A 52-year-old woman with diabetes presents with progressive weakness of the right lower limb over 3 weeks. On examination, she has weakness of hip flexion (iliopsoas, L1–L2), knee extension (quadriceps, L3–L4), and ankle dorsiflexion (tibialis anterior, L4–L5). Sensory loss is noted over the right anterior thigh and medial leg (L3–L4 dermatomes). She denies bowel or bladder symptoms. MRI lumbar spine shows a large disc herniation at L4–L5 with nerve root compression. What is the most appropriate next step in management?