Organizing pneumonia (OP) is considered a non-specific repair process in lungs in response to various kinds of lung insults:
cryptogenic organizing pneumonia (COP) when the cause is not known
secondary organizing pneumonia when the cause is known
infection, inflammatory bowel disease, drugs (as in the above case), collagen vascular disease, organ transplantation and radiation direct to the chest
The histological hallmark of OP is intra-alveolar granulation tissue plugs (Masson bodies) which extend into bronchiolar lumina. The presence of these plugs is a prerequisite for restoration of tissue integrity.
Not to be confused with Bronchiolitis Obliterans Organizing Pneumonia (BOOP), which is a disease specifically of small airways.