Background Psoriatic arthritis (PsA) is characterised by involvement of both the appendicular and axial skeleton. The reported prevalence of sacroiliitis (SI) in patients with PsA is quite variable and ranges from 30% to 78%. Little is known about the clinical predictors of sacroiliitis, especially regarding underlying patient’s characteristics, life style, correlation with skin disease and the severity of psoriatic disease.
Objectives The objectives of our study were: 1) To investigate the prevalence of SI in an ethnically homogenous consecutive cohort of established PsA, 2) to identify clinical predictors of SI in patients with PsA, 3) to describe different patterns of SI and their associations, if any, with clinical characteristics.
Methods A consecutive cohort of 283 PsA patients attending rheumatology clinics at St Vincent’s University Hospital, Dublin was included. Following informed consent, patients underwent a detailed skin and rheumatologic assessment including disease activity measures [PASI, Body Surface Area (BSA) for Psoriasis (Ps); DAS 28 CRP], CRP and ESR, HAQ, Dermatology Life Quality Index (DLQI), Bristol Rheumatoid Arthritis Fatigue Numeric Rating Scale (BRAF-NRS), EuroQuol questionnaire (EQ5D), and radiographs were taken for involved joints along with hands, feet and sacroiliac joints. Other risk factors studied were gender, smoking habits, BMI, family history of Ps & PsA, different types of Ps, psoriatic nail disease, duration of Ps and PsA, enthesitis, dactylitis, prior DMARDs usage, psoriatic disease requiring TNFi, erosions, arthritis mutilans, educational attainment, insulin resistance, metabolic syndrome. In addition, an extensive medical record review was performed to obtain information regarding their previous psoriatic disease features. We defined the criteria for identifying SI if ≥ grade 2 radiographic changes were present (unilateral or bilateral). Asymmetrical SI was labelled when grades were different between 2 SI joints, and unilateral SI was labelled when the opposite SI joint was completely uninvolved.
Results A total of 283 PsA patients [mean age 55±12 years; 52% female; mean PsA duration=19±9 years] were studied. Twenty five percent (71/283) of the cohort had radiographic SI; all either had present or past history of backache. Mean age of patients with SI was 51.6±11 years, and 53.5% were male. SI was asymmetrical in 77.5% (n=51), but SI was bilateral in 62% (34 out of 51) of these patients. The asymmetrical SI group were noted to be more female (p=0.050) with less nail disease (p=0.02), and less enthesitis (p=0.002). On univariate analysis, SI was noted to have significant association with younger age (p=0.01), longer duration of PsA (p=0.001), younger age of Ps and PsA onset (p=<0.001 each), higher PASI score (p=0.01), peripheral joint erosions (p=0.008), and maximum CRP and ESR achieved during the disease course (p=0.009, 0.03, respectively). On backward step-wise multiple regression analysis, model predicted significant association of erosions (OR 1.9, p=0.02), PsA age of onset (OR 0.94, p=<0.001), and PASI max (OR 1.06, p=0.02) with SI.
Conclusions Twenty five percent of PsA patients developed SI on long-term follow up, and SI was asymmetrical in more than two third of these cases. Erosive peripheral arthritis, severe skin Ps, and earlier onset of PsA were positively associated with developing SI.
Disclosure of Interest None Declared
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