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Soft Tissue Pathology Online

Reactive Fibrous Proliferation

Dr Sampurna Roy MD

Pathology Quiz Case 45 - Case history and images

Diagnosis: Proliferative Myositis





Pathology of Proliferative Fasciitis and Proliferative Myositis

These benign lesions affect older patient than nodular fasciitis (rarely occurs in children).

The lesions may occur either in superficial soft tissue (proliferative fasciitis) or in skeletal muscle (proliferative myositis).

Proliferative fasciitis is common in the extremities, specially in the lower limb. Proliferative myositis is common in shoulder girdle and upper trunk.

Grossly, proliferative fasciitis resembles
nodular fasciitis.

Proliferative myositis is a poorly defined scar-like lesion involving muscle and overlying fascia.

In both conditions, there are clusters of rounded basophilic fibroblasts with prominent nuclei and nucleoli (ganglion-like) which blend with areas showing usual features of nodular fasciitis.

However, the stroma is more myxoid and fibrinoid areas may be present.

In proliferatiive myositis an additional feature is poorly demarcated fibroblastic proliferation involving the epimysium, perimysium and endomysium in a checkerboard-like fashion.

Immunohistochemistry reveals that the ganglion- like cells express vimentin and lack actin or desmin.

Immunohistochemistry and electron microscopy confirm the mixed fibroblastic and myofibroblastic nature of these lesions.

Images of Proliferative Myositis:

Differential diagnosis:

Carcinoma, melanoma or large cell lymphoma in adults .

Rhabdomyosarcoma and even ganglioneuroblastoma in children.

These entities are separated by clinical appearance and by immunohistochemistry.

Acral myxoinflammatory fibroblastic sarcoma is a low grade sarcoma of extremities which can involve joints and tendon sheaths.

This multinodular tumour consists of fibrous areas with marked inflammation,  vacuolated cells and mononuclear or binucleated Reed-Sternberg-like cells.

Ganglion cell like fibroblasts are present in:

Proliferative fasciitis ; Proliferative myositis ; Ischemic fasciitis.         

Acral myxoinflammatory fibrosarcoma ; Inflammatory fibrosarcoma / inflammatory myofibroblastic tumour



Further reading

Fine needle aspiration cytology of pseudosarcomatous reactive proliferative lesions of soft tissue.

Proliferative myositis and fasciitis. A light and electron microscopic, cytologic, DNA-cytometric and immunohistochemical study.

Proliferative fasciitis of the forearm: case report with immunohistochemical, ultrastructural  and DNA ploidy studies and a review of the literature.  

A case of proliferative fasciitis in the abdominal region.

Proliferative fasciitis. Report of a case with histopathologic and immunohistochemical studies.

Aspiration cytology of proliferative myositis. A case report.

Proliferative fasciitis and myositis of childhood.

Proliferative myositis. An immunohistochemical and ultrastructural study.

Proliferative myositis and fasciitis. Report of five cases with an ultrastructural and immunohistochemical study. 

Proliferative fasciitis.


Ischemic Fasciitis (Atypical Decubital Fibroplasia)


Ischemic fasciitis was first described by Montgomery et al (abstract ) in 1992 as atypical decubital fibroplasia and was subsequently termed ischemic fasciitis by Perosio and Weiss (abstract) .

Ischemic fasciitis  predominantly occurs in elderly patients who are physically debilitated or immobilised.

The common sites include soft tissues of  the shoulder, posterior chest wall, sacrum, greater trochanter, buttock, thigh and arm.

The patient usually has a short history of 3 weeks to six months.

Lesions are located in the deep subcuti and occasionally extended into the muscle. Extensive epidermal epidermal ulceration is absent.

Microscopically, there is a  lobular arrangement of zones of  of fibrinoid and coagulative necrosis with fibrin thrombi and spindle cells in a prominent myxoid stroma rimmed by ingrowing ectatic thin walled vessels.

The spindle cells are focally atypical with large hyperchromatic nuclei, prominent nucleoli and basophilic cytoplasm resembling those of proliferative fasciitis.

Fat necrosis is seen at the periphery.

Immunohistochemistry: Two thirds are actin positive, and half are CD34 positive. Desmin is negative.

Differential diagnosis:

1. Decubitus ulcer has more extensive ulceration overlying granulation tissue without zones of necrosis, a myxoid stroma or atypia.

2. Proliferative fasciitis lacks the zonal architecture , vascular features and peripheral granulation tissue.

3. Epithelioid sarcoma is subcutaneous with central necrosis but in more discrete nodules and cytologically bland and epithelial markers are positive.

4. Myxoid malignant fibrous histiocytoma lacks the zones and is more pleomorphic and cellular with a typical vascular pattern.

5. Acral myxoinflammatory fibroblastic sarcoma has inflammation, large polygonal cells with prominent nucleoli and myxoid nodules with vacuolated fibroblasts.

6. Myxoid chondrosarcoma is multilobular and has more uniform bland cells , often in a lace-like pattern, a hyaluronidase-resistant, more myxoid and less necrotic stroma with haemorrhage, glycogen in cells and S100 protein positivity.

7. Myxoid liposarcoma has a striking vascular pattern with lipoblasts and is extremely rare in the subcutis.


Further reading:

Atypical decubital fibroplasia with unusual histology.

Ischemic fasciitis. Report of a case with fine needle aspiration findings.

Atypical decubital fibroplasia: a series of three cases.





Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)








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