Background/Purpose: Arthritis mutilans (AM), a severe form of psoriatic arthritis (PsA), is characterised clinically by digital shortening resulting from osteolysis and/or erosions. It is still unclear whether AM is simply the end-stage of polyarticular PsA, or whether it is a unique entity with different pathogenic mechanisms. Given its rarity, there is little data regarding its clinical and laboratory associations. The objectives of our study were 1) to investigate the prevalence of AM in an ethnically homogenous consecutive cohort of established PsA, 2) to identify the clinical phenotype of AM and its effect on quality of life, functional impairment and fatigue scores compared to those PsA patients who do not have AM.

Methods: A cohort of 283 consecutive PsA patients, fulfilling CASPAR criteria, was included. Following informed consent, patients underwent detailed skin and rheumatologic assessments including disease activity measures [PASI, Body Surface Area (BSA) for psoriasis; tender and swollen joint counts, CRP,ESR] HAQ (health assessment questionnaire), Dermatology Life Quality Index (DLQI), Bristol Rheumatoid Arthritis Fatigue Numeric Rating Scale (BRAF-NRS) and SF-36. Radiographs were taken of involved joints along with hands, feet and sacroiliac joints. AM was considered present when there was one or more shortened digit accompanied on radiographs by osteolysis or erosions on both sides of the joint. 

Results: A total of 283 PsA patients [mean age 55±12 years; 47% male; mean PsA duration=19±9 years; 25% with sacroiliitis; 44.5% with radiographic erosions; 34% with enthesitis; 53% with dactylitis; 79% with psoriatic nail disease, 60% of this PsA cohort requiring TNFi therapy] were studied. Among this cohort, 8% (n=23) of patients were found to have AM, with 65% female and a mean age of 56.5±11 years. On univariate analysis, longer PsA duration (OR 1.06, p=<0.001), longer diagnostic delay (OR 1.10, p=0.01), more tender joint counts (OR 1.07, p=0.009), more swollen joint counts (OR 1.09, p=0.009), PsA requiring TNFi (OR 3.37, p=0.03), oral corticosteroids usage (OR 9.2, p=<0.001), earlier PsA age of onset (OR 0.96, p=0.08), lower CRP maximum (OR 0.98, p=0.07), lower ESR maximum (OR 0.98, p=0.13) and higher HAQ score (OR 1.07, p=0.10), MCS-SF36 (OR 1.02, p=0.16) and PCS-SF36 (OR 1.00, p=0.80). Given the small number of AM patients, few models were tested on multivariate regression analysis, but it was noted that heavier alcohol intake (OR 1.08, p=0.002), lower CRP rise (0.96, p=0.007), greater oral corticosteroids usage (OR 7.6, p=0.003) and longer duration of PsA (OR 1.08, p=0.001) all remained significantly associated with the diagnosis of AM.

Conclusion: The clinical profile of patients with AM when compared to other PsA patients suggests that non-inflammatory pathogenic mechanisms, possibly related to bone turnover, may explain this unique clinical phenotype.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/clinical-phenotype-of-patients-with-arthritis-mutilans-has-important-differences-compared-to-other-patients-with-psoriatic-arthritis/