A 68 year-old woman presented with a 15 day history of a solitary asymptomatic nodule on the forearm. She suffered from multiple myeloma (MM) IgG.
The histological examination of the skin lesion showed a diffuse dermal infiltrate (Fig. 2) composed of atypical, monomorphous, medium size cells, with prominent nucleolus, arranged in nests and narrow cords. Numerous mitosis were detectable (Fig. 3).
Immunohistochemical staining was positive for CD138, while it was negative for CD79a, CD20 and CD45 in the cells forming the dermal infiltrate.Additional immunohistochemical stains for immunoglobulin light chain lambda and kappa showed a restriction for lambda light chain in the cells forming the dermal infiltrate (Fig. 4 A, B).