Leflunomide-related acute interstitial pneumonia in two patients with rheumatoid arthritis: autopsy findings with a mosaic pattern of acute and organizing diffuse alveolar damage

We describe two cases of leflunomide-related interstitial pneumonia (IP). A 75-year-old woman with rheumatoid arthritis (RA) developed rapidly progressing IP 45 days after institution of leflunomide. She died of respiratory failure, and an autopsy revealed a mixed pattern of acute and organizing diffuse alveolar damage. A 69-year-old woman with RA also developed acute IP 3 months after institution of leflunomide. Methylprednisolone pulse therapy and cholestyramine ameliorated her IP. The implication of leflunomide in the pathogenesis of IP was suggested.