Fibro‐osseous pseudotumor of the digit: a comparison to myositis ossificans by light microscopy and immunohistochemical methods

Abstract

Fibro-osseous pseudotumor of the digit is an unusual cutaneous process characterized histologically by a fibroblastic proliferation admixed with reactive/metaplastic osteoid formation. The osteoid formation can be florid and immature, mimicking the appearance of malignant osteoid-forming neoplasms. Fibro-osseous pseudotumor of the digit has histologic and clinical features in common with myositis ossificans. This has led many to consider the two to be synonymous. We studied three cases of fibro-osseous pseudotumor, compared to five cases of myositis ossificans, using routine light microscopy and a battery of immunohistochemical stains. Both entities displayed a "zoning" pattern of immature spindled areas admixed with more mature areas having osteoid metaplasia. This was more pronounced in myositis ossificans. In each lesion, the spindle cells stained positively for vimentin and actin. CD34 and Factor VIII highlighted the vasculature. No stromal staining for MAK-6 (cytokeratin) or S-100 was identified. Ki-67, a proliferation marker, showed positive staining of the stromal cells in both lesions, which was strongest in the immature spindled areas. The immunohistochemical and histologic similarities of the lesions support fibro-osseous pseudotumor of the digit being a cutaneous variant of myositis ossificans.

Expression of IL-5 alters bone metabolism and induces ossification of the spleen in transgenic mice

“…Clinically, patients have been described with heterotopic ossifications of cutaneous (18,19), intratendinous (20), pulmonary (21), and cochlear and vestibular lumenal (22) sites. Severe examples of dysregulated bone formation include myositis ossificans, a progressive ossification of striated muscle and faciitis (23), and fibrodysplasia ossificans progressiva, which refers to postnatal heterotopic ossification of connective tissue (24).…”

Acral manifestations of soft tissue tumors

“…11 Fibro-osseous pseudotumor of digits Fibro-osseous pseudotumor of digits may become absorbed by the umbrella term myositis ossificans, to which it is microscopically nearly identical. 14,15 Notwithstanding the foregoing, it is discussed here in keeping with the traditional literature. Fibro-osseous pseudotumor of digits is a fast-growing, often painful lesion presenting as a fusiform swelling in the proximal phalanx of the index or middle finger in a young adult.…”

The diagnostic conundrum of Florid Reactive Periostitis: A case report and review of the literature

“…[2,5,7,11] However, it is typically more developed with MO, and thus the zoning with FRP is referred to as incomplete. [5,12,13] Fasciitis-like stroma with fibroblast, osteoblast, osteoclast, moderate cellularity, no atypia and intramembranous woven bone production can be seen with both FOPT and FRP, but unlike FOPT, the ossification center of FRP is attached to bone. [2,14] Histochemically, MO, FOPT, and FRP stain positive for muscular vimentin, actin and the proliferative Ki-67 marker while staining negative for MAK-6, S-100 and desmin.…”

“…[2,14] Histochemically, MO, FOPT, and FRP stain positive for muscular vimentin, actin and the proliferative Ki-67 marker while staining negative for MAK-6, S-100 and desmin. [2,13,15] Even once a presumptive diagnosis is made based on clinical, radiographic and histologic findings, the natural history can be unpredictable as four documented possibilities have been reported. It can spontaneously resolve; be cured after excision, recur in an insidious pattern, or recur more aggressively with surmised aggravation from previous surgical trauma, as in our case.…”

“…Misdiagnosis has occurred, which has led to unnecessary early radical amputations. [8] Many authors contend that FRP is a subcutaneous variant on a continuum with MO, [1,2,6,7,13] but this is not universally accepted. [11,16] Nonoperative non-steroidals or radiation have therefore been suggested as potential treatments.…”