and this also could have resulted in a "negative" biopsy.