Pulmonary LCH is more prevalent in smokers than in nonsmokers and the male/female ratio may be near unity depending on the incidence of smoking in the population studied.[7,8] Patients with pulmonary LCH usually present with a dry cough, dyspnea, or chest pain, although nearly 20% of adults with lung involvement have no symptoms.[9,10] Chest pain may indicate a spontaneous pneumothorax (10%–20% of adult pulmonary LCH cases). The LCH cells in adult lung lesions were shown to be mature dendritic cells expressing high levels of the accessory molecules CD80 and CD86, unlike Langerhans cells (LCs) found in other lung disorders. In addition, pulmonary LCH in adults appears to be primarily a reactive process, rather than a clonal proliferation as seen in childhood LCH.
The course of pulmonary LCH in adults is variable and unpredictable. Fifty-nine percent of patients do well with either spontaneous remission with cessation of smoking, or with some form of therapy. Adults with pulmonary LCH who have minimal symptoms have a good prognosis, although some have steady deterioration over many years. Age older than 26 years and lower FEV1/FVC ratio and higher RV/TLC ratio are adverse prognostic variables. About 10% to 20% have early severe progression to respiratory failure, severe pulmonary hypertension, and cor pulmonale. Adults who have progression with diffuse bullae formation, multiple pneumothoraces, and fibrosis have a poor prognosis.[14,15] The remainder have a variable course with stable disease in some patients and relapses and progression of respiratory dysfunction in others, some after many years. One study reported that smoking cessation did not increase the longevity of pulmonary LCH patients, apparently because the tempo of disease is so variable. Patients receiving lung transplantation for treatment of pulmonary LCH have a 77% survival rate at 1 year and 54% survival rate at 10 years, with a 20% chance of LCH recurrence.
The most frequent pulmonary function abnormality finding in patients with pulmonary LCH is a reduced carbon monoxide diffusing capacity in 70% to 90% of cases.[13,18] A high-resolution computed tomography (CT) scan, which reveals a reticulonodular pattern classically with cysts and nodules, usually in the upper lobes and sparing the costophrenic angle, is characteristic of LCH. Despite the typical CT findings, most pulmonologists agree that a lung biopsy is needed to confirm the diagnosis. The presence of cystic abnormalities on high-resolution CT scans appears to be a poor predictor of which patients will have progressive disease. A study correlating lung CT findings and lung biopsy results in 27 pulmonary LCH patients has shed some light on pulmonary LCH. Thin-walled and bizarre cysts had active LCs and eosinophils. Fifty-two percent of patients improved, most with smoking cessation, and some with steroid treatment within 14 months of diagnosis. Four patients (15%) were stable, and nine (33%) progressed over 22 months.