A skin biopsy may be performed, both for diagnosis and cosmesis. The specimen usually consists of a complete excision of the papule or nodule. Early biopsy specimens reveal a dense monomorphous histiocytic infiltrate in the dermis. Extension into subcutaneous tissue, fascia, and muscle occurs in approximately one 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 irregular dense bodies. Clustered comma-shaped bodies occasionally are observed on electron microscopy but are not specific. Use of special stains is important to differentiate JXG from Langerhans and non Langerhans cell histiocytoses. HAM56, HHF35, KP1, KiM1P, and Vimentin and are negative to CD1 and S100. Anticipatory care, with patient reassurance, is appropriate because of the self-limiting benign nature of the lesions.