fibrosing alveolitis /fī″brōsing/ [L, fibra + alviolus, small hollow; Gk, itis, inflammation] , a severe form of alveolitis characterized by dyspnea and hypoxia. It occurs in advanced rheumatoid arthritis and other autoimmune diseases. X-ray films show thickening of the alveolar septa and diffuse pulmonary infiltrates. See also alveolitis.