Pulmonary involvement with langerhans cell histiocytosis is characterized by a granulomatous infiltration of the alveolar septae and bronchial walls by foamy histiocytes. The disorder is uncommon, accounting for only 3.4% of cases of chronic diffuse interstitial lung disease. Patients with isolated pulmonary involvement are usually older (30-40y), Caucasian, and there is an equal
frequency in men and women (although young men appear to have the worst prognosis). The disorder is rare in blacks. There is a strong association with smoking (90-95% of cases occur in smokers) and symptoms often improve with cessation of smoking. About one-third of patients are asymptomatic. Symptomatic patients may present with cough (66%), weight loss, fever, diabetes insipidus (25%), or pneumothorax (15-25%). There is no consistent pulmonary function test finding, but airway obstruction is common. Treatment consists of chemotherapy. Remission occurs in about 30% of patients, stabilization in 30%, and progression in 30%. Scuba diving is contraindicated.
CXR: On CXR there is usually diffuse reticulonodularity (3-10 mm nodules which may cavitate) in a symmetric upper lobe predominance (bases tend to be spared) with preservation of lung volumes. Associated pneumothorax is found in 15-25% of cases. Pleural effusion is rare.
Computed tomography: On HRCT the distribution of the disease is similar to that on CXR with an upper lobe predominance. Findings include centrilobular opacities, cystic cavitation of small nodules, and cysts. The cysts are usually less than 10 mm in size, although cysts larger than 10 mm are found in over half the cases. The walls of the cysts are usually thin, but can be variable, and the cysts are not necessarily round (they may be bilobed or branching). The intervening lung parenchyma appears normal. In the late stage, there may be diffuse cysts, with no nodules evident, while in the early stages, only nodules may be seen. Mediastinal adenopathy has been described in some series, but is usually uncommon.
The dangers of ‘burst lung’ from barotrauma are great for scuba diving and possibly from air travel. Arterial gas embolism from pulmonary barotrauma should be treated immediately by recompression ina chamber.