Light microscopy of muscle biopsy. A: Modest variability in myofiber diameter with scattered angular atrophic fibers (hematoxylin-eosin staining). Rimmed vacuole is shown at higher magnification (insert). B: Atrophic fibers with rimmed vacuoles (arrow, modified Gomori trichrome staining). C: Granular pigment-containing histiocytes in endomysial areas and rimmed vacuoles showing high acid phosphatase activity (compared to the rimmed vacuole on modified Gomori trichrome staining [insert]). D: NADH-tetrazolium reductase reaction shows dark-brown depositions in myofibers and vacuoles (compared to the rimmed vacuole on modified Gomori trichrome staining [insert]). E: Histiocytic pigment stained bright blue with Prussian blue. F: Histiocytic pigment stained black on a Masson Fontana preparation.