Comparison of clinical features between patients with anti-synthetase syndrome and dermatomyositis: Results from the MYONET registry

Objectives
To compare clinical characteristics, including the frequency of cutaneous, extramuscular manifestations, and malignancy, between adults with anti-synthetase syndrome (ASyS) and dermatomyositis (DM).

Methods
Using data regarding adults from the MYONET registry, a cohort of DM patients with anti-Mi2/-TIF1ɣ/-NXP2/-SAE/-MDA5 autoantibodies, and a cohort of ASyS patients with anti-tRNA synthetase autoantibodies (anti-Jo1/-PL7/-PL12/-OJ/-EJ/-Zo/-KS) were identified. Patients with DM sine dermatitis or with discordant dual autoantibody specificities were excluded. Sub-cohorts of patients with ASyS with or without skin involvement were defined based on presence of DM-type rashes (heliotrope rash, Gottron’s papules/sign, violaceous rash, shawl sign, V sign, erythroderma, and/or periorbital rash).

Results
In total 1,054 patients were included (DM, n=405; ASyS, n=649). In ASyS cohort, 31% (n=203) had DM-type skin involvement (ASyS-DMskin). A higher frequency of extramuscular manifestations, including Mechanic’s hands, Raynaud’s phenomenon, arthritis, interstitial lung disease, and cardiac involvement differentiated ASyS-DMskin from DM (all p<0.001), whereas higher frequency of any of four DM-type rashes: heliotrope rash (n=248, 61% vs n=90, 44%), violaceous rash (n=166, 41% vs n=57, 9%), V sign (n=124, 31% vs n=28, 4%), and shawl sign (n=133, 33% vs n=18, 3%) differentiated DM from ASyS-DMskin (all p<0.005). Cancer-associated myositis (CAM) was more frequent in DM (n=67, 17%) compared to ASyS (n=21, 3%) and ASyS-DMskin (n=7, 3%) cohorts (both p<0.001).

Conclusion
DM-type rashes are frequent in patients with ASyS; however, distinct clinical manifestations differentiate these patients from classical DM. Skin involvement in ASyS does not necessitate increased malignancy surveillance. These findings will inform future ASyS classification criteria and patient management.