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Unifocal psoriatic arthritis development in identical twins following site specific injury: evidence supporting biomechanical triggering events in genetically susceptible hosts
  1. Jennifer Ng1,
  2. Ai Lyn Tan2,3,
  3. Dennis McGonagle2,3
  1. 1Griffith University and Paradise Arthritis and Rheumatology, Southport, Australia
  2. 2NIHR Leeds Musculoskeletal Biomedical Research Unit, Chapel Allerton Hospital, Leeds, UK
  3. 3Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds, Leeds, UK
  1. Correspondence to Dr Dennis McGonagle, Leeds Institute of Rheumatic and Musculoskeletal Medicine, Chapel Allerton Hospital, Chapeltown Road, Leeds LS7 4SA, UK; d.g.mcgonagle{at}

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There have been reports suggesting that trauma or ‘deep Koebner phenomenon’ can precipitate the development of psoriatic arthritis (PsA).1 Both psoriasis and PsA have strong genetic associations, but there are no studies or reports on any potential interaction between environmental injury and genetics in the development of PsA. We describe the cases of identical twins with psoriasis who each developed PsA of the respective right and left second toes following foot injury.

A 54-year-old woman with a 15-year history of psoriasis kicked a table leg with her right foot. Thereafter, she developed pain and swelling of the second toe. X-ray of the foot did not show any fractures. An ultrasound showed marked synovitis of the right second toe with associated plantar plate rupture. She subsequently had surgical repair of the plantar plate, but the pain and swelling persisted. …

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  • Twitter Follow Ai Lyn Tan at @DrAiLynTan

  • Contributors Patient recruitment and data acquisition: JN. Case description and interpretation; manuscript preparation and final approval: JN, ALT and DM.

  • Competing interests None.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.