Myositis in primary Sjögren's syndrome: data from a multicentre cohort

In primary Sjögren's syndrome (pSS), muscle pain and/or muscular weakness is relatively frequent while myositis has been reported in 3% of patients. The aim of this study was to describe the prevalence of myositis in a multicentre Italian pSS cohort and to address the clinical manifestations, histological findings and therapeutic strategies.

Clinical, serological and therapeutic data from a pSS cohort of patients were retrospectively collected. According to Bohan and Peter's criteria, inflammatory myopathy (IM) was suspected in case of muscular weakness associated with increased creatine-phosphokinase (CPK) or abnormal electromyography (EMG). When performed, muscle biopsies were analysed.

In a cohort of 1320 patients, 17 (1.28%) presented muscular weakness [in some cases myalgias (7/17, 41.1%)], accompanied by increased CPK [13/17, (76.4%)] and/or abnormal EMG [13/14, (92.8%)]. Ten out of 17 (58.8%) fulfilled at least three diagnostic criteria for IM. Muscular biopsy was performed in 13/17 (76.4%) cases with histologically confirmed myositis in 6/13 (46.1%) (1"IBM-like"-5"PM-like"). In two "PM-like" cases, several fibres showed a decreased histochemical cytochrome C oxidase (COX) stain. Two biopsies tested "negative", four showed "non-specific" findings. All patients were treated with corticosteroids followed by different DMARDs.

Our retrospective analysis shows a prevalence of myositis in pSS lower than previously reported, mainly appearing as an overlapping syndrome. Histological findings confirm the possible presence of an IBM or of a myopathy more similar to PM with a decreased COX activity. Classical immunosuppressants are effective although in most difficult cases IVIg or RTX may be used with benefit.