Background Although muscle pain is relatively frequent in primary Sjogren Syndrome (pSS), a frank myositis is rare and reported only in 2.5-11% of patients. The most frequent symptoms are muscular weakness and myalgias and diagnosis is based on clinical, laboratory and histologic evaluation.

Objectives To describe the prevalence and course of myositis in a multicenter cohort of patients with pSS.

Methods Clinical and laboratory data from patients with a diagnosis of pSS were retrospectively collected. The clinical charts of patients with symptoms and/or signs of inflammatory myositis were carefully reviewed.

Results One thousand one hundred seventy patients with pSS (52M, 1118 F, mean age 57.3 years; range 17–89 years) were considered. Mean age at diagnosis was 51±14 years and the mean follow up from diagnosis was 5.6 years (range 0–42 years). Ten female patients (0.85%) presented invalidating muscular weakness in the upper and lower limbs and/or severe myalgias. In 8/10 patients an increase of Creatine Phosphokinase (CK) serum level was present. A possible iatrogenic effect was excluded; in one case myositis started under statin therapy but didn’t disappear after drug discontinuation. In the 10 patients, mean age at pSS diagnosis was 47.4 years (range 14–68), while mean age of myositis diagnosis was 50.6 years (range 23–69). In six out of ten, muscular and sicca symptoms had occurred together at onset. Diagnosis of myositis was supported by clinical evidences and by the presence of increased CK serum levels. In 7/10 patients muscle biopsy was performed. In all biopsies signs of inflammation were present. In 1/7 patients (14.2%) the biopsy was typical of an inclusion body myositis, while in the remaining cases histological aspects of Dermatomyositis and Polymyositis (PM) were detected. Eight out of ten patients presented at least three criteria for inflammatory myopathy (according to Bohan and Peter criteria, 1975) suggesting a possible diagnosis of a true overlap syndrome. In one of these patients serum anti Jo-1 and anti RNP antibodies were detected. Six patients (60%) were successfully treated with DMARDs, while four (40%) did not respond. Thus, two were treated with IvIg, one showing complete remission of myositis, and the remaining two non-responder patients were treated with Rituximab, one showing complete remission.

Conclusions Our retrospective study shows a lower prevalence of myositis in pSS than previously reported. Muscle involvement can occasionally represent the first symptom at disease onset. An overlap syndrome with inflammatory myopathies, above all PM, should be considered. Different therapeutic approaches can be used: DMARDs are effective in the majority of the patients, while IvIg and Rituximab may represent an available alternative therapeutic options in non-responder patients.

Disclosure of Interest None Declared