Background and Objectives Arthritis in idiopathic inflammatory myopathies (IIM) is frequently observed in clinical practise, but, to our knowledge, there is lack of systemic reports of prevalence and/or characteristics of arthritis in myositis patients. The aim of this study is to determine prevalence of arthritis in IIM patients; it’s relation to the course of the muscle disease; characteristics of arthritis with respect to seriousness, distribution and extent as well as it’s relation to autoantibody profiles and others disease’s characteristics.
Materials and Methods In this cross-sectional study, clinical aspects of disease, history of arthritis and autoantibody profiles were obtained from 106 consecutive patients with definite diagnosis of IIM. In all of them the 68-joint index was investigated. In 55 IIM patients and in 60 control patients with rheumatoid arthritis (RA) German Ultrasound Score 7 (US-7) was performed.
Results Arthritis at any time of course of myositis occurred in 65 patients (61.3%); 42 had arthritis at the beginning of myositis (in 22 patients before and in 16 together with onset of muscle weakness). 52 patients presented arthritis at clinical examination (25 poly-, 17 oligo-, and 10 with monoarthritis). Most frequently affected joints were wrists (21.7%) and shoulders, metacarpophalangeal, and proximal interphalangeal joints (20.8%). From 29 anti-Jo-1 positive patients 28 had arthritis and significant association between arthritis and anti-Jo-1 positivity was found (p < 0.0001). 39 out of 55 (70.9%) patients had Gray-Scale (GS) synovitis on ultrasound; in 34 of them also Power-Doppler (PD) positivity was found. Only 4 patients had ultrasonographic tenosynovitis and 3 had bony erosions. From 60 RA patients 57 (95%) had GS synovitis, which was PD-active in 54. Tenosynovitis was found in 25 patients. 25 RA patients had one or more joint erosions. Mean US-7 score as well as scores of individual joints or modality subscores were significantly lower in IIM than in RA, but, when compared only those patients with positive findings, the differences were found in total US-7 score, and GS-synovitis and PD-tenosynovitis subscores, but not in PD-synovitis, GS-tenosynovitis as well as in scores of individual joints.
Conclusions Our data suggest that arthritis is common feature of myositis. It is often present at the beginning of muscular manifestation of disease, or it even precedes the onset of muscle weakness. Most common presentation is symmetrical, non erosive polyarthritis affecting particularly wrists, shoulders, metacarpophalangeal and proximal interphalangeal joints of the hands. We confirmed strong association of arthritis with anti-Jo-1 antibody. Ultrasound investigation of joint involvement in IIM shows less frequent involvement than in RA, but comparable activity of synovitis measured by PD in affected joints. IIMs have less erosions and tenosynovitis than RA.