Erdheim-Chester disease: an unusual presentation of an uncommon disease.

Erdheim-Chester disease (ECD) is a rare, non-Langerhans cell histiocytosis with classic radiographic findings of patchy or diffuse osteosclerosis predominantly involving the long bones in a bilaterally symmetrical pattern. A 49-year-old woman presented with diffuse lymphadenopathy, painful skin lesions, and constitutional symptoms. Recent history was significant for a nontraumatic fracture of the tibia 3 weeks prior to admission. Physical examination and laboratory studies were notable for lower extremity pain and swelling, nodular lesions on the skin, and normocytic, normochromic anemia. Plain radiographs showed a lytic pattern of destruction with a superimposed fracture in the left proximal tibia. MRI showed focal bone marrow replacement extending from the subchondral bone to the tibial diaphysis. Excisional lymph node and skin biopsies of the lesions demonstrated a CD-68 positive, S-100 variable, and CD1a-negative histiocytic cell proliferation filling the dermis and completely replacing the sampled lymph node with an accompanying chronic inflammatory infiltrate and fibrosis, pathognomonic for ECD. We report an unusual case of ECD presenting initially as diffuse, painful lymphadenopathy, and subsequently demonstrating a lytic lesion of the tibia underlying a nontraumatic fracture.