Differentiating point between psoriatic and rheumatoid arthritis and ankylosing spondylitis?

Ans. d (All of the above) (Ref. Harrison 18th/ 1998)PSORIATIC 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 (31%)Radiological 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 Reiter's 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 ossifications/parasyndesmophytes (unilateral, asymmetrical)# Extraarticular involvement:, Silvery skin scales and Thimble pitting of nails.