Pulmonary langerhans cell histiocytosis
 Discussion of Pulmonary langerhans cell histiocytosis
- Langerhans cell histiocytosis (LCH) was formerly known by as histiocytosis X and eosinophilic granuloma.
- Although the etiology of LCH is unknown, theories include viral infection, antigen exposure, and somatic mutation.
- Pulmonary LCH refers to LCH isolated to the respiratory system (notably the lungs).
- Found almost exclusively in cigarette smokers.
- Presents in the third to fourth decade of life.
- Most common clinical symptoms include dyspnea, cough, and fatigue.
- Decrease in carbon monoxide diffusing capacity is present in up to 90% of patients.
- For most patients, symptom stabilization occurs with smoking cessation alone.
- Corticosteroid therapy caused disease stabilization in some studies.
- Patients with pulmonary LCH have variable and uncertain clinical courses.
- Adults with the disease have decreased overall long-term survival compared to those without the disease.
- Mortality from pulmonary LCH can occur due to pulmonary hypertension or respiratory failure.
- There is no known link between relapse of disease and continuation of smoking or between regression of disease and cessation of smoking.
 Imaging Findings for Pulmonary langerhans cell histiocytosis
- Radiologic findings of pulmonary LCH vary depending on the stage of the disease at diagnosis.
- Middle and upper lung zones are involved to a greater extent than the lung bases.
- Diffuse bilateral ill-defined nodules will be seen in early stages. It is thought that these nodules undergo cystic degeneration as the disease progresses, and so a reticular pattern begins to predominate on chest radiographs as the numerous cystic walls are superimposed on one another.
- The cysts and residual parenchyma can undergo fibrosis over time and eventually lead to changes of honeycombing.
- Diagnosis can be easily made with high-resolution CT by showing both ill-defined nodules and cysts in a heavy smoker.
- Diagnostic accuracy of high-resolution CT falls short when only nodules or cysts alone are present.
- Differential diagnosis of primarily cystic lung disease includes predominantly cystic pulmonary LCH, lymphangiomyomatosis, emphysema, and bronchiectasis.
- Cysts in LCH are often variable in size and wall thickness.
- Cysts of lymphangiomyomatosis can resemble those of pulmonary LCH, but they occur diffusely throughout the lungs and affect women almost exclusively.
- Cystic cavities of emphysema represent foci of destroyed parenchyma and lack definable walls.
- Cystlike bronchial dilatation seen in bronchiectasis can be distinguished by the communicating branching pattern seen on contiguous CT images.
 See Also
 External Links
 References for Pulmonary langerhans cell histiocytosis
- Danny L. Leatherwood, Darel E. Heitkamp, and Robert E. Emerson. Best Cases from the AFIP: Pulmonary Langerhans Cell Histiocytosis. RadioGraphics 2007 27: 265-268.