Langerhans' cell histiocytosis of the lung, PLCH

Definition

A form of interstitial lung disease due to the proliferation of Langerhans' cells. Isolated pulmonary disease is probably non-neoplastic3, in contrast to most extra-pulmonary Langerhans cell proliferations.

Epidemiology

Most cases of isolated Langerhans' cell histiocytosis of the lung occur in adults, of whom over 95% are smokers or ex-smokers3. 15% of adult cases have extrapulmonary disease: pulmonary involvement with systemic Langerhans' cell histiocytosis occurs more often in children. The mean age of pulmonary adult cases is forty years. There may be an increased risk of developing other malignancies2.

Clinical features

A minority of patients are asymptomatic. Symptoms consist of cough, dyspnea, chest pain, malaise, weight loss and fever. Most patients have abnormal pulmonary function tests, which may be restrictive, obstructive or a deficit in diffusion capacity. Pulmonary function tests show reduced gas exchange4.

Radiology

Disease is predominantly of upper and mid zones2, with sparing of the costophrenic angles, consisting of (micro)nodules with cystic change2,3. This is sometimes accompanied by ground glass change4. Honeycomb fibrosis is rare3.

Histopathology

Most patients, being smokers, also have emphysema and respiratory bronchiolitis. The lesions of PLCH consist of cellular stellate proliferations of Langerhans' cells and eosinophils around small airways. They progress from cellular to fibrotic, eventually being devoid of recognizable Langerhans' cells. Langerhans' cells have pale eosinophilic cytoplasm and delicately folded nuclear membranes.

Immunohistochemistry

	S-100	positive, 10/107
	CD1a	16/175, 24/246, 10/107
	Langerin	17/175, 24/246, 10/107

See immunohistochemistry of systemic Langerhans' cell histiocytosis.

Ultrastructure

Birbeck granules are characteristic of Langerhans' cells.

Differential diagnosis

Erdheim-Chester disease: the infiltrate has a more lymphatic distribution; the histiocytes are negative for S-100.

Management

Smoking cessation and steroids2.

Prognosis

15% to 33% of patients show progressive disease; progression may be slow. The five year survival is 75%, the ten year survival is 65% and the median survival is 12.5 years2.