Professional and Linguistic Assessments Board (PLAB) Practice Exam

What characteristic X-ray finding is associated with psoriatic arthritis?

1. Bony erosion

2. Pencil-in-cup appearance

3. Joint space narrowing

4. Soft tissue swelling

The correct answer is: Pencil-in-cup appearance

The pencil-in-cup appearance is a distinctive characteristic X-ray finding associated with psoriatic arthritis. This term describes the erosion and deformity of the phalangeal bones, particularly at the distal and proximal joints, where the bone ends appear to be shaped like a pencil fitting into a cup. This feature is indicative of the unique bone changes that occur as part of psoriatic arthritis, reflecting the underlying pathophysiology of inflammation and bone remodeling typical in this condition. In psoriatic arthritis, the inflammatory process not only affects the joints but also leads to significant changes in the bone structure. The pencil-in-cup appearance specifically illustrates the combination of bony erosion and the reactive changes that result in this distinctive shape, highlighting the erosion and wear at the joint surfaces. Other findings such as bony erosion, joint space narrowing, and soft tissue swelling can occur in various forms of arthritis but are not as uniquely characteristic of psoriatic arthritis as the pencil-in-cup appearance. These changes can be seen in other conditions, making them less specific to psoriatic arthritis itself. Thus, the pencil-in-cup appearance stands out as a hallmark finding in the diagnosis of this specific type of inflammatory arthritis.