Introduction

Langerhans cell histiocytosis (LCH) encompasses a group of disorders of unknown origin with diverse clinical presentations and outcomes, characterized by infiltration of involved tissues by pathologic Langerhans cells (LCs). Acute disseminated LCH is a severe multisystem disease that predominantly affects young children. Multifocal LCH is seen mainly in older children and adolescents and runs a variable but usually more favorable course. Single-system disease (eosinophilic granuloma) is characterized by involvement of a single organ (bone, lungs, or skin) and often follows a benign course (Howarth et al., 1999). Pulmonary involvement in patients with multisystem disease is rarely at the forefront of the clinical picture. Isolated or predominant pulmonary involvement is the pattern encountered by pulmonologists in adults and has a number of specific epidemiological and clinical features that warrant its individualization as a separate entity (Tazi et al., 2000; Vassallo et al., 2000; Sundar et al., 2003).

Epidemiology

Adult lung LCH is an uncommon disorder that occurs almost exclusively in smokers. In an early series of more than 500 patients with diffuse infiltrating lung disease, surgical lung biopsy showed LCH in less than 5% of cases (Gaensler and Carrington, 1980). Several studies have documented comparable data thereafter as reviewed in Tazi et al. (2000) and Vassallo et al. (2000). The prevalence of pulmonary LCH (pLCH) is, however, probably underestimated because some patients are asymptomatic or experience spontaneous remission, and histological findings are nonspecific in advanced forms. The wide use of chest high-resolution computed tomography (HRCT) in the evaluation of patients may increase the number of patients in whom pLCH is diagnosed.