Intravascular lymphoma mimicking hypersensitivity pneumonitis: A case report.

Intravascular large B-cell lymphoma (IVLBCL) is a rare and often fatal malignancy that presents with non-specific pulmonary symptoms and abnormal imaging findings. We report a unique case of IVLBCL in a 73-year-old man who initially presented with fever and bilateral ground-glass opacities on computed tomography that mimicked hypersensitivity pneumonitis. The symptoms temporarily improved with environmental antigen avoidance, which delayed a correct diagnosis. Ultimately, transbronchial lung cryobiopsy confirmed IVLBCL, and chemotherapy was effective. This case highlights the potential for spontaneous regression of IVLBCL and the importance of considering malignancy when clinical improvement is not sustained.