P222 Clinical features of extra-muscular disease in dermatomyositis and anti-synthetase syndrome patients with skin involvement classified by presence of disease-specific autoantibodies: results from the EuroMyositis registry
Authors: Hum Ryan M , Lilleker James B , Lamb Janine A , Ollier William E , Wang Guochung , Wedderburn Lucy R , Diederichsen Louise P , Schmidt Jens , Oakley Paula , Benveniste Olivier , Danieli Maria G , Danko Katalin , Thuy Nguyen T. P , Mercado Monica V. D , Andersson Helena , Paepe Boel D , Bleecker Jan L. D , Maurer Britta , McCann Liza J , Pipitone Nicolo , McHugh Neil , New Paul , Vencovsky Jiri , Lundberg Ingrid E , Chinoy Hector 
Published: April 2022

Abstract

Background/Aims
Anti-synthetase syndrome (ASS) represents a distinct entity within myositis spectrum disorders; however, correct classification of patients with anti-tRNA synthetase autoantibodies and skin manifestations akin to dermatomyositis (DM) remains uncertain. Our aim was to compare clinical characteristics, skin involvement, and malignancy, between patients with ASS and DM, classified by disease-specific autoantibodies.

Methods
Data from 05/2009-03/2016 from 9 countries from the prospective, myositis EuroMyositis registry were downloaded. Those with anti-tRNA synthetase autoantibodies (Jo-1/PL-7/PL-12/OJ/EJ/KS) were classified as ASS, and those with Mi-2/TIF1-γ/NXP2/SAE/MDA5 autoantibodies as DM. Clinical phenotypes including malignancies (except skin malignancies) were tabulated. Characteristics of patients with skin involvement (excluding mechanic’s hands and Raynaud’s phenomenon) were compared using Fisher’s exact test with Bonferroni corrected p-values.

Results
Of 3,067 patients, 2,028 had autoantibody profiling results (66.1%), of which 783 (38.6%) were positive for at least one of the autoantibodies being considered. Five patients with dual autoantibody specificities were excluded. Of the remaining 778, 320 (41.1%) were classified as DM, and 458 (58.9%) as ASS. Median age at diagnosis was 48.2 years (interquartile range [IQR] 37.5 to 57.8) in the DM cohort and 49 (IQR 38.3 to 62.2) in the ASS cohort. Skin involvement was present in 277 (86.6%) DM patients (DM skin) vs 204 (44.5%) ASS patients (ASS skin) (pcorr&lt;0.01) (Table 1). Whilst relatively high proportions of so-called “DM-specific” rashes were seen in ASS skin, the frequency of heliotrope rash, Gottron’s papules, violaceous rash, periorbital rash, V-sign, shawl sign, and periungual erythema was significantly higher in DM skin (pcorr&lt;0.01 for all). Conversely, mechanic’s hands, Raynaud’s, arthritis, and interstitial lung disease were more frequent in ASS skin (pcorr&lt;0.01 for all). Malignancy was less frequent in ASS skin vs DM skin (pcorr&lt;0.01) and occurred temporally closer to myositis diagnosis in DM skin (median 0.95 months [IQR -6.54. to 19.45]) vs ASS skin (median 12.17 months [IQR -15.85 to 79.31]).

Conclusion
Patients with ASS have frequent skin involvement but also a distinct clinical phenotype compared to DM. These findings may inform the development of future classification criteria for ASS.

Disclosure
R.M. Hum: None. J.B. Lilleker: None. J.A. Lamb: None. W.E. Ollier: None. G. Wang: None. L.R. Wedderburn: None. L.P. Diederichsen: None. J. Schmidt: None. P. Oakley: None. O. Benveniste: None. M.G. Danieli: None. K. Danko: None. N.T.P. Thuy: None. M.V.D. Mercado: None. H. Andersson: None. B.D. Paepe: None. J.L.D. Bleecker: None. B. Maurer: None. L.J. McCann: None. N. Pipitone: None. N. McHugh: None. P. New: None. J. Vencovsky: None. I.E. Lundberg: None. H. Chinoy: None.