When the Liver Lies: Plasma Cell Myeloma Mimicking Hepatic Metastasis of Unknown Primary — A Pathological Perspectiv

Abstract

Background: Extramedullary plasma cell myeloma (PCM) with hepatic space-occupying lesions mimicking hypervascular metastases of unknown primary is exceedingly rare and diagnostically challenging. Case Summary: A 60-year-old male with T2DM presented with back pain and bilateral lower limb weakness. Imaging revealed multiple hypervascular hepatic lesions, peripancreatic calcified masses, and extensive lytic skeletal lesions with D11 vertebral compression fracture. Tumour markers were normal. EUS-guided fine needle biopsy (EUS-FNB) yielded cores showing small round blue cells in sheets with eccentric nuclei and salt-and-pepper chromatin. Immunohistochemistry (IHC) demonstrated diffuse membranous CD138 positivity with synaptophysin negativity, confirming plasma cell myeloma. Conclusion: EUS-FNB with IHC is pivotal in establishing the pathological diagnosis of hepatic extramedullary myeloma, preventing misdiagnosis as an epithelial metastasis and ensuring timely haematological management.