Background: The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of conditions characterized by proximal muscle weakness. Autoantibodies are identified in more than 80% of patients with polymyositis (PM) or dermatomyositis (DM). Some are also found in other connective tissue diseases (CTD), while others are more specific to IIM. Thus, they are classified into two categories named myositis associated antibodies (MAA) and myositis specific antibodies (MSA). MSA have been reported as being 90% specific for IIM while MAA are found in up to 50% of myositis patients. ¹

Objectives: The aim of the study was to evaluate the myositis antibody prevalence and to assess the associations of these antibodies with clinical manifestations, final diagnosis, medication received and outcomes.

Methods: A retrospective chart review study was conducted at St. James’s Hospital from 2015-2020. All positive myositis panels were obtained. The MAA evaluated were PMScl (100/75), U1snRNP, Ku and Ro52, while MSA were Mi2a, Mi2b, TIF1, MDA5, NXP2, SAE1, Jo-1, SRP, PL-7, PL-12, EJ and OJ.

Results: We identified 52 patients who were positive for one or more MSA/MAAs. The mean age was 58.9 years, the majority were female (65.3%).The most prevalent MAA was anti-Ro52 (29/52) followed by anti-PMScl 100/75 (7/52), anti-Ku and anti-U1RNP were seen in (3/52) each. The prevalence of MSA were (4/52) for anti-PL12 and (3/52) for anti-SAE1 followed by (2/52) for each of anti-Mi2b, anti-NXP2, anti-Jo, anti-SRP, anti-PL7, anti-EJ and anti-OJ while only (1/52) for anti-MDA5. The most common observed clinical phenotypes in our cohort were arthralgia (20/52), ILD (18/52) and cutaneous manifestations (15/52). Less than a quarter of the studied population had arthritis (8/52), myositis (7/52), raynauds (7/52) and malignancy (4/52). Various diagnosis were allocated for these patients, while only eight cases were diagnosed with dermatomyositis. Medication received and the final outcome for those with strong positive MSA were summarized in table1.

Conclusion: IIM was the final diagnosis in only 15% of positive myositis panels and the presence of antisynthetase antibodies didn’t necessarily indicate the presence of antisynthetase syndrome thus signifying low specificity in our cohort.

REFERENCES:

[1]Ghirardello A, Borella E, Beggio M, Franceschini F, Fredi M, Doria A. Myositis autoantibodies and clinical phenotypes. Auto Immun Highlights . 2014;5(3):69-75. Published 2014 Aug 23.

Disclosure of Interests: None declared