Background/Purpose: Myositis-specific autoantibodies (MSAs) have been shown to predict clinical features and have prognostic implications in patients with idiopathic inflammatory myopathies (IIMs), with anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5 Ab) and anti-transcriptional intermediary factor antibody (anti-TIF1γAb) being associated with potential life-threatening complications. However, testing of autoantibodies in inflammatory myopathy is not routinely performed in Hong Kong due to its cost and limited availability. The aim of the study is to investigate the prevalence of MSAs and their associated complications.

Methods: A total of 201 consecutive patients with IIMs being followed up in the Rheumatology clinics of participating regional hospitals from July 2016 to January 2018 were recruited. Clinical characteristics, treatment history and disease complications such as interstitial lung disease (ILD), rapidly progressive interstitial lung disease (RP-ILD) and malignancies were documented. Immunoblot assay was used to detect the presence of MSAs in all the participants.

Results: Out of the 201 patients with IIMs, 122 (60.7%) had dermatomyositis while 79 (39.3%) had polymyositis. Around 63.2% patients had at least one MSA positive. The most common MSAs were anti-MDA5 Ab (28, 13.9%) and anti-TIF1γ Ab (28, 13.9%), followed by anti-Jo-1 Ab (25, 12.4%). Anti-MDA5 Ab was present exclusively in dermatomyositis and was strongly associated with digital ulcers, clinically amyopathic dermatomyositis (CADM) and RP-ILD (all p<0.001). Anti-TIF1γ Ab was strongly associated with refractory rash and malignancy (both p<0.001). Anti-Jo-1 Ab was strongly associated with interstitial lung disease (ILD) (p=0.001) and was negatively associated with malignancy (p=0.006). Multivariate analysis showed that independent risk factors of development of RP-ILD included anti-MDA5 Ab positivity (OR 14.5, p=0.001), CADM (OR 13.9, p=0.015) and history of pulmonary tuberculosis (OR 12.2, p=0.026). By Cox regression with adjustment of confounders, independent risk factors for malignancy included anti-TIF1γ Ab positivity (HR 3.55, p=0.002), dermatomyositis (HR 3.82, p=0.009) and family history of cancer (HR 3.40, p=0.038). In 45 newly diagnosed IIM patients, 32 (71.1%) had dermatomyositis and 13 (28.9%) had polymyositis. Kaplan Meier analysis showed that the 6-month mortality in patients with anti-MDA5 Ab was 47.5%, compared to 11.1% in those without anti-MDA5 Ab. Anti-MDA5 was associated with significantly lower survival (p=0.002).

Conclusion: The local data on MSA profiles and their clinical associations were established. Anti-MDA5 Ab was associated with CADM, RP-ILD and poorer survival, while anti-TIF1γ Ab was associated with malignancy in Hong Kong Chinese patients with IIMs, especially nasopharyngeal carcinoma. MSA testing enables early confirmation of these diseases with potentially life-threatening complications, and will have an important impact on the management of pulmonary disease and vigilance of malignancy screening.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/myositis-specific-autoantibodies-and-their-clinical-associations/