Intravascular large B-cell lymphoma (IVLBCL): Subtle Presentation and Challenging Diagnosis

Intravascular large B-cell lymphoma (IVLBCL) is a rare, clinically aggressive lymphoma defined by the proliferation of atypical lymphoma cells in the lumen of all sized blood vessels, particularly capillaries. The reasons for this unusual neoplastic cell proliferation are still only partially understood. IVLBCL is considered stage IV lymphoma and manifests with a variety of nonspecific signs and symptoms. Patients with IVBCL usually do not present with lymphadenopathy. The tumor cells invade the blood vessels of multiple organs such as the central nervous system, skin, lungs, kidneys, and bone marrow. Common presenting symptoms are based on the organ affected and include mental status changes and fever of unknown origin. Although immunochemotherapy has significantly improved the often-poor prognosis of this kind of lymphoma, a large percentage of patient’s relapse. We present a 63-year-old man who had been diagnosed with high grade B cell lymphoma in the bone marrow in March 2021 and was in remission state after completing six cycles of chemotherapy. There was no abnormal FDG uptake on a post-chemotherapy PET/CT scan. Patient presented to the ER 1 year later with fever and dyspnea. The entire workup was completed and showed pancytopenia and elevated ESR. PET/CT scans revealed a widespread increase in FDG uptake in both the lungs and spleen. Lung biopsy revealed large, atypical cells only within alveolar septae and vessels that were positive for CD20 and PAX-5 and had high proliferation rate based on Ki67. The diagnosis of IVLBCL was made. IVLBCL has a low incidence rate with non-specific clinical presentation. The diagnosis can be easily missed in both clinical, radiological and the corresponding histopathological findings. Radiological finding and CT scan are not sensitive enough and may miss the lesion. Even though the PET/CT scan is more sensitive, the definitive diagnosis of IVLBCL relies mainly on histopathology and immunohistochemistry, at which point awareness and high suspicious of this entity by the pathologist is most necessary.