Prominent CD56 expression by damaged and regenerating muscle fibers in the skin.
BACKGROUND
Antibodies to CD56 label natural killer cells as well as tissues with neural and neuroendocrine differentiation. Despite its apparently limited distribution, other conditions may unexpectedly show strong CD56 expression.


METHODS
We report three cases to document another setting with strong expression of CD56 in the skin: damaged and/or regenerating muscle fibers. One case of cutaneous lupus erythematosus, one case of lymphomatoid granulomatosis, and one case of a dermal scar adjacent to cutaneous muscle fibers were evaluated with a panel of antibodies, including CD56.


RESULTS
All cases showed histopathologic evidence of muscle fiber damage in the setting of lymphocytic infiltration or trauma. All cases showed prominent expression of CD56 by damaged and/or regenerating muscle fibers. The degree of CD56 expression was directly proportional to the proximity to the injury site and inversely proportional to fiber diameter.


CONCLUSIONS
Even though CD56 is a useful marker for certain cytotoxic lymphomas and neural/neuroendocrine neoplasms, its expression is not limited to these conditions. Our cases highlight another unexpected example of strong CD56 expression in the skin: damaged and/or regenerating muscle fibers. The growing list of CD56-positive conditions suggests that this marker may not be as specific as initially assumed.
Department of Pathology, Yale University School of Medicine, New Haven, CT, USA.
Kristopher
K
McKay
Jennifer
J
McNiff
Antonio
A
Subtil
D000293:Adolescent; D000328:Adult; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000378:metabolism*; D019002:CD56 Antigen / Q000096:biosynthesis*; D002921:Cicatrix / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D008178:Lupus Erythematosus, Cutaneous / Q000378:metabolism* / Q000473:pathology; D008230:Lymphomatoid Granulomatosis / Q000378:metabolism* / Q000473:pathology; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000473:pathology; D009124:Muscle Proteins / Q000096:biosynthesis*; D012038:Regeneration; D012867:Skin / Q000293:injuries / Q000378:metabolism* / Q000473:pathology; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology
D014408:Biomarkers, Tumor; D019002:CD56 Antigen; D009124:Muscle Proteins; C522918:NCAM1 protein, human