Inflammatory posterior interosseous nerve palsy in a patient with psoriatic arthropathy

Summary Psoriasis is a chronic, relapsing, inflammatory skin disorder with a strong genetic basis. Five patterns of psoriatic arthritis have been identified: asymmetrical oligoarticular arthritis, symmetrical polyarthritis, distal interphalangeal arthropathy, arthritis mutilans and spondylitis with or without sacroiliitis. Extra-articular disease is uncommon. We report a rare case of an inflammatory posterior interosseus nerve palsy in a patient with known psoriatic arthropathy, where investigation warranted medical treatment over a surgical approach. The commonest cause of posterior interosseus nerve palsy is entrapment at the proximal forearm. Other possible aetiologies include extension of elbow synovitis as described in rheumatoid arthritis, trauma eg. Monteggia fractures, tumours and iatrogenic injuries. We discuss the diagnostic dilemma and the management issues for upper limb surgeons.