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: Surgery
In a middle aged male having back pain, syndesmophytes involving 4 continous veebrae are seen on Xray. The patient has ? 
Select and explain. 
A. DISH, B. Ankylosing spondylitis, C. Rheumatoid ahritis, D. Osteoahritis
B: Ankylosing spondylitis
Answer: B: Ankylosing spondylitis 
Explanation: Ans. is 'b' i.e., Ankylosing spondylitis Back pain with syndesmatophytes in a middle aged man suggest the diagnosis of ankylosing spondylitis.