Pulmonary intravascular large B-cell lymphoma misdiagnosed as allergic pneumonia: a case report and literature review.

Pulmonary intravascular large B-cell lymphoma (PIVLBCL) is an extremely rare subtype of extranodal diffuse large B-cell lymphoma (DLBCL). This hematologic malignancy exhibits nonspecific radiological features, including ground glass opacities (GGOs), often leading to misdiagnosis as interstitial lung disease (ILD). We present a 51-year-old female hairdresser with progressive dyspnea and 20 years of occupational hair dye exposure. Initially, she was misdiagnosed with chronic bronchitis due to a persistent dry cough. Then her initial chest CT demonstrated diffuse bilateral GGOs with isolated diffusion capacity of the lungs for carbon monoxide (DLCO) reduction (46.1% predicted) and normal spirometry, which led to a second misdiagnosis as hypersensitivity pneumonitis (HP). Despite initial improvement with corticosteroids, respiratory deterioration occurred during tapering. Finally, transbronchial lung cryobiopsy (TBCB) confirmed PIVLBCL, showing intravascular lymphoid proliferation (CD20+/BCL-6+/Ki-67≈80%). The R-CHOP chemotherapy treatment led to a complete remission for her, and the DLCO improved to 68% of the predicted value at the 6-month follow-up. A literature review of 75 PIVLBCL patients revealed that fever (74.7%) and dyspnea (65.3%) were the predominant presentations. GGOs were observed in 54.7% of cases, with frequent misdiagnosis as ILD (31.8%) or pneumonia (31.8%). TBCB provided definitive diagnostic evidence, demonstrating its clinical utility in resolving ambiguous pulmonary opacities. Clinicians should maintain high suspicion for PIVLBCL when encountering diffuse GGOs with isolated DLCO reduction, even without classic risk factors.