A 38-year-old male factory worker from Mumbai presents with a 2-month history of progressive pain and numbness in the medial aspect of his hand, with recent onset of weakness in finger abduction and adduction. On examination, he has a positive Froment's sign and Wartenberg's sign. Sensation is intact over the dorsal aspect of the hand. Nerve conduction studies show normal conduction velocity in the ulnar nerve at the elbow and wrist, but reduced amplitude of the compound muscle action potential (CMAP) in the intrinsic hand muscles. What is the most appropriate next step in management?