Diagnosis: Fibroblastic focus
• Fibroblastic foci are seen at the interface of spared and fibrotic lung. They can be plentiful, although in most cases they are not. They are thought to be the active component of the progressive lung fibrosis of usual interstitial pneumonia, which is clinically idiopathic pulmonary fibrosis.
• The paucity of inflammation is typical of usual interstitial pneumonia (UIP)/idiopathic pulmonary fibrosis (IPF). This disease does not appear to respond to steroid therapy, and it is likely that complications of steroid therapy outweigh the benefit in these cases. Given the absence of effective therapy, progression to end-stage fibrosis occurs in most patients, leading to a high rate of organ failure requiring transplantation or to death.
• Fibroblastic proliferations can occur in other interstitial lung disease. It is the location/distribution and number of fibroblastic foci, in conjunction with the absence of inflammation, organizing pneumonia, and granulomas that make the diagnosis of UIP.
• Endstage or honeycomb lung is the endpoint of lung fibrosis. In these areas, fibroblastic foci may not be seen.
• Usual interstitial pneumonia can be part of an idiopathic process, but can be seen in connective tissue disease, some medication reactions, and extrinsic allergic alveolitis. Asbestos exposure can lead to lung fibrosis. Lung fibrosis can also occur in Hermansky-Pudlak syndrome, dyskeratosis congenita, and certain surfactant deficiencies. In these syndromes patients are usually younger than in idiopathic cases with usual interstitial pneumonia pattern.
