1. Definition: Psoriatic arthritis (PsA) refers to an inflammatory arthritis associated with psoriasis. It was previously considered a subtype of rheumatoid arthritis, but is now recognized as an independent disease and a member of the spondyloarthropathy family. 2, disease course characteristics: psoriatic arthritis has intermittent episodes and remission, but 70% of these patients have progressive aggravation of joint damage. 3.Incidence and prevalence and epidemiology Characteristics: The prevalence of psoriatic arthritis in the general population is 0.25% (25 out of 1000 people have psoriatic arthritis). A foreign community-based study found that the sex- and age-adjusted prevalence of psoriatic arthritis was 0.036% in 1970-1979 and 0.098% in 1990-2000, reflecting a significant trend of increasing prevalence of psoriatic arthritis. Domestic and international research reports confirm that the prevalence of PsA in patients with psoriasis is much greater than that in the general population, ranging from 5% to 48%. In China, a scholar investigated 1928 patients with psoriasis and found 112 patients with PsA, with a prevalence of 5.8%. Why is there such a large difference in the prevalence data? It may be related to factors such as ethnicity (i.e., genetics) and research methods, but in any case it does not affect the following conclusion: PsA is not uncommon among psoriasis patients and the trend is increasing year by year. Most PsA patients develop psoriasis first and joint damage later. A community-based study abroad found that in such patients, joint damage occurred on average 7 years after the onset of psoriatic lesions; in addition, the study found that 15-20% of PsA patients had joint damage first and psoriatic lesions later. 4. Clinical distribution of PsA patients Characteristics: It is generally believed that there is no difference in the prevalence of PsA between men and women, whether in the general population or among psoriasis patients. However, a recent study found a slightly higher prevalence in men than in women. One study found 196 men and 127 women with PsA per 100,000 in the general population, and two other studies found PsA prevalence rates of 6.4% and 10.4% in men and 3.9% and 6.6% in women with psoriasis, respectively. The peak age of PsA in female psoriasis patients was around 60 years old, while the peak age of PsA in male psoriasis patients was less than that of females. This is in line with the characteristic that the average age of psoriasis occurs later in women than in men. 5.How many PsA patients are there in China The results of the national epidemiological sample survey of psoriasis in 1984 confirmed that the prevalence of psoriasis was 0.123%, and according to this data, there are 16.6 million psoriasis patients in China, and the prevalence of PsA among psoriasis patients is 5.8%, and according to the data of 1094, it is estimated that there are 960,000 PsA patients in China. Many literature reports that the prevalence of psoriasis has a tendency to increase year by year, so the actual number of PsA patients in China will be significantly more than 960,000. 6.Clinical manifestations of psoriatic arthritis PsA can occur in large joints (such as: knee joints, elbow joints, ankle joints, etc.), but also accumulate small joints (such as: finger and toe joints) and the spine, that is, it can occur symmetrically or asymmetrically. The main clinical symptoms are pain and impaired movement in the joint area, which can lead to loss of joint function and disability in severe cases. Foreign studies have reported that women with PsA are more likely to have symmetric polyarthritis; men are more likely to have spinal arthritis. Patients with PsA at a young age are more likely to have deformation and destruction of joints. 7.Which psoriasis patients are more likely to have PsA Since most PsA patients have psoriasis lesions first, many dermatologists study the relationship between psoriasis lesions and PsA in an attempt to discover regular features for early warning and detection of PsA, although there are differences in research results, it is currently believed that psoriasis patients with the following features have a higher possibility of having PsA (1) Patients with psoriasis occurring on the scalp; (2) Patients with psoriasis involving more than three sites; (3) Patients with psoriasis with nail dystrophy; (4) Patients with psoriasis occurring in the gluteal sulcus and perianal area The early age of occurrence of psoriatic lesions has little relationship with the occurrence of PsA. 8. The effect of PsA on human health Patients with PsA often feel fatigue and have reduced body functions compared with normal people. The average score of PsA patients was 58.8 and the average score of the general population was 72.0. Another researcher showed that PsA patients have the same score of ability and quality of life as rheumatoid arthritis patients. PsA has now been shown to be a progressive, systemically disabling disease. Disabling joint destruction occurs within 2 years of the onset of polyarticular damage in approximately half of patients presenting with polyarticular arthritis. PsA can also increase the risk of death, with one study finding a 65% increased risk of death in men and 59% in women with PsA compared to the general population. Patients with the following clinical features are predicted to have an increased risk of death (1) Imaging damage to the joints is demonstrated. (2) Blood sedimentation greater than 15 (ESR > 15). (3) The presence of nail damage. The main causes of death in patients with PsA are similar to those in the general population. 9, the diagnosis of PsA Foreign scholars Moll and Wright were the first scientists to propose the diagnostic criteria for PsA, which is still the simplest and most applied diagnostic criteria. PsA can be diagnosed if the following conditions are met: inflammatory arthritis (peripheral arthritis and or sacroiliac arthritis). Have psoriatic skin lesions. Have a negative serum rheumatoid factor. Of the above criteria, determining the presence or absence of inflammatory arthritis is the more difficult task. It is difficult for clinicians to determine whether pain in joints, tendons or ligaments is caused by inflammatory disease or by degenerative disease, trauma or crystalline arthritis (e.g., gout). The site of psoriatic arthritis differs from that of arthritis caused by other diseases, as PsA more commonly involves the distal interphalangeal joints, unlike rheumatoid arthritis.