(See also Overview of Idiopathic Interstitial Pneumonias.)
Langerhans cell histiocytosis can affect other organs (such as the pituitary gland, bones, and the lymph nodes) as well as the lungs. The cause is unknown, and the disorder is rare. It occurs almost exclusively in whites aged 20 to 40 who smoke cigarettes. Pulmonary Langerhans cell histiocytosis starts with infiltration of the lung by histiocytes, which are cells that scavenge for foreign materials, and to a lesser extent by eosinophils, which are cells that are normally involved in allergic reactions.
About 15% of people have no symptoms and the disorder is first recognized when an imaging study of the chest is done for another reason. The remainder develop coughing, shortness of breath, fever, chest pain worsened by deep breathing, fatigue, and weight loss. Pneumothorax (a collapsed lung) is a common complication due to rupture of a lung cyst. It occurs in 10 to 25% of people with pulmonary Langerhans cell histiocytosis and may be the cause of the first symptoms that develop. Scarring makes the lungs stiff and impairs their ability to transfer oxygen into and out of the blood. A few people cough up blood (hemoptysis).
Some people have pain in certain parts of a bone or a pathologic bone fracture (a fracture that occurs after only a minor injury because the bone has been thinned by a disorder). A few people develop central diabetes insipidus when histiocytes also affect the pituitary gland in the brain. The person makes excessive amounts of urine that is dilute. People with central diabetes insipidus probably have a worse prognosis than those who do not.
Chest x-rays show nodules, small thick-walled lung cysts, and other changes that are typical of pulmonary Langerhans cell histiocytosis. Computed tomography (CT) may show these changes in enough detail to establish the diagnosis. Pulmonary function testing shows that the amount of air the lungs can hold is below normal.
If CT does not establish the diagnosis, biopsy is required.
X-rays of bones may show that they are also affected.
Half of people are alive more than 12 years after diagnosis. Death usually results from respiratory failure or cor pulmonale. People with pulmonary Langerhans cell histiocytosis should stop smoking. When people stop smoking, improvement occurs in about one third of cases.
Pulmonary Langerhans cell histiocytosis may be treated with corticosteroids and/or immunosuppressants, such as cyclophosphamide, although no therapy is clearly beneficial.