Thoracic Oncology NetWork Online Puzzler - March 2009

Diagnoses and Discussion

Diagnosis: Radiation-induced bronchiolitis obliterans with organizing pneumonia (BOOP)

Radiation represents one of the key modalities of lung cancer management. It is employed with curative intent when patients cannot undergo surgical resection and employed with palliative intent to manage focal symptomatic metastases (ie, pain from a bone metastasis or malignant airway obstruction). This modality is associated with a number of potential complications. Radiation pneumonitis and radiation fibrosis are the most common adverse sequelae, and they may occur any time the lung lies within the radiation field. The risk of radiation pneumonitis is proportional to the volume of lung receiving radiation, the dose of radiation, as well as the presence or absence of concurrent chemotherapy. Clinical findings often manifest 6 weeks to 6 months after radiation begins and may include coughing, fevers, chest pain (sometimes pleuritic), and dyspnea. Chest radiographs may be normal, or they may manifest dense alveolar infiltrates within the radiation field, often with a sharp line separating the radiation field from surrounding normal lung that does not conform to anatomic barriers, such as pleura (straight-line sign).

Radiation-induced bronchiolitis obliterans with organizing pneumonia (BOOP), a more rare complication of radiation, was first reported in the 1990s among breast cancer patients.¹ It may occur 5 to 10 months after radiation therapy, its time course overlapping that of radiation pneumonitis. Radiation-induced BOOP is distinguished from cryptogenic organizing pneumonia (COP) by the fact that COP is idiopathic by definition. However, the pathologic findings of BOOP and COP are indistinguishable; organizing pneumonia is typically shown with prominent lymphocytes and plasma cells. Intraluminal polypoid plugs of connective tissue may or not be present. Chronic fibrotic changes, such as honeycombing on CT scans, are unusual. Symptoms and signs are similar to those of radiation pneumonitis, including cough, crackles, and fever. Unlike radiation pneumonitis, pulmonary infiltrates are not limited to the radiation field. Infiltrates are usually patchy and alveolar, often with air bronchograms, such as in the example here. They may be diffuse or nodular in extent. Transbronchial biopsy specimens rarely obtain sufficient tissue to confirm BOOP; therefore, the diagnosis rests on excluding other possibilities and/or surgical lung biopsy. The treatment of choice is systemic steroids.

This case represents radiation-induced BOOP subsequent to radiation the patient received for bone metastasis.

References:

1. Bayle JY, Nesme P, Bejui-Thivolet F, et al. Migratory organizing pneumonitis “primed” by radiation therapy. Eur Respir J 1995; 8:322-326

Puzzler Case Report submitted by:
Marc B. Feinstein, MD, FCCP
Member of the Thoracic Oncology NetWork Steering Committee