A 68-year-old male presents with fatigue, back pain, and recurrent infections for 6 months. On examination: Pale, mild tenderness over the lumbar spine. Lab Findings: CBC: Hb 9.8 g/dL, WBC 4,500/µL, Platelets 210,000/µL. Serum calcium: 12.5 mg/dL (elevated). Renal function: Creatinine 2.1 mg/dL (elevated). Serum protein electrophoresis (SPEP): Monoclonal M-spike (IgG). Urine Bence Jones protein: Positive. Skeletal survey: Multiple lytic lesions in vertebrae. Bone marrow biopsy: >10% plasma cells. Key Clinical Features: Elderly patient with bone pain, anemia, renal dysfunction, and hypercalcemia → Suggestive of multiple myeloma. M-spike on SPEP + bone marrow plasma cell infiltration confirms diagnosis. Recurrent infections due to immunoglobulin suppression. Differential Diagnosis: MGUS (Monoclonal Gammopathy of Undetermined Significance) – M-spike <3 g/dL, no organ damage. Waldenström Macroglobulinemia – IgM monoclonal spike, hyperviscosity symptoms. Metastatic bone disease – No monoclonal protein, solid tumor history. Investigations & Workup: Serum and urine protein electrophoresis → Detect monoclonal protein. Bone marrow biopsy → Confirms >10% plasma cells. Imaging (X-ray/MRI/PET-CT) → Look for lytic lesions. Cytogenetics (FISH analysis) → Prognostic markers (e.g., del(17p), t(4;14)). Final Diagnosis & Management Plan: Diagnosis: Multiple Myeloma (IgG subtype). Treatment: Initial therapy: Bortezomib + Lenalidomide + Dexamethasone (VRd). Autologous stem cell transplant (ASCT) for eligible patients. Bisphosphonates (e.g., Zoledronic acid) for bone protection. Supportive care: Infection prophylaxis, renal protection. MCQs with Answers & Explanations: Q1. What is the most common monoclonal protein in multiple myeloma? A) IgA B) IgG C) IgM D) Free light chains ✔ Correct Answer: B) IgG Explanation: IgG is the most common monoclonal protein in multiple myeloma (60–70%), followed by IgA. IgM is characteristic of Waldenström macroglobulinemia.
