Difficulties in diagnosing anti-synthetase syndrome with negative immunological assessment

Abstract

<bold>Introduction:</bold> Anti-synthetase syndrome (ASS) is a subgroup of idiopathic inflammatory myopathies which are a serious autoimmune pathology and could be life-threatening due to lung involvement. <bold>Aims:</bold> Highlighting the difficulties in diagnosing anti-synthetase syndrome with negative immunological assessment. <bold>Methods:</bold> Retrospective study focusing on patients treated for ASS, in the respiratory department. Results A total of 23 patients with ASS were enrolled (mean age=54; gender ratio H/F= 0.35).ASS was diagnosed before ILD in 6. For the 17 other cases, extra thoracic symptoms were reported in 11 cases: polyarthralgia (8/11), palmar-plantar hyperkeratosis (5/11), muscle weakness (3/11). The average value of creatinine phosphokinase (CPK) was 202U/l(16-1200U/l). CT patterns were: UIP(n=3), OP(n=2), NSIP (n=12). In the immunological assessment, the antibodies detected were:anti-PL12 (n=1), anti-EJ (n=1), anti-Ku (n=2), anti-PL7 (n=2), anti-JO1(n=3), anti-OJ(n=5). For the 3 patients with a negative myositis’ panel, antinuclear antibodies were positive in 2 cases with cytoplasmic fluorescence in one case evoquing anti synthetases antibodies. For these 3 patients, the capillaroscopy was pathological in 2 cases and the electromyogram was pathological in the 3 cases.A muscle biopsy was performed in these 3 patients to confirm the diagnosis of SSA. The evolution under corticosteroid therapy and immunosuppressive therapy was towards improvement (n=3), stability(n=5), worsening (n=8), chronic respiratory failure and long-term oxygen therapy (n=6) and death (n=5). <bold>Conclusions:</bold> The ASS diagnosis relies on the myositis panel, with capillaroscopy, electromyography, and muscle biopsy aiding in difficult cases.