Radiographic scoring systems for psoriatic arthritis are insufficient for psoriatic arthritis mutilans: results from the Nordic PAM Study

BACKGROUND: Psoriatic arthritis mutilans (PAM) is the most severe phenotype of psoriatic arthritis (PsA). PURPOSE: To describe the radiological features in PAM and explore whether existing scoring systems for radiological damage in psoriatic arthritis are applicable for PAM. MATERIAL AND METHODS: Radiographs were scored according to the modified Sharp-van der Heijde (mSvdH) and the Psoriatic Arthritis Ratingen Score (PARS) systems for PsA. RESULTS: At inclusion, 55 PAM patients (49% women, mean age 58 ± 12 years) had conventional radiographs of both hands and feet. A total of 869 PAM joints were detected and 193 joints with ankylosis. The mean total mSvdH score was 213.7 ± 137.8 (41% of maximum) with a higher score for hands than for feet: 136.6 ± 90.1 vs. 79.1 ± 60.9. However, the total score was relatively higher in the feet than in the hands when compared to the highest possible scoring (47% vs. 38% of max). The mean total PARS score was 126.3 ± 79.6 (35% of max). Scoring for joint destruction was higher than for proliferation (22% vs. 11% of max). Strong correlation was found between mSvdH and PARS (r(2) = 0.913). A significant correlation was found between scoring and duration of arthritis and the Health Assessment Questionnaire. History of smoking, BMI, and gender did not influence the scoring values. CONCLUSIONS: The two scoring systems studied may not be ideal to indicate progression of PAM in advanced disease since they reach ceiling effects rather early. Therefore, reporting early signs suggestive of PAM, e.g. signs of pencil-in-cup deformities or osteolysis, is crucial. This would reveal the presence of PAM and might lead to improved treatment in order to minimize joint damage.