Not All Lytic Bone Lesions Are Metastases: Delayed Diagnosis of Multiple Myeloma in a Cancer Survivor

Background: In patients with established malignancy, new osteolytic lesions are often attributed to metastatic disease.Such assumptions may obscure alternative diagnoses, including plasma cell dyscrasias.Cognitive biases may contribute to delayed diagnosis.Case Report: A 77-year-old female with a history of lung cancer presented with progressive severe back pain.Magnetic resonance imaging demonstrated multiple vertebral lesions initially interpreted as metastatic disease.Despite the absence of visceral recurrence, multidisciplinary consensus favored metastases, with osteoporosis as a differential diagnosis, and osteoporosis therapy was initiated.However, symptoms persisted, prompting further evaluation.Skeletal survey demonstrated classic punched-out skull lesions.Serum protein electrophoresis and free light chain analysis confirmed immunoglobulin G kappa monoclonality, and bone marrow biopsy revealed 80% clonal plasma cells, establishing Revised International Staging System stage II multiple myeloma.After disease-specific therapy, the patient's pain resolved completely, and she achieved a very good partial response.Conclusion: This case illustrates anchoring bias, diagnostic momentum, and overreliance on advanced imaging in a patient with prior cancer.Multiple myeloma should remain in the differential diagnosis of diffuse osteolytic bone disease even in the absence of complete CRAB criteria: hypercalcemia, renal impairment, anemia, and bone lesions.Early use of plain radiographs and monoclonal protein testing may prevent diagnostic delay.