Rare diseases bullet 9: Adult pulmonary Langerhans' cell histiocytosis

In the early 1950s Lichtenstein introduced the term histiocytosis X to describe a group of syndromes with seemingly unrelated clinical features, but whose pathological findings were characterised by the infiltration of involved tissues with large numbers of unusual histiocytes, often organised as granulomas.1 Subsequently it was shown that these histiocytes were similar to Langerhans' cells normally present in the skin and other epithelia, a finding that led to the current designation of Langerhans' cell histiocytosis (LCH) for this group of disorders.2 3 Although the different forms of LCH are united by a common histopathological finding—the Langerhans' cell granuloma—the clinical spectrum of these disorders is extremely large, extending from an acute disseminated form which usually occurs in infants and carries a poor prognosis, to the presence of lesions localised to a single tissue which follows a more benign clinical course (table1).4-8 Pulmonary involvement is not unusual in systemic forms of LCH.4-8 In this setting prognosis depends on the age of the patients, the number of organs involved, and the extent to which normal function is impaired.4-9 Pulmonary symptoms are rarely prominent, although the presence or absence of lung involvement does appear to have a bearing on the outcome.7 9 The lung can also be the predominant or only site involved in LCH.4-6 8 10 Localised pulmonary LCH, the form most frequently encountered by specialists in pulmonary medicine, occurs most commonly in young adults and has several unique clinical and epidemiological features that justify its classification as a distinct clinicopathological entity.4 6 8 11-17The development of high resolution computed tomographic (HRCT) scanning has proved to be of considerable help in the diagnosis of this disorder.18 19 In contrast, the natural history of localised pulmonary LCH remains poorly defined and no …