Clinical Characteristics of "Severe" Peripheral Psoriatic Arthritis: A Retrospective Analysis of a Longitudinal Cohort

Introduction The concept of severity in a multidomain disease such as psoriatic arthritis (PsA) is still not well defined. The aim of this study was to identify the clinical characteristics of patients with severe peripheral PsA. Methods Retrospective analysis of a longitudinal cohort. Demographic and clinical characteristics of patients with PsA were collected at baseline and at last follow-up. We defined the severe population using the modified Composite Psoriatic Disease Activity Index (mCPDAI); which excludes ankylosing spondylitis quality of life scale). Hence, patients with a score of 3 in at least one domain were defined as having severe PsA. Clinical characteristics of patients fulfilling the definition of severe PsA were compared to those non-severe. Results We evaluated 177 patients with peripheral PsA (M/F: 98/76). Of these, 64 (36.1%) were identified as severe according to the mCPDAI criteria, at baseline. Eighteen patients (10.1%) at last follow-up still met the definition of severe PsA. At last follow-up visit, severe patients with PsA were only males (18/18, P < 0.01) and have worse outcomes in terms of disease activity, pain, function, and impact of disease. Male sex and the severity of skin involvement at baseline were factors associated with the presence of severe PsA. The agreement between the presence of severe PsA and the absence of minimal disease activity was slight [Cohen's k: 0.174 (0.084-0.264)]. Conclusions Our study showed that severe patients with PsA had more disease activity, pain, and impact of disease than non-severe patients. Furthermore, we demonstrated that severity and disease activity are not interchangeable concepts.