Stages of interstitial pneumonitis in rheumatoid arthritis. Left panel: The histopathologic finding of permeation of the interaveolar septae by a lymphocytic infiltrate is consistent with lymphocytic interstitial pneumonitis in rheumatoid arthritis. Right panel: A more advanced stage of lymphocytic interstitial pneumonitis reveals germinal center formation and a focus of angiocentric granulomatous inflammation.
