Skeletal muscle regeneration: report of a case presenting as a cutaneous nodule following blunt trauma to the lip

Abstract

Skeletal muscle (SM) regeneration is a pleomorphic yet benign reaction pattern that follows injury to SM and has been reported to simulate histologically various malignancies such as squamous cell carcinoma and rhabdomyosarcoma. A 61-year-old man presented with a 4-month history of an enlarging nodule on the upper lip following blunt trauma. An initial punch biopsy was non-diagnostic. A deeper biopsy revealed a multilobular proliferation of atypical and pleomorphic cells with vesicular nuclei, prominent nucleoli, and large amphophilic cytoplasm. Immunoperoxidase studies showed these cells to be positive for muscle-specific actin and desmin and negative for S-100 protein and smooth muscle actin. Based on these findings, a diagnosis of skeletal muscle regeneration (SMR) was made. To our knowledge, this is the first report of SMR presenting clinically as a rapidly growing cutaneous nodule on the lip following blunt trauma.

Primary cutaneous rhabdomyosarcoma: Case report and review of published work

“…However, RMS lacks the peripheral maturation pattern observed in SMR. 5 Our case is interesting in that the initial presentation of primary cutaneous RMS clinically resembled an atrophic scar.…”

“…1 Though cutaneous cysts, especially epidermal cysts, are also often observed in cases of NBCCS, 1,2 cutaneous keratocysts are rare. [3][4][5] We report a case of NBCCS with multiple cutaneous keratocysts.…”

“…4 Muscle-specific actin and desmin have been reported as the most sensitive marker, whereas myoglobin, myogenin and MyoD1 are considered to have greater specificity. 5 The differential diagnoses include general categories of tumors with small, round, blue cells. In our case, CD56 positivity made the differential diagnosis with Merkel cell carcinoma and malignant peripheral nerve sheath tumor difficult.…”

Supraorbital Cutaneous Fetal Rhabdomyoma of Intermediate Type

“…Skeletal muscle regeneration can often be seen in biopsies of facial skin because of the presence of superficial skeletal muscle in this anatomic area and can be mistaken for neoplastic processes. 13,14 We also considered rhabdomyomatous mesenchymal hamartoma in our differential diagnosis. Rhabdomyomatous mesenchymal hamartoma is a relatively rare entity that consists of mature skeletal muscle elements admixed with adipose tissue, with increased neural and adnexal elements, and increased collagen fibers 15 that may present in the orbital area in infancy.…”

Orbital rhabdomyosarcoma and traumatic neuroma following enucleation for a uveal schwannoma in a dog: a case report

“…Orbital rhabdomyosarcomas have been reported in humans following blunt traumatic injury to the eyebrow in an adult [26], suspected to be due to aberrant skeletal muscle regeneration (SMR) after injury or inflammation. SMR has also been reported to histologically stimulate cutaneous malignancies such as squamous cell carcinoma and rhabdomyosarcoma in humans [27][28][29].…”