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Science News: Muscular and Extramuscular Clinical Features of Patients with Anti-PM/Scl Autoantibodies

Submitted by Leigh Maria K. Ramos-Platt, MD, News Science Editorial Board
Edited by Benn E. Smith, MD, News Science Editorial Board
DeLorenzo, R. et al. Muscular and extramuscular clinical features of patients with anti-PM/Scl autoantibodies. Neurology. 2018 Jun 5;90(23):e2068-e2076. doi: 10.1212/WNL.0000000000005638. Epub 2018 May 4.
In this study, DeLorenzo et al asked the question whether there were features which set anti-PM/Scl autoantibody positive myositis patients apart from those patients with the 3 most common myositis (Dermatomyositis – DM, Antisynthetase Syndrome – AS, and Immune Mediated Necrotizing Myopathy – IMNM). Using data from the John Hopkins Myositis Center Longitudinal Cohort collected between 2002 and 2016, various clinical and diagnostic study parameters found that there were differences which set anti-PM/Scl autoantibody myositis patients apart. 
This study stemmed from the observation that myositis overlaps with other connective tissue disorders. Systemic sclerosis is the most common (40%). Out of 949 patients identified as myositis patients in the Myositis Cohort study, 178 had DM, 132 has AS, 185 had IMNM, and 41 were positive for anti-PM/Scl. 
Key Features that Set Anti-PM/Scl Patients Apart  
1. Muscle weakness was not as prominent early in the course but became more prominent with time 
2. Unlike the 3 most common myositis types, the deltoid was more affected than the hip flexors. In DM, AS, and IMNM, the hip flexors were more affected. 
3. 23% of patients with anti-PM/Scl positive myositis had distal weakness despite the majority not having clinical generalized scleroderma. 
4. Of the 21/41 patients with available muscle biopsy results, 17 had perivascular inflammation.  
5. Perifascicular atrophy was twice as common in DM and AS (56% and 52% respectively) compared to 24% in patients with anti-PM/Scl positive myositis patients’ muscle biopsies. 
6. Thigh muscle edema seen on MRI was more common in DM, AS, and IMNM, compared to anti-PM/Scl patients (71%, 76%, and 90% respectively vs 39%). 
7. Anti-PM/Scl positive patients were more likely to develop pulmonary hypertension (12%) compared to 3% or less in the other 3 disorders. 
8. Patients with anti-PM/Scl were more likely to have or develop skin features such as Gottron rashes, mechanic’s hands, sclerodactyly, Raynaud phenomenon, and telangiectasias.  
9. Patients with anti-PM/Scl antibody positive myositis tended to respond to immunosuppressive therapies quite well. 
Comment: The findings of this study suggest that there are multiple features which set anti-PM/Scl antibody positive myositis apart from DM, AS, and IMNM. This distinction is important when determining overall treatment strategies.  

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