psoriatic arthritis CHORUS

Description: types:
1. true psoriatic arthritis (1/3)
2. resembling rheumatoid arthritis (1/3)
3. combination of psoriatic and RA (1/3)
findings:
* no juxta-articular osteoporosis (unlike RA)
* periosteal reaction frequent
* assymetrical destruction of DIP with ankylosis
* resorption of terminal tufts with "pencil in cup" deformity
* ivory phalanx
* destruction of 1st toe IP joint with periosteal reaction and bony proliferation at distal phalangeal base (PATHOGNOMONIC)
* assymetrical syndesmophytes (lower C- to upper L-spine)
* squaring of vertebrae in L-spine
* paravertebral soft tissue calcifications
* bilateral assymetrical sacroiliitis
a/w HLA B-27 antigen, negative rheumatoid factor