Neuromuscular

Inflammatory Myopathy with Abundant Histiocytic Cells (IMAM)

Cell Foci Muscle Fibers Differential Diagnosis

H&E stain

IMAM: Lesions

  Locations: Perimysium & Endomysium
  Cells: Mostly large & Histiocytic; May contain sub-foci of non-histiocytic cells (Arrow)

H&E stain

H&E stain


H&E stain

IMAM: Clusters of Histiocytic cells


VvG stain

IMAM: Smaller lesion confined to perimysium

VvG stain

IMAM: Vascularization

Cell foci often contain smaller vessels, some with thick basal lamina

VvG stain

Vessels in perimysial cell foci stain for Ulex

UEAI stain

Alkaline phosphatase stain
Vessels in cell foci stain for Alkaline phosphatase & ATPase

ATPase pH 9.4 stain

IMAM: Cell Foci

  Large cells with abundant cytoplasm
  Location: Perimysium > Endomysium


H&E stain



H&E stain



H&E stain
IMAM Cell Foci
  Large cells with abundant cytoplasm
  Location: Perimysium > Endomysium

Gomori trichrome stain



Congo red stain
IMAM cells
  Cells: Large
  Nuclei: Large; Irregular shapes

VvG stain


Histiocytic cells

  Acid phosphatase positive
  Confluent staining


Acid phosphatase stain

Histiocytic cells:
  May extend from perimysium into endomysium

Acid phosphatase stain

Esterase stain

IMAM cells in perimysium: Contain lipid
  Dark on Sudan
  Gray on VvG


Sudan black

VvG

IMAM perimysial cells: May be PAS positive

PAS stain

IMAM: MHC Class I

Cells in foci: Strong staining
Muscle fibers: Upregulation by morphologically normal fibers

MHC Class I stain

IMAM: Cell Types


CD68 stain
Cells in foci: Strong staining for CD68

CD68 stain


CD3 stain
Cells in foci: Little staining for CD3 or CD20

CD20 stain

IMAM: Ultrastructure


From: R Schmidt

From: R Schmidt

From: R Schmidt

From: R Schmidt

From: R Schmidt

From: R Schmidt

From: R Schmidt

Return to Inflammatory myopathies
Return to IMAM

11/30/2021