A skin biopsy may be performed, both for diagnosis and cosmesis. This will usually consist of complete excision of the papule or nodule. Early biopsies reveal a dense monomorphous histiocytic infiltrate in the dermis. Extension into subcutaneous tissue, fascia, and muscle occurs in approximately a third of cases. Older lesions contain foam cells, Touton giant cells, and foreign body giant cells.
Old lesions demonstrate fibrosis.
The histiocytes contain pleomorphic nuclei and contain irregular dense bodies. Clustered comma-shaped bodies occasionally are observed on electron microscopy, but are not specific. Performing special stains is important to differentiate JXG from Langerhans and non-Langerhans cell histiocytoses. In JXG, the histiocytes are HAM56, HHF35, KP1, KiM1P, and Vimentin positive, and CD1 and S100 negative. Because of the self-limiting, benign nature of the lesions, anticipatory care with reassurance is appropriate.