FOCAL MYOSITIS

H&E stain	H&E stain	H&E stain
Muscle morphology Perimysium is markedly widened. Perimysium is populated by large cells with surrounding clear area. Necrosis & fragmentation of perimysium is not prominent vs. fasciitis

Perimysial pathology H&E stain Perimysium is invaded by inflammatory cells.

H&E stain Some areas of connective tissue are sworled or disrupted.

H&E stain	H&E stain	H&E stain
Endomysial pathology Muscle fibers have varied size. Small fibers are rounded. Edema may be present between muscle fibers. Some mononuclear inflammation can occur(Right).

Alkaline phosphatase stain	Acid phosphatase stain
Inflammation Alkaline phosphatase strongly stains perimysium & endomysium. Acid phosphatase staining cells in the perimysium are less common than in fasciitis (Right).