Pulmonary Langerhans’ Cell Histiocytosis – Advances in the Understanding of a True Dendritic Cell Lung Disease

Abstract

Pulmonary Langerhans’ cell histiocytosis (PLCH) is a rare lung disease that generally, but not invariably, occurs in cigarette smokers. The pathologic hallmark of PLCH is expansion of Langerhans and other inflammatory cells in a bronchiolocentric fashion. The precise mechanisms by which smoking induces PLCH in susceptible individuals are not known, but likely involve a combination of molecular events resulting in enhanced recruitment and retention of Langerhans cells in small airways. PLCH is primarily a disease of small airways, with variable extension into the lung interstitial and vascular compartments. While cellular inflammation is evident early in the disease course, the more advanced stages are characterized by cystic lung destruction, cicatricial scarring of airways, pulmonary vascular remodeling, and emphysematous change. High resolution chest CT scanning is very useful in the diagnostic evaluation and may show nodular and cystic changes that are virtually pathognomonic. In several instances, lung biopsy (bronchoscopic or surgical) is necessary to establish a definitive diagnosis. All smokers with PLCH must be counseled on smoking cessation, while for selected patients, pharmacotherapy with corticosteroids or other agents may be indicated to prevent disease progression and preserve lung function. All symptomatic patients should be screened for the presence of pulmonary hypertension, which may respond to vasodilator therapy. The prognosis for a significant proportion of patients is relatively good, particularly if smoking cessation is achieved, and if longitudinal lung function testing shows stability. Pneumothoraces, secondary pulmonary hypertension, and the development of premature emphysema are important complications that shorten life expectancy. Lung transplantation may be indicated for patients with relentless progressive disease.