## **Core Concept**
Ankylosing spondylitis (AS) is a type of seronegative spondyloarthropathy that primarily affects the axial skeleton, but it can also have extra-articular manifestations. These extra-articular manifestations can involve various systems and are significant in the overall management of the disease.

## **Why the Correct Answer is Right**
The most common extra-articular manifestation of Ankylosing spondylitis is **acute anterior uveitis**, also known as acute iritis. This condition is characterized by inflammation of the uveal tract of the eye, leading to symptoms such as eye pain, redness, and sensitivity to light. The exact mechanism is not fully understood, but it is believed to be related to the systemic inflammation seen in AS. The inflammation in AS is driven by **TNF-alpha** and other cytokines, which can lead to the activation of immune cells and subsequent inflammation in various tissues, including the eye.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While gastrointestinal symptoms can be associated with AS, particularly in the context of inflammatory bowel disease (IBD), they are not the most common extra-articular manifestation.
- **Option B:** Cardiovascular involvement, such as aortitis and aortic regurgitation, can occur but is less common than acute anterior uveitis.
- **Option C:** Neurological manifestations can occur, including cauda equina syndrome, but again, these are less common than acute anterior uveitis.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that acute anterior uveitis in AS is often **asymptomatic** but can lead to severe complications if not treated promptly. Patients with AS should be regularly screened for eye symptoms, and any suspicion of uveitis should prompt an urgent ophthalmological evaluation.

## **Correct Answer:** . Acute anterior uveitis (or acute iritis)