Hypersensitivity pneumonitis with computed tomography findings resembling alveolar hemorrhage: a case report

Background Hypersensitivity pneumonitis is an interstitial pneumonitis caused by inhalation of various antigens, with primary treatment involving antigen avoidance. Typical computed tomography (CT) findings include diffuse ground-glass opacities, mosaic attenuation, and ill-defined centrilobular nodules. However, ground-glass opacities can also be seen in numerous other diseases, including alveolar hemorrhage, a life-threatening complication of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis that requires prompt intervention. We present a case of granulomatosis with polyangiitis exhibiting features of hypersensitivity pneumonitis that resembled alveolar hemorrhage. Case presentation This report describes the case of an 80-year-old Japanese male with stable granulomatosis with polyangiitis who developed hypersensitivity pneumonitis. The patient presented with a fever and general fatigue. A chest CT scan revealed multiple ground-glass opacities and a halo sign, which are often observed in alveolar hemorrhage or alveolitis associated with ANCA-associated vasculitis. However, physical examination and laboratory findings did not indicate relapse of granulomatosis with polyangiitis. We promptly performed bronchoalveolar lavage and excluded alveolar hemorrhage. A detailed history-taking revealed that the patient had been exposed to birds for the preceding 3 months and the patient was diagnosed with bird-related hypersensitivity pneumonitis. Prompt bronchoalveolar lavage and thorough history-taking are essential for accurate differentiation between hypersensitivity pneumonitis and alveolar hemorrhages when these imaging characteristics are observed. Conclusions This case demonstrates that hypersensitivity pneumonitis can present with ground-glass opacities and CT halo sign resembling alveolar hemorrhage. Prompt bronchoalveolar lavage and thorough history-taking are essential for accurate differentiation, preventing unnecessary immunosuppressive therapy escalation and ensuring appropriate antigen avoidance treatment. Clinical trial number Not applicable.