Bone is the commonest single organ involved in Langerhans cell histiocytosis (LCH) in children. Of 154 consecutive children admitted to a single large institution, 126 (81%) had bone involvement, of whom 80% had single system (SS) disease and 20% bone disease as part of multisystem (MS) LCH. A single bone was involved in 76% – unifocal bone (UFB) and two or more bones – multifocal bone (MFB) in 24% (Stuurman et al., 2003), correlating almost exactly with the 78% UFB and 22% MFB found by the DAL-HX group (Titgemeyer et al., 2001).

The commonest presentation of LCH in children is thus with UFB. The picture is different in adults in whom SS skin and lung disease predominate, and in whom bone is more often part of MS disease (Malpas, 1998; Aricò et al., 1999, 2003).

Clinical aspects

The bones most commonly involved are skull, spine, lower extremity, pelvis, ribs and upper extremity (Table 8.1). Proximal long bones are commoner than distal (Figure 8.1) (Egeler et al., 1999), and hands and feet are rarely involved. In adults the flat bones are involved more frequently, with jaw involved in 30% (Baumgartner et al., 1997). The ribs accounted for only 6% of lesions in Baumgartner's series but was the second commonest bone affected in two other adult series (Kilpatrick et al., 1995; Islinger et al., 2000) (Figure 8.2). In the long bones diaphysis and metaphysis are equally involved, epiphysis is commonly spared, but epiphyseal location does not exclude LCH (Ghanem et al., 2003).