Imaging findings of sterile pyogenic arthritis, pyoderma gangrenosum and acne (PAPA) syndrome: differential diagnosis and review of the literature.

Pyogenic arthritis, pyoderma gangrenosum and acne (PAPA) syndrome is a rare autosomal-dominant autoinflammatory disease of incomplete penetrance and variable expression. PAPA syndrome is the result of a mutation in the proline serine threonine phosphatase-interacting protein 1 (PSTPIP1/CD2BP1) gene located on chromosome 15, which results in an abnormal overproduction of the pro-inflammatory cytokine interleukin-1β (IL-1). This syndrome clinically manifests as early onset of recurrent episodes of acute aseptic inflammation of the joints, generally occurring in the first two decades of life, followed by manifestation of characteristic skin lesions in the third decade, after an obvious decline in the joint symptoms. Although uncommon, the potential clinical implications of PAPA syndrome warrant an appropriate diagnosis in a timely fashion.