A 54-year-old male with a 5-year history of rheumatoid arthritis (RA) reports worsening arthralgia in the finger joints of both hands over the past 2 months, with morning stiffness lasting about 1 hour. He has never received formal systematic treatment. Examination reveals synovial thickening in the 1st and 2nd MCP joints of both hands, swelling and marked tenderness in the 2nd to 4th proximal interphalangeal (PIP) joints of the right hand, and swelling with tenderness in the 2nd and 3rd PIP joints of the left hand. X-ray shows disappearance and fusion of the bone spaces in both wrists, with marked narrowing of the metacarpophalangeal and proximal interphalangeal joint spaces. Based on the X-ray findings of both hands, which stage of RA does this patient belong to?