CLINICAL CASES   

Giornale Italiano di Dermatologia e Venereologia 2003 February;138(1):41-5

Copyright © 2003 EDIZIONI MINERVA MEDICA

language: English

Skeletal muscle regeneration. Report of a case simulating squamous cell carcinoma

Stefanato C. M. ¹, Mahalingam M. ^{2, 3}, Kates S. G. ⁴, Bhawan J. ¹

¹ Dermatopathology Section Department of Dermatology Boston University School of Medicine Boston, MA, USA 2 Quest Diagnostics Incorporated Cambridge, MA, USA 3 Department of Pathology Boston University School of Medicine Boston, MA, USA 4 Division of Dermatology Department of Medicine University of Massachuttes Medical Center Worcester, MA, USA

A 70-year-old male presented with a 6-month history of a 5x2 cm indurated sclerotic lesion on the left temple. An excisional biopsy specimen revealed squamous cell carcinoma. Because of positive margins, re-excision was performed which showed residual squamous cell carcinoma infiltrating the skeletal muscle. A third deeper excision showed ulceration, scar, and a dense proliferation of small atypical cells in the skeletal muscle, with perineural infiltration and occasional mitoses. The atypical cells had large irregular vesicular nuclei, prominent nucleoli and occasional multinucleation. These findings were felt to be suggestive of residual infiltrating squamous cell carcinoma. However, the cells of the infiltrate were negative for both cytokeratin and S100 protein but positive for muscle markers (muscle-specific actin, desmin, Myo-D1, and myogenin), indicating myogenic lineage. Skeletal muscle regeneration is a pleomorphic but benign reaction pattern that may mimic malignancy, and consequently be a diagnostic pitfall, especially in the absence of a complete clinical history. This pattern should be considered in the differential diagnosis of atypical cellular infiltrates in the skin, when they occur within previously injured skeletal muscle from prior excisions.