Background The PM/Scl autoantigen, which is currently known as the 'human exosome', is a macromolecular complex that consist of up to 16 proteins located primarily in the nucleolus and is involved in RNA processing and degradation. It has 2 major antigenic determinants called PM/Scl-100 and PM/Scl-75 based on their molecular weights. Anti-PM/Scl antibodies were initially reported in patients with systemic sclerosis (SSc)-polymyositis (PM) overlap syndromes but they are associated with a wide variety of autoimmune diseases including isolated SSc, PM, dermatomyositis (DM) and interstitial lung disease (ILD), and less frequently with systemic lupus erythematosus, primary Sjögren's syndrome (pSS) and undifferentiated connective tissue disease (UCTD).
Objectives To describe the clinical and immunological features of PM/Scl-positive patients treated in a Spanish tertiary center.
Methods We performed a retrospective study of patients with PM/Scl-100 and PM/Scl-75 positive antibodies seen in our center during the period 2007–2015. Positivity for these antibodies was detected by line immunoassay and confirmed by indirect immunofluorescence. Demographic and clinical data were obtained through review of their medical records.
Results 17 anti-PM/Scl-positive patients were found during the study period, 12 of them women (70.6%) with a mean age at diagnosis of 57.5 years (range: 38–82). Positivity PM/Scl-75 was detected in 8 cases, for PM/Scl-100 in 4 cases and simultaneously for both antibodies in 5 cases. The diagnoses of these patients were: limited cutaneous SSc in 3 cases, SSc-PM overlap 2, SSc-DM overlap 1, isolated PM 1, isolated DM 1, unspecified myositis 3, isolated ILD 2, pSS 1, UCTD 1 and mitochondrial myopathy 1. The most common clinical manifestations were dyspnea (41.2%), Raynaud's phenomenon (RP) (35.2%), muscle weakness (29.4%), hand edema (23.5%) and arthralgia (23.5%). Three patients developed digital ulcers, 2 'mechanic's hands' and Gottron's papules and 1 calcinosis. No differences in clinical manifestations between PM/Scl-75 and PM/Scl-100 were found. ILD was diagnosed in 8 cases (47.1%) with radiological pattern of usual interstitial pneumonia in 2 cases, nonspecific interstitial pneumonia 2, organizing pneumonia 1, lymphocytic interstitial pneumonia 1 and no characteristic pattern 2. The acute phase reactants (erythrosedimentation rate, C-reactive protein) were elevated in 58.8% and muscle enzymes in 41.2% (creatine kinase mean value 658 IU/L, range: 184–1758), 4 cases had lymphopenia and 6 hypergammaglobulinemia. The antinuclear antibodies were positive in 13 patients, anti-Ro/SSA in 4 and anti-centromere, anti-SRP, and anti-Ku in 1 case each. None of the patients died or developed malignancy (mean follow-up: 70.6 months).
Conclusions The patients in our series presented a heterogeneous clinical profile similar to other series in the literature and the most common manifestations were ILD, RP and myositis. Anti-PM/Scl antibodies have been traditionally associated with overlap syndromes, but we found a wide variety of diagnoses in our cases. Despite the high incidence of ILD in anti-PM/Scl-positive patients, the presence of these antibodies seems to be associated with good prognosis and infrequent development of malignancies.
Disclosure of Interest None declared