In the past, we diagnosed psoriatic arthritis mainly using the Moll & Wright diagnostic classification criteria from the 1970s, which were not tested in different populations and had low sensitivity and specificity. The CASPAR (Classification Criteria for the Study of Psoriatic Arthritis study) diagnostic criteria, which was developed by a consortium of 31 experts and validated in 588 patients with psoriatic arthritis and 536 patients with other inflammatory arthritis, are now commonly used internationally. The diagnostic sensitivity and specificity reached 91,4% and 98,7%, respectively. Specific criteria were as follows: Established inflammatory skeletal muscle disease (joint, spine, or tendon end) with at least 3 of the following: 1. Psoriasis: (a) current presence of a psoriatic rash or scalp disease as determined by a qualified health professional and/or (b) history of psoriasis obtained from the patient or qualified health professional and/or (c) history of psoriasis in their 1st or 2nd degree relative as provided by the patient. 2, Nail changes:Current examination reveals typical psoriatic nail dystrophy, including peeling, depressed and hyperkeratotic nails. 3, RF negative. 4. Finger (toe) inflammation: (a) current swelling throughout the finger (toe) and/or (b) history of finger (toe) inflammation documented by a qualified health medical professional 5. Radiographic evidence of new bone formation adjacent to joints: vague ossification near the joint space on hand or foot x-ray (but exclude bone formation).