P-COX

Inflammatory Myopathies with Vacuoles, Aggregates & Mitochondrial Pathology (IM-VAMP)

Myositis with mitochondrial pathology (PM-Mito) subtype

Inflammation
Endomysial
Focal invasion of muscle fibers
Myopathic changes
Mitochondrial disorders
Other

Variant syndrome
IBM

PM-Mito: Muscle pathology

Myopathy: Fiber sizes vary from small to hypertrophic
Mitochondrial pathology: 2% to 27% of muscle fibers
Endomysial inflammation
Focal invasion of muscle fibers by inflammatory cells
mtDNA deletions (90%): Multiple
Aggregates in muscle fibers: LC-3; αB-crystallin ⁵⁸
No vacuoles or SMI-31 aggregates

PM-Mito: Myopathy, Inflammatory

VvG stain

Muscle fibers
Sizes: Varied; Largest fibers hypertrophied
Internal nuclei
Immature
Small, Darker stained cytoplasm, Large nuclei
Distribution: Scattered
Connective tissue, endomysial
Increased, mild to moderate
Inflammation
Endomysial lymphocytes
Some focal invasion of muscle fibers

H&E stain

Gomori trichrome stain

PM-Mito: Myopathy, Inflammatory

H&E stain

Gomori trichrome stain

PM-Mito: INFLAMMATION

H&E stain

Cell foci: Predominantly Endomysial

Focal invasion of muscle fibers by immune cells

H&E stain

Cell foci contain: Lymphocytes & Histiocytes (Acid phosphatase positive)

Acid phosphatase stain

IM-VAMP: MITOCHONDRIAL CHANGES

Cytochrome oxidase (COX) negative muscle fibers

Cytochrome oxidase stain

Succinate Dehydrogenase (SDH) positive muscle fibers

SDH stain

PM-Mito: Other features

Perivascular Inflammation: Occasional	MHC-I Upregulation on sarcolemma: Diffuse
LC-3 aggregates in muscle fibers

PM-Mito: Capillary pathology

Capillary sizes: Some are large
Endothelial cells: May stain for acid phosphatase (Dark arrow)
Neighboring histiocytic cells (White arrow)

Acid phosphatase stain

Return to Inflammatory myopathies
Return to Polymyositis with mitochondrial disorders

7/18/2021