Alternative name: B-Cell Inflammatory Myopathy (BCIM)

    Muscle fiber
      Varied size
    Lymphocyte foci + Vessels
Immune changes
  Cell types
  Endomysial pathology

BCIM inflammation: Lymphocyte foci also containing Vessels

H&E stain
Inflammation: Cell foci
  Cell type: Lymphocytic
  Location: Perimysium; May extend into endomysium
Myopathic changes
  Fiber size: Varied
  Endomysial connective tissue: Variably increased

H&E stain

Lymphocyte focus: Endomysial & Perimysial

VvG stain

Congo red stain
Inflammatory cell focus
  Some lymphocytes are clumped
  Inflammatory cell focus contains intermediate-sized & small vessels
H&E stain

VvG stain

Gomori trichrome stain
Lymphocyte inflammation
  Surrounds & contains intermediate-sized & small vessels
  No elastin fibrils in vessel wall.
  Often in perimysium
  May also be present, or extend into, in endomysial regions within fascicles

Congo red stain

Vessel in region of inflammation
  Endothelial cells: Large; May be Esterase+


BCIM: Cell types in lymphocyte foci

H&E stain
Small dark cells with little cytoplasm surround an intermediate sized, and several small, vessels

CD20 stain
CD20+ B-cells are a prominent component of some perivascular inflammatory foci.

CD4 stain

CD20 stain
CD4 T-lymphocytes in
  endomysial connective tissue

CD20 B-lymphocytes in
  perimysium extending into endomysium

CD4 stain
CD4 T-lymphocytes
  Present in perimysium, extending into endomysium

CD20 stain
CD20 B-lymphocytes
  Present in subset of inflammatory foci
Serial sections: B-cell foci are present in some but not all (arrow) regions of CD4 cellularity

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 phosphatase positive histiocytic cells: Acattered through the cell focus
Most cells in focus are Acid phosphatase negative

Inflammatory foci contain vessels

CD31 stain
CD31+ endothelial cells are present in
  Small vessels within perivascular inflammatory foci
  Lumen of intermediate-sized vessel
Vessels stain for ATPase (Below)

ATPase pH 4.3 stain

Esterase stain
Intermediate-sized vessels in inflammatory foci
  Endothelial cells are large (Below) & stain for esterase (Above, arrows)

VvG stain

BCIM: Endomysial pathology

Complement Deposition (C5b-9; MAC) on endomysium

C5b-9 stain

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

C5b-9 deposits
  Endomysial connective tissue
  Necrotic muscle fibers: Cytoplasm

C5b-9 stain

IgM: Deposited on endomysial connective tissue

IgM stain

Brachio-Cervial Inflammatory Myopathy: Myopathic changes

H&E stain
Muscle fiber necrosis   Muscle fibers in varied stages of necrosis & regeneration

H&E stain
Necrotic muscle fibers: Scattered

H&E stain

Necrotic muscle fibers in varied stages of phagocytosis by histiocytic cells

Acid phosphatase stain

Muscle fiber necrosis: Changes in individual muscle fibers

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: CD68+ histiocytic cells invading fiber

CD68 stain
Segmental muscle fiber necrosis: CD68+ histiocytic cells

CD68 stain
Muscle fiber necrosis: CD68+ histiocytic cells replacing part of a fiber

BCIM: Myopathy, Varied muscle fiber size

Chronic-Severe myopathy
  Varied fiber size
    Bimodal distribution
    Small muscle fibers: Rounded or Polygonal
  Large muscle fibers: Mild hypertrophy
  Internal nuclei: Scattered muscle fibers
  Endomysial connective tissue: Mildly increased

H&E stain

Mild-Moderate myopathy: Varied fiber size
  Fiber sizes: Bimodal distribution
  Type 1 & Type 2 fibers are small and large.

H&E stain

ATPase pH 9.4 stain

BCIM: Muscle fiber Regeneration & Immaturity

H&E stain

ATPase pH4.3 stain
Basophilic regenerating muscle fiber Many Type 2C immature or regenerating muscle fibers

H&E stain

Basophilic regenerating muscle fiber: Contains bluish cytoplasm & large nuclei

BCIM: Immature muscle fibers, Many, Small size

ATPase pH 4.3 stain
Many muscle fibers are type 2C with intermediate staining.

ATPase pH 4.3 stain

Immature, small muscle fibers: Cytoplasm stains with alkaline phosphatase

Alkaline phosphatase stain

Immature, small muscle fibers: Cytoplasm stains darkly with NADH

NADH stain

Immature, small muscle fibers: Cytoplasm stains pale with AMPDA

AMPDA stain

BCIM: Focal invasion of muscle fibers by mononuclear cells
  Present in some patients

Acid phosphatase stain

CD4 stain
Focal invasion of muscle fibers

  Upregulation on muscle fibers, especially surface
  Expressed on cells in inflammatory foci

MHC Class I stain

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