Pencil-in-cup deformity is the description given to one of the appearances on plain radiographs classically associated with psoriatic arthritis; however, it is not pathognomonic.
Radiographic features
The appearance results from periarticular erosions and bone resorption giving the appearance of a pencil in a cup.
Differential diagnosis
Although classically described with psoriatic arthritis, this appearance can also be seen in:
- systemic sclerosis 2
- rheumatoid arthritis
- reactive arthritis
- Behçet disease: case reports 3
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