Surgical Pathology Criteria

Proliferative Myositis

Differential Diagnosis

Proliferative Myositis differs from Proliferative Fasciitis only by location

 

Proliferative Myositis Nodular Fasciitis
Ganglion-like cells present No ganglion-like cells
No damage to muscle fibers resulting in a checkerboard pattern with lesional cells between patches of intact muscle Muscle fibers obliterated or damaged
Nodular fasciitis may occasionally involve muscle

 

Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Proliferative Myositis
Muscle fibers damaged or obliterated Muscle fibers not damaged
Muscle fibers at edge of lesion Muscle fibers throughout
No ganglion-like cells Ganglion-like cells present
Predominantly collagenous Predominantly myxoid
Usually >3 cm Usually <4 cm
Both involve muscle

 

Rhabdomyosarcoma Proliferative Myositis
May have cross-striations No cross-striations
Cytoplasm typically eosinophilic Cytoplasm typically basophilic
Desmin, myogenin positive Desmin, myogenin negative
Cytologically malignant Lacks malingnant cytologic features
Atypical mitotic figures may be present No atypical mitotic figures
Usually >4 cm Usually <4 cm

 

Ganglioneuroma or Ganglioneuroblastoma Proliferative Myositis
Rarely involves skeletal muscle Involves skeletal muscle
Fibrillar background Myxoid background with reactive myofibroblasts
S100 may stain satellite cells S100 negative
Actin negative Ganglion-like cells may be actin positive

 

Malignant Neoplasm, NOS Proliferative Myositis
Muscle fibers damaged No damage to muscle fibers
Cytologically malignant Lacks malignant cytologic features
Atypical mitotic figures may be present No atypical mitotic figures
Usually >4 cm Usually <4 cm
Malignant neoplasms may occasionally separate muscle fibers in a checkerboard pattern

Stanford Medicine Resources:

Footer Links: