Joint Involvement

As a multisystem disorder, dermatomyositis also affects joints. Arthralgia is an early symptom of DM in about one third of the cases; however, its severity seems to diminish as weakness becomes more prominent [1]. Arthralgia and arthritis are not prominent features of DM patients from the USA [2], but in Japan they are important signs, and are even included as new criteria for diagnosis [3]. According to various clinical studies in a large group of patients with IIMs, arthralgia has been present in between 17% and 47% of cases in Canada [4, 5], 26% in Brazil [6], 28% in UK [7], 29% in the USA [8], 35% in Singapore [9], 45% in Sweden [10], 47% in Bulgaria [11], and 65% in Australia [12]. Joint involvement of the hands, wrists, and ankles is most common in patients with overlap syndrome, and is a feature of so-called “antisynthetase” or “Jo-1 syndrome“ [13]. Arthralgias, arthritis, or both are accompanied by morning stiffness. In the first study by Bohan et al. (1977) of 153 patients with PM/DM, 26% of all groups and 53% of the overlap syndrome had arthralgias [14]. In another series of 105 cases, Tymms and Webb [12] observed that 65% of all IIM patients and 100% of those with overlap syndrome had arthritis. Hochberg et al. [8] have found that 29% of all 76 IIM patients and 67% of those from overlap group had arthralgias or arthritis. In a study by Citera et al. [15], of 29 patients with PM/DM, 27.5% had arthritis.

From studies performed to date, joint involvement was more common in males. The mean age was 30 years and the mean disease duration was 5.3 years. PM patients, especially those with antisynthetase antibodies, frequently develop a nonerosive arthralgia or arthritis. The inflammation involves predominantly small joints, including the proximal interphalangeals, metocarpophalangeals, wrists, elbows, ankles, and knees. The anti-Jo-1 antibody is associated with both a deforming, predominantly nonerosive subluxing arthrop-athy [13], and erosive polyarthritis with soft-tissue calcification [15, 16]. Joint affection precedes the muscle disease [17] or occurs simultaneously [18]. Usually the patients are seronegative, and diagnostic radiographs are normal. The analysis of joint fluid shows normal or minimally elevated leukocyte counts [19]. Synovial biopsy shows some fibrin coating and mild proliferation of the synovial lining cells.