DERMATOMYOSITIS: Childhood

Capillary pathology   Alkaline phosphatase Complement deposition Inflammation Perifascicular atrophy Adult pattern

Muscle fiber atrophy: Perifascicular distribution H&E stain	H&E stain
Muscle fibers near the perimysium are small but not necrotic.   Necrotic fibers are more common in adult forms of DM. Nuclei in small muscle fibers are enlarged and occasionally internal.
Batten FE Br J Child Dis 1912;9:247

Other stains showing perifascicular pathology
ATPase pH 9.4 stain	Cytochrome oxidase stain	NADH stain
Perifascicular atrophy is often most prominent on ATPase stains	The extent of the perifascicular muscle pathology in active DM is often most prominent on cytochrome oxidase stain. Perifascicular muscle fibers have reduced staining more commonly in children.	Muscle fibers near the perimysium are small & stain somewhat darkly

Alkaline phosphatase staining: Other vascular & connective tissue pathology
Alkaline phosphatase may stain several different structures in patients with dermatomyositis.
Alkaline phosphatase stain	Alkaline phosphatase stain	Alkaline phosphatase stain
Perimysium Vascular staining. More common in children	Endomysium Capillary staining, especially in perifascicular regions.	Perimysium Diffuse staining. More common in adults Rare in children

Childhood dermatomyositis: Capillary pathology

Stain: Ulex europaeus agglutinin I Dermatomyositis: Capillaries are enlarged and reduced in number Changes are patchy and most prominent in perifascicular regions

Stain: Ulex europaeus agglutinin I Control: Capillaries are abundant and small

Childhood dermatomyositis: Complement deposition in capillaries

Stain: C5b-9 components of complement (Membrane attack complex) Dermatomyositis: C5b-9 deposition in endomysial capillaries Changes are patchy and most prominent in perifascicular regions

Normal control Stain: C5b-9 components of complement (Membrane attack complex) No C5b-9 deposition in endomysial capillaries

Childhood dermatomyositis: MHC Class I upregulation

Stain: MHC Class I Normal: MHC I staining only on capillaries

Stain: MHC Class I Dermatomyositis: MHC I upregulation on the surface and within muscle fibers