The Fibrosing Process in “Accelerated Pulmonary Fibrosis” (So-called Hamman-Rich Syndrome)
Hamman-Rich syndrome is characterized by sudden onset of respiratory symptoms, a fulminant course with death occurring within several months of onset, histological evidence of pulmonary fibrosis, and an unknown etiology. Katzenstein et al recently proposed that the term "acute interstitial pneumonia (AIP)" be applied to this syndrome. We collected 11 autopsy cases meeting the clinical criteria for AIP. Using histopathological criteria, and examining changes in epithelial cells and basement membranes detectable in these cases by immuno-histochemical technique, we distinguished the four patterns of fibrosis defined in our previous study; that is, intraluminal membranous, intraluminal polypoid, intraluminal diffuse and interstitial fibrosis. In the majority of cases, the three patterns of intraluminal fibrosis, each of which showed anatomic connection with the original alveolar framework only at the alveolar duct walls, predominated, while interstitial fibrosis was a rare and minor component. Alveolar epithelia and basement membranes were well-preserved along the alveolar walls, but not on the alveolar duct walls, into which fibroblasts appeared to have migrated and formed fibrous tissue within the alveolar spaces. In a few cases, intraluminal diffuse fibrosis alone predominated in every portion of the lung, and a diagnosis of paraquat intoxication could not be excluded with certainty. Our observations suggest that the term "accelerated pulmonary fibrosis" rather than acute interstitial pneumonia would be a more appropriate designation for such lesions, since the fibrotic process involved is not acute but is accelerated, and because disease-associated fibrotic tissue is present in the intraluminal spaces rather than in the interstitium.