Cardiovascular Involvement of a CD138-Negative Anaplastic Myeloma: A Diagnostic Dilemma

Anaplastic myeloma (AM) is an extremely rare and aggressive histological variant of myeloma. It is characterized by extramedullary presentation in the young and has a poor prognosis. It can be a diagnostic challenge when myeloma is not suspected and even more when the immunophenotype is unexpected. We present a rare presentation of anaplastic myeloma with cardiovascular involvement. Though the patient did not have the typical clinical features of myeloma, except lytic lesion in the femur, the cardiac biopsy showed sheets of anaplastic cells, and some with multinucleation. There were also some areas with a more plasmacytoid appearance. The initial immunohistochemical panel was negative for CD3, CD20, CD138, AE1/3, and kappa. It was positive for lambda. This led to an extended panel which showed positivity for CD79a and MUM1 and negative for LMP-1, HHV-8, CD43, CD117, CD56, and CD30. Even the flow cytometry on the bone marrow showed a small population of atypical cells positive for CD38 and negative for CD138 with lambda restriction. This is an unusual case of anaplastic myeloma with cardiovascular involvement and CD138 negativity. This case highlights the need to add a panel of plasma cell markers when myeloma is suspected, and it is pertinent to read flow cytometry with caution to avoid missing atypical plasma cells which maybe CD38+/CD138-.