Hypersensitivity pneumonitis mimicked deadly lung bleeding on CT scans in one patient

An 80-year-old Japanese man with stable granulomatosis with polyangiitis developed a fever and general fatigue, and a chest CT scan revealed multiple ground-glass opacities and a halo sign. Those imaging features are often seen in alveolar hemorrhage, a life-threatening complication of ANCA-associated vasculitis that requires prompt intervention, and they raised immediate concern that his underlying vasculitis had relapsed. Instead, as reported in a case study published in BMC Pulmonary Medicine, the cause turned out to be bird-related hypersensitivity pneumonitis, an entirely different condition with a different treatment path.

Hypersensitivity pneumonitis is an interstitial pneumonitis caused by inhalation of various antigens, and its primary treatment is antigen avoidance. Typical CT findings include diffuse ground-glass opacities, mosaic attenuation, and ill-defined centrilobular nodules. The diagnostic difficulty in this case arose because ground-glass opacities can also appear in numerous other diseases, including alveolar hemorrhage. In a patient with a history of granulomatosis with polyangiitis, the same pattern could plausibly signal alveolar hemorrhage or alveolitis associated with ANCA-associated vasculitis, either of which would normally prompt escalation of immunosuppressive therapy.

The diagnostic workup depended on two steps taken in close succession. Physical examination and laboratory findings did not indicate relapse of the patient’s granulomatosis with polyangiitis, so the team promptly performed bronchoalveolar lavage and excluded alveolar hemorrhage. A detailed history-taking then revealed that the patient had been exposed to birds for the preceding three months, which led to the diagnosis of bird-related hypersensitivity pneumonitis. That exposure history had not been apparent until clinicians deliberately pursued it, underscoring how easily an environmental antigen can be overlooked when a patient’s medical record points toward a known autoimmune disease.

The authors conclude that this case demonstrates hypersensitivity pneumonitis can present with ground-glass opacities and a CT halo sign resembling alveolar hemorrhage. They emphasize that prompt bronchoalveolar lavage and thorough history-taking are essential for accurate differentiation between the two conditions when these imaging characteristics are observed, preventing unnecessary immunosuppressive therapy escalation and ensuring appropriate antigen avoidance treatment. In practical terms, the sequence matters: ruling out hemorrhage quickly through lavage, then reconstructing the exposure timeline through careful questioning, allowed the correct diagnosis without exposing the patient to intensified immunosuppression intended for a vasculitis relapse that was not occurring.

As a single-case report, the findings describe one patient’s experience rather than a systematic comparison of diagnostic strategies, and they cannot establish how often hypersensitivity pneumonitis produces this hemorrhage-like CT pattern more broadly. The report was published as an open-access article in BMC Pulmonary Medicine on 28 October 2026 by Hayato Shimizu and Hiroaki Nishioka, and it appears in a version shared early to provide faster access to peer-reviewed, accepted research, subject to further edits before the final Version of Record. Even with those limits, the case offers a concrete reminder for clinicians managing patients with known ANCA-associated vasculitis: a familiar imaging pattern does not guarantee a familiar diagnosis, and the fastest route to the right answer may combine an invasive but decisive procedure with the oldest diagnostic tool available, a detailed history.

Subject of Research: Hypersensitivity pneumonitis with CT findings resembling alveolar hemorrhage in a patient with granulomatosis with polyangiitis

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

Article References: Shimizu, H., & Nishioka, H. (2026). Hypersensitivity pneumonitis with computed tomography findings resembling alveolar hemorrhage: a case report. BMC Pulmonary Medicine. https://doi.org/10.1186/s12890-026-04886-9

Image Credits: AI Generated

DOI: 10.1186/s12890-026-04886-9

Keywords: hypersensitivity pneumonitis, alveolar hemorrhage, granulomatosis with polyangiitis, ANCA-associated vasculitis, ground-glass opacities, CT halo sign, bronchoalveolar lavage, bird exposure, case report, BMC Pulmonary Medicine, antigen avoidance, interstitial lung disease