<prompt> Differentiating point between psoriatic and rheumatoid arthritis and ankylosing spondylitis?Pencil-in-cup deformityTelescoping of phalangesMarginal erosionsAll of the above  <response>: Ans. d All of the above Ref. Harrison 18th 1998PSORIATIC ARTHRITIS Characteristics of peripheral PsA include DIP involvement, including the classic pencil-in-cup deformity; marginal erosions with adjacent bony proliferation whiskering; small joint ankylosis; osteolysis of phalangeal and metacarpal bone, with telescoping of digits; and periostitis and proliferative new bone at sites of enthesitis. Characteristics of axial PsA include asymmetric sacroiliitis; compared with idiopathic AS, less zygoapophyseal joint arthritis, fewer and less symmetric and delicate syndesmophytes; fluffy hyperperiostosis on anterior vertebral bodies; severe cervical spine involvement, with a tendency to atlantoaxial subluxation but relative sparing of the thoracolumbar spine; and paravertebral ossification.Types True psoriatic arthritis 31 Psoriatic arthritis resembling RA 38 Concomitant RA with psoriatic arthritis 31Radiological Features Hands:- Asymmetrical involvement- Ray distribution all 3 joints of single ray involved; DIP, PIP, and MCP- Sausage digits- Absence of osteoporosis- Sparing of joint space early- Erosions at DIP Gull wing appearance- Cup-like erosions- Fluffy periosteal reaction- Productive bone changes periosteal reaction and Proliferative new bone formation- Mouse ear sign joints flanked by fluffy new bone formation- Pencil in cup or pestle in mortar deformity- Opera glass or Main-en-lorgnette deformity or telescoping- Tapering of proximal phalanges- Acroosteolysis- Ivory phalanx- No ulnar deviation- Fibular digital deviation- Sharply demarcated adjacent bony surface pathognomonic- Spontaneous joint fusion- Destruction of IP joints of hands and feet with abnormal widening of joint space- Neurotrophic changes at DIP joints with Ticked candy appearance- Arthritis mutilans Feet:- Similar changes as that of hand, Feet affection less common and less severe than Reiters syndrome- Sausage toes, Characteristic early changes at IP joints of great toe Axial skeleton SI joints and spine:- Unilateral involvement common, when bilateral it is asymmetrical- Sacroilitis similar to AS, except that joint fusion does not occur and affection is asymmetrical Enthesitis Paravertebral ossificationsparasyndesmophytes unilateral, asymmetrical Extraarticular involvement:, Silvery skin scales and Thimble pitting of nails. 