Expression of desmin and smooth muscle myosin heavy chain in dermatofibromas.
BACKGROUND
The histopathologic features of dermatofibroma vary remarkably, and this diversity may occasionally cause problems in differentiating between benign and malignant mesenchymal lesions, including smooth muscle neoplasms. Immunohistochemical stains are sometimes necessary to clarify the histogenesis of a lesion.


OBJECTIVE
To evaluate dermatofibromas for expression of desmin and smooth muscle myosin heavy chain (SM-MHC) antigens, which are commonly used as evidence of smooth muscle differentiation.


METHODS
We studied 100 consecutive cases of dermatofibroma using hematoxylin-eosin-stained sections and immunoperoxidase staining with antibodies against desmin, SM-MHC, and smooth muscle actin.


RESULTS
We found focal positivity for desmin in 9 cases, and in 2 of these cases, at least 10% of lesional cells showed strong expression. We found focal staining for SM-MHC in 10 cases, and in 2 of these cases, at least 10% of the lesional cells were positive. Regions positive for desmin and/or SM-MHC did not show definite histologic features of myogenous differentiation on hematoxylin-eosin-stained sections. All dermatofibromas expressing desmin and SM-MHC were also strongly positive for smooth muscle actin.


CONCLUSIONS
About 10% of dermatofibromas show focal expression of desmin and SM-MHC, and this expression may be present in up to 10% to 15% of lesional cells. Thus, in dermal spindle cell lesions, focal expression of these muscle antigens, like that of smooth muscle actin, is not diagnostic of a smooth muscle tumor.
Bruecks
Andrea K
AK
Department of Pathology and Laboratory Medicine, Calgary Laboratory Services, University of Calgary, Alberta, Canada. andrea.bruecks@cls.ab.ca
Trotter
Martin J
MJ
D000199:Actins / Q000378:metabolism; D000328:Adult; D000368:Aged; D002452:Cell Count; D003893:Desmin / Q000378:metabolism*; D005260:Female; D018219:Histiocytoma, Benign Fibrous / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007124:Immunoenzyme Techniques; D007889:Leiomyoma / Q000378:metabolism / Q000473:pathology; D008297:Male; D008875:Middle Aged; D018995:Myosin Heavy Chains / Q000378:metabolism*; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology; D024745:Smooth Muscle Myosins / Q000378:metabolism*
D000199:Actins; D003893:Desmin; D024745:Smooth Muscle Myosins; D018995:Myosin Heavy Chains