Intravascular Large B-Cell Lymphoma Presenting with Rhabdomyolysis and Inflammatory Myositis: A Diagnostic Challenge

Intravascular large B-cell lymphoma (IVLBCL) is a rare and aggressive extranodal lymphoma characterised by the proliferation of lymphoma cells within small blood vessels. Distinctively, IVBCL typically lacks the lymphadenopathy, discrete tumour masses, or circulating lymphoma cells characteristic of other lymphomas. This results in substantial diagnostic delays and historically high rates of postmortem diagnosis. Common clinical features of IVLBCL include fever of unknown origin, cytopenias, elevated lactate dehydrogenase, and neurological dysfunction. This case highlights the diagnostic challenges of IVLBCL and an unusual presentation with rhabdomyolysis and inflammatory myositis.

An 80-year-old man presented with recurrent falls, progressive lower limb weakness, fever, and a left foot drop. Investigations revealed bicytopenia, acute kidney injury, and markedly elevated creatine kinase (peaking at 11,200 U/l). Despite extensive negative investigations including positron emission tomography scans and bone marrow biopsy, his condition deteriorated with progressive neurological impairment and evidence of myositis on magnetic resonance imaging (MRI). The diagnosis was established by random deep skin biopsies obtained from clinically normal-appearing skin.

IVLBCL should be considered in patients with unexplained fever, cytopenias, and neurological decline. Rhabdomyolysis and myositis-like MRI findings are rare but important manifestations. Random incisional skin biopsy is a key diagnostic tool, offering a high diagnostic yield even in the absence of cutaneous lesions. Early recognition of this clinical constellation and timely random skin biopsy can facilitate diagnosis and enable potentially life-prolonging therapy.

Intravascular large B-cell lymphoma (IVLBCL) should be suspected in older patients presenting with unexplained fever, cytopenias, elevated lactate dehydrogenase, and progressive neurological dysfunction, particularly when conventional imaging and bone marrow biopsies are unrevealing.IVLBCL may masquerade as an inflammatory myositis, representing an under-recognised manifestation of the disease.Random deep skin biopsy even from clinically normal-appearing skin is a valuable diagnostic tool in suspected IVLBCL, with reported diagnostic yields of above 75%; and should be performed early in the diagnostic workup.