A clinicopathologic and immunohistochemical comparative study of cutaneous and intramuscular forms of juvenile xanthogranuloma.

The clinical, histopathologic, and immunohistochemical features of 18 cases of cutaneous juvenile xanthogranuloma (JXG) and two cases of intramuscular JXG were compared. Clinically, intramuscular JXG differs from cutaneous JXG in that it seems to affect exclusively infants and toddlers and to occur as solitary lesions in skeletal muscles of the trunk rather than in the head and neck region, the most common location of cutaneous JXG. Also, the lesions of intramuscular JXG, unlike those of cutaneous JXG, tend to be composed of a monotonous population of histiocytelike cells, with rare, if any, foamy macrophages or Touton-type multinucleated giant cells. These atypical histopathologic features together with infiltrating borders and the presence of a few mitotic figures are the main reason for the misdiagnosis of intramuscular JXG. Awareness of this atypical presentation should prevent misinterpretation of childhood sarcomas and lymphoproliferative disorders. Immunohistochemically, the cutaneous and intramuscular lesions of JXG exhibit identical profiles, and PG-M1 is the best immunohistochemical marker of JXG. Most likely, JXG is a pathologic histiocytic proliferation of a benign nature that should be treated conservatively. The present study failed to demonstrate any myofibroblastic participation in JXG. Its cause is obscure, and although the hypothesis of viral infection seems attractive considering the clinical picture of the lesion, the present study failed to demonstrate any association between JXG and Epstein-Barr virus, varicella-zoster virus, or cytomegalovirus infection.