This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Orthopaedics
[{'content': 'A 65-yr-old man with H/O back pain since 3 months. ESR is raised. On examination marked stiffness and mild restriction of chest movements is found. On x-ray, syndesmophytes are present in vertebrae. Diagnosis is - \nSelect and explain. \nA. Ankylosing spondylitis, B. Degenerative osteoarthritis of spine, C. Ankylosing hyperosteosis, D. Lumbar canal stenosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The clinical profile of the given case fits into Ankylosing spondylitis (A.S.) except for the age.\nA.S. is usually seen in 2nd or 3rd decades of age with a median age of 23. However "in 5% ofpatients, symptoms begin after 40" - Harrison\nAll other features, i.e. raised ESR, marked stiffness, restriction of chest movements & syndesmophytes are seen in A.S.', 'role': 'assistant'}]