Abstract: Intravascular large B-cell lymphoma(IVLBCL) is a rare and aggressive type of lymphoma with diverse and nonspecific clinical manifestations, often leading to misdiagnosis. This article reports a case of IVLBCL in a middle-aged male patient who initially presented with pulmonary arterial hypertension(PAH). The patient exhibited progressive hypoxemia and PAH, showing poor response to standard PAH therapy. Laboratory tests indicated a hyperinflammatory state and significantly elevated lactate dehydrogenase levels, while imaging revealed diffuse bilateral lung lesions. Random skin biopsy identified atypical B lymphocytes within subcutaneous capillaries, confirming the diagnosis of IVLBCL. Following treatment with the ZR-CHOP regimen, the patient's symptoms and laboratory parameters improved markedly. By reviewing relevant literature, this article systematically outlines the diagnostic and therapeutic process of this case, aiming to provide insights for the clinical recognition of such rare presentations.