FIGURE 6.

Myonecrosis and regeneration. A wide range of histopathology representing the entire spectrum of acute muscle fiber necrosis through regeneration may be seen in any necrotizing myopathy regardless of the etiology. (A) In a single high-power field, this muscle photomicrograph illustrates acute necrosis (#1), early invasion of a necrotic fiber by phagocytic macrophages (#2), numerous macrophages nearly filling the space originally occupied by sarcoplasm (#3), and early regeneration at the periphery of muscle fibers still containing macrophages (#4). (B) Dual label immunofluorescence for collagen VI (green) and perlecan (red) illustrates that the muscle fiber basal lamina (yellow) is largely intact during myonecrosis/regeneration in this dystrophic muscle biopsy. Macrophages clustered inside a necrotic muscle fiber (#3) are very similar to those illustrated in the hematoxylin and eosin-stained cryosection in panel A, #3; some DAPI-positive nuclei may be myoblasts as seen in panel A, fibers labeled #4. Nuclei are blue (DAPI). The scale bar is 50 µm for both A and B.