Proliferative Fasciitis/Myositis
Elizabeth A. Montgomery, MD
Key Facts
Terminology
Tumefactive subcutaneous (fasciitis) or intramuscular (myositis) proliferation featuring ganglion-like fibroblasts
Macroscopic Features
Usually 2-3 cm
Microscopic Pathology
Mostly plump stellate to spindled fibroblasts and myofibroblasts
Large ganglion-like fibroblasts
Macronucleoli, abundant amphophilic cytoplasm
Mitotic activity common
Pediatric examples can display exuberant mitotic activity, which can lead to misinterpretation as sarcomas
 Hematoxylin & eosin shows proliferative fasciitis at low magnification. It tracks along fibrous septa and is somewhat less cellular in the center  , where there is keloid-like collagen. |
 Hematoxylin & eosin shows the so-called ganglion-like cells  of proliferative fasciitis. These are fibroblasts, but their macronucleoli are reminiscent of those found in ganglion cells. |
TERMINOLOGY
Definitions
Tumefactive subcutaneous (fasciitis) or intramuscular (myositis) proliferation featuring ganglion-like fibroblasts
Background of myofibroblasts and fibroblasts similar to those in nodular fasciitis
CLINICAL ISSUES
Epidemiology
Incidence
Rare; less common than nodular fasciitis
Age
Middle-aged and older adults; rare in children
Gender
No predominance
Site
Proliferative fasciitis: Upper extremity (forearm) > lower extremity > trunk
Proliferative myositis: Trunk > shoulder girdle > upper arm > thigh
Presentation
Rapidly growing painless mass; more likely to be painful than nodular fasciitis
Usually no history of trauma
