this is a multicenter retrospective study on patients with pulmonary LCH who were sequentially evaluated by concomitant lung HRCT and lung function testing. The objectives of this study were: 1) to determine the changes over time of lung function parameters in patients with pulmonary LCH; 2) to compare the variations of HRCT and lung function results during follow-up; 3) to address the respective interest of these investigations for identifying the patients who eventually will experience a progression of their disease.

Pulmonary Langerhans cell histiocytosis (pulmonary LCH) is an uncommon disorder, characterized by the accumulation of CD1a+ Langerhans cells (LCs) organized in granulomas that develop in, and destroy the wall of distal bronchioles. In adults the disease occurs predominantly in young smokers from both genders, with a peak incidence at 20-40 yrs of age, although female may be slightly older. High resolution computed tomography (HRCT) of the lung has provided a considerable input for the diagnosis of pulmonary LCH.

We conducted a multicenter retrospective study on patients with pulmonary LCH who were sequentially evaluated by concomitant lung HRCT and lung function testing. The objectives of this study were: 1) to determine the changes over time of lung function parameters in patients with pulmonary LCH; 2) to compare the variations of HRCT and lung function results during follow-up; 3) to address the respective interest of these investigations for identifying the patients who eventually will experience a progression of their disease. Results of this study may help to improve the management of patients with adult pulmonary LCH.

Inclusion Criteria:

• pulmonary HLP diagnosed between June 1989 and February 2005

Exclusion Criteria:

• followed up for less than 6 months
• with less than 2 lung HRCT and lung function tests at the same time or within a 2 month period

• Patients with pulmonary LCH
• enrolled in eight teaching hospitals
• evaluated between June 1989 and February 2005