A 52-year-old man from Delhi presents to the pain clinic with chronic neuropathic pain in his lower limbs following a spinal cord injury 18 months ago. He reports burning pain, allodynia, and hyperalgesia. He has already tried gabapentin and pregabalin without adequate relief. On examination, he has intact motor function but diminished sensation below the level of injury. What is the most appropriate next step in management to target the underlying pain pathway dysfunction?