A 62-year-old man from Delhi presents with progressive back pain for 3 months and recent onset lower limb weakness. On examination, he has tenderness over the lumbar spine. Laboratory investigations show hemoglobin 8.2 g/dL, serum creatinine 2.8 mg/dL, serum calcium 11.5 mg/dL, and serum albumin 2.1 g/dL. Serum protein electrophoresis reveals an M-spike of 4.2 g/dL in the gamma region. Bone marrow aspiration shows 35% plasma cells. MRI spine demonstrates compression fracture at L3 with epidural extension causing cord compression. What is the most appropriate immediate management?