Introduction

In 1953, Lichtenstein coined the term histiocytosis X for the different forms of Langerhans cell histiocytosis (LCH), the X denoting his uncertainty about the disease and its pathogenesis (Lichtenstein, 1953). Fifty years later some of the uncertainty still exists. The histopathological appearance of the various forms of ‘LCH’ is identical, yet the intriguing question remains. How is it that patients with such a variable clinical profile, from a single self-healing bone lesion to a generalized disorder resistant to any known therapy, seem to have the same disease? Many more pieces of the ‘LCH jigsaw puzzle’ are still missing and need to be fitted in. Mean while, descriptions of the clinical features, the natural history of the disease and the long-term outcome provide a useful framework for clinicians, for recognition and management of the disease. In describing the clinical picture of LCH, we have focused on those few studies which have included more than 50 patients (Table 6.1). It is noteworthy that until April 2004, only 14 studies, the product of just 10 centres or cooperative groups, have reported on more than 100 patients.

Clinical involvement by specific organs

The frequency of involvement of specific organs or ‘organ systems’ is described in the following sections in descending order of frequency. Most cooperative studies record specific system involvement at diagnosis; in some cases, events during the course of LCH are also included.

Bone

In most surveys, bone lesions are present in around 80% of patients.