DERMATOMYOSITIS: Variant Pattern

General features

Muscle Fiber Pathology H&E stain Necrotic & Regenerating muscle fibers in perifascicular regions Muscle fiber size is variable
Muscle Fiber Internal Architcture NADH stain Muscle fibers near the perimysium are small & stain darkly
Hydrolytic enzyme stains
Acid phosphatase stain Acid phosphatase stained cells in necrotic muscle fibers	Alkaline phosphatase stain Alkaline phosphatase stained perimysial connective tissue

Inflammation: Perimysial & Perivascular
H&E stain	H&E stain	Acid phosphatase stain
Foci of Inflammatory cells are not always found in dermatomyositis. They are more common in adults with DM. When present they may occur In the perimysium (center) Or as a cuff around small or intermediate-sized vessels (left) Acid phosphatase stain highlights some perimysial cellularity (right).

Cytochrome oxidase stain

Muscle fibers in regions of perifascicular atrophy,
retain COX activity unlike the childhood pattern