Myositis of chronic graft versus host disease.

A 13-year-old girl with chronic graft versus host disease (GVHD) developed severe proximal weakness. Muscle biopsy showed necrotic fibers with anti-IgG deposits and interstitial inflammation. Steroid treatment helped, but her weakness recurred. Repeat biopsy showed persistent inflammation and possible steroid myotoxicity. Numerical ratio of capillaries to myofibers and capillary numerical density were higher than childhood dermatomyositis (CD), and capillaries had no tubuloreticular inclusions. Absence of quantitative histologic, ultrastructural, or immunocytochemical abnormalities of capillaries differentiated our patient from CD. We conclude that myositis of chronic GVHD can present as a severe myopathy that responds to steroids and differs from CD.