This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immune system, Subject name: Medicine
What is the most common extra aicular manifestation of ankylosiing spondylitis? 
Select and explain. 
A. Anterior uveitis, B. Aoic regurgitation, C. Cataract, D. Inflammatory bowel disease
A: Anterior uveitis
Answer: A: Anterior uveitis 
Explanation: Extra aicular manifestations of ankylosing spondylitis Up to 40% of patients also have peripheral musculoskeletal lesions (asymmetrical, affecting entheses of large joints, such as the hips, knees, ankles and shoulders).Fatigue is a major complaint and is common to all SpAs, but its cause is unknown. Acute anterior uveitis is the most common extra-aicular feature, which occasionally precedes joint disease Ref Davidson 23e p1030