Palindromic rheumatism (PR) is an episodic arthropathy characterised by recurrent attacks of short-lasting articular and periarticular inflammation without residual joint involvement. Although definite knowledge on the disease entity of PR is lacking, the clinical and immunological similarities and the frequent progression to chronic arthritis may suggest a pathogenic relationship with rheumatoid arthritis (RA).1 2 In particular, anticitrullinated protein antibody (ACPA)-positive PR has been regarded as a prodromic phase of RA.3 Compared with autoantibody-positive arthralgia, a well-established model of preclinical RA,4 ACPA-positive PR shows a clearly detectable articular phase and might thus represent a very early self-remitting stage of the disease.

Typical attacks of PR may escape definite joint effusion at clinical examination, in spite of considerable periarticular and para-articular swelling, pain and loss of function.1 More accurate identification of the anatomical targets of PR might expand our knowledge on the mechanisms of disease initiation in very early RA before its full-blown clinical stage. We have undertaken a study to characterise the imaging correlates of acute arthritis in ACPA-positive PR.

Inclusion criteria were: (1) fulfilment of the diagnostic criteria for PR1; (2) an …