Differential Diagnosis for Lytic Lesions in PET Scan with 14% Plasma Cells in Bone Marrow and Inconclusive Serum Electrophoresis

• Single Most Likely Diagnosis
  • Multiple Myeloma: This is the most likely diagnosis given the presence of lytic lesions on PET scan and 14% plasma cells in the bone marrow. Although serum electrophoresis is inconclusive, the combination of imaging and bone marrow findings strongly suggests multiple myeloma, especially if other criteria such as anemia, renal failure, or hypercalcemia are present.
• Other Likely Diagnoses
  • Monoclonal Gammopathy of Undetermined Significance (MGUS): Given the presence of 14% plasma cells, which is below the typical threshold for multiple myeloma diagnosis, and inconclusive serum electrophoresis, MGUS could be considered, especially if other myeloma-defining events or end-organ damage are not present.
  • Plasma Cell Leukemia: Although less common, plasma cell leukemia could present with a lower percentage of plasma cells in the bone marrow if the disease is primarily circulating in the blood. However, this would typically be associated with more pronounced cytopenias and other systemic symptoms.
• Do Not Miss Diagnoses
  • Lymphoma: Certain types of lymphoma, such as mantle cell lymphoma or lymphoplasmacytic lymphoma, can present with bone marrow involvement and lytic lesions. Missing a diagnosis of lymphoma could lead to significant morbidity and mortality due to delayed appropriate treatment.
  • Metastatic Cancer: Metastatic disease from solid tumors (e.g., breast, lung, or renal cell carcinoma) can cause lytic lesions and might be associated with a minor increase in plasma cells in the bone marrow due to reactive changes. Failing to diagnose metastatic cancer could result in inappropriate treatment and poor outcomes.
• Rare Diagnoses
  • POEMS Syndrome: A rare paraneoplastic syndrome associated with a plasma cell disorder, characterized by polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes. The presence of lytic lesions and plasma cells could be part of this syndrome, although other characteristic features would need to be present.
  • Amyloid Light-chain (AL) Amyloidosis: This condition involves the deposition of amyloid fibrils composed of immunoglobulin light chains produced by a clonal plasma cell population. While it can present with systemic symptoms and organ dysfunction, the presence of lytic lesions would be less typical, making it a rare consideration in this context.