**2. Methods**

This was a single-center non-interventional retrospective study that examined patients with PsA who were diagnosed by rheumatologists and dermatologists at our hospital between January 2010 and December 2018. All patients in this study satisfied the CASPAR criteria with a score of more than 3 points. A total of 64 consecutive cases were enrolled, and informed consent was obtained from each patient. This study was approved by Niigata University Medical and Dental Hospital Institutional Review Board (#2018–0418).

The patients were categorized and investigated according to the following PsA onset patterns: a skin rash that preceded the manifestations of arthritis (skin leading type), the osteoarticular lesion that preceded the manifestation of a skin rash (osteoarticular leading type), and the simultaneous onset of skin and osteoarticular symptoms (simultaneous type). For both the skin and osteoarticular leading types of PsA, we recorded the time between the presentation of the first and second symptoms. We also investigated the disease prevalence according to the lesion site, namely peripheral lesions (e.g., fingers, wrists, elbows, shoulders, toes, ankles, knees, and hips), axial lesions (e.g., cervical, thoracic, lumbar spines, and sacroiliac joint), and enthesitis (e.g., Achilles' tendon, plantar aponeurosis, quadriceps tendon, and patellar tendon).

When arthritis symptoms were present, painful areas were evaluated by radiography, which allowed us to confirm the presence of imaging findings typical of PsA (typical peripheral joint new bone formation, sacroiliac joint bone erosions, and syndesmophytes on the sacroiliac joint or spine).

Obesity was defined as a body mass index (BMI) ≥ 25, and the prevalence of comorbidities was assessed relative to that of the general population as reported in a survey conducted by the Ministry of Health, Labor, and Welfare of Japan [9]. The incidences of obesity and hypertension, diabetes mellitus, and other diseases such as dyslipidemia and chronic kidney disease were examined.

Furthermore, we classified the patients according to the treatments they had received, such as nonsteroidal anti-inflammatory drugs (NSAIDs), conventional synthetic disease-modifying antirheumatic drugs (csDMARDs), biological DMARDs (bDMARDs), prednisolone, and others.
