Mithraa Devi Sekar, Enosh Katta, Manasa Raj, Chinmay Parale, Ramanathan Velayuthan, Prabhu Manivannan*, Arun Kumar, Avinash Anantharaj, Rakhee Kar, Nachiappa Ganesh Rajesh
Light-Chain Plasma Cell Myeloma (LC-PCM) is a more aggressive and a less frequent type of PCM with poorer prognosis. It is characterized by the inability of the malignant plasma cells to produce heavy chains and resulting in the exclusive production of light chains. We present a case of LC-PCM with two diagnostic challenges that were faced during the diagnosis: the first was increased plasma cells (65%) in the bone marrow without any CRAB features (hypercalcemia, renal failure, anemia, and lytic bone lesions) primarily presenting as cardiac failure which is an uncommon finding. The second challenge was serum protein electrophoresis with immune fixation revealed no heavy chains along with a serum-free light chain ratio of 0.011. Myeloma defining events described in recent WHO classification along with biomarkers for diagnosing PCM helped us in arriving at the diagnosis of LC-PCM. Another diagnostic issue was the presence of prominent interstitial and vessel wall deposition of eosinophilic and extracellular amorphous material. This material was negative for periodic acid-Schiff stain and Congo red and did not show any apple green birefringence on polarization microscopy, black in silver, and blue in trichrome stains suggesting the presence of idiopathic amyloid-like deposits.