BRACHIO-CERVICAL INFLAMMATORY MYOPATHY (BCIM)

Muscle fiber necrosis

H&E stain Muscle fibers in varied stages of necrosis & regeneration H&E stain Early necrosis: Dark muscle fiber with loss of cytoplasmic structure H&E stain Later stage of necrosis: Muscle fiber invaded by cells with large nuclei and abundant foamy cytoplasm H&E stain Later stage of necrosis: Collapsed muscle fiber largely replaced by cells CD68 stain Muscle fiber necrosis with CD68+ histiocytic cellularity invading fiber CD68 stain Segmental muscle fiber necrosis with CD68+ histiocytic cellularity CD68 stain Muscle fiber necrosis with CD68+ histiocytic cellularity replacing part of a fiber

BCIM: Varied muscle fiber size

ATPase pH 9.4 Varied fiber size: Type 1 & Type 2 fibers are small and large.

ATPase pH 4.3 Many muscle fibers are type 2C with varying degrees of intermediate staining.

BCIM: Regeneration
H&E stain	ATPase pH4.3 stain
Basophilic regenerating muscle fiber	Numerous Type 2C immature or regenerating muscle fibers
H&E stain Basophilic regenerating muscle fiber: Contains bluish cytoplasm & large nuclei

BCIM: Myopathic changes with varied muscle fiber size
H&E stain	H&E stain
Chronic myopathy Varied fiber size: Small muscle fibers are rounded Scattered muscle fibers with internal nuclei Increased endomysial connective tissue, mild Muscle fiber damage: Necrosis (Right) & Focal invasion (Below)

BCIM: Focal invasion of muscle fibers by mononuclear cells
Acid phosphatase stain	CD4 stain
Focal invasion of muscle fibers

BCIM: Inflammation around vessels in perimysium
H&E stain	GT stain
Perivascular inflammation with myopathic changes, including varied fiber size and increased endomysial connective tissue,

Mononuclear cell inflammation typically surrounds intermediate-sized perimysial vessels with no elastin fibrils in their wall. VvG

VvG

Cell types in perivascular inflammation

H&E stain Small dark cells with little cytoplasm surround an intermediate sized vessel CD20 stain CD20+ B-cells are a prominent component of some perivascular inflammatory foci. CD3 stain A minority of the perivascular cells stain for CD3 (T-cells) CD68 stain CD68+ macrophages are scattered through the infiltrate and in neighboring connective tissue Acid phosphatase stain Acid phosphatease positive histiocytic cells are scattered through the perivascular infiltrate CD31 stain CD31+ endothelial cells are present in small vessels within the perivascular inflammatory focus and in the lumen of the intermediate-sized vessel Esterase stain Endothelial cells in intermediate-sized vessels are enlarged & stain for esterase (arrows)

BCIM: Other inflammatory cells
CD4 stain	CD20 stain
CD4 positive mononuclear cells in   endomysial connective tissue	CD20 positive B-cells in perimysium & endomysium

CD4 stain CD4 positive mononuclear cells present in endomysium & perimysium	CD20 stain CD20 positive B-cells present in focal regions
Serial sections: B-cell foci are present in some but not all (arrow) regions of CD4 cellularity

BCIM: Complement Deposition (C5b-9; MAC)

C5b-9 stain	C5b-9 stain
BCIM muscle: CD5b-9 components of complement   are deposited in endomysial connective tissue	Control muscle: No CD5b-9 components of complement   are deposited in muscle