Clinical characteristics of myositis patients with isolated anti-U1 ribonucleoprotein antibody resemble immune-mediated necrotizing myopathy

Yongpeng Ge; Hongxia Yang; Wei Jiang; Xiaolan Tian; Xin Lu; Guochun Wang

doi:10.1177/1759720X231181336

Clinical characteristics of myositis patients with isolated anti-U1 ribonucleoprotein antibody resemble immune-mediated necrotizing myopathy

Ther Adv Musculoskelet Dis. 2023 Jul 14:15:1759720X231181336. doi: 10.1177/1759720X231181336. eCollection 2023.

Authors

Yongpeng Ge¹, Hongxia Yang^{1

2}, Wei Jiang¹, Xiaolan Tian¹, Xin Lu¹, Guochun Wang^{3

2}

Affiliations

¹ Department of Rheumatology, The Key Laboratory of Myositis, China-Japan Friendship Hospital, Beijing, China.
² Peking University China-Japan Friendship School of Clinical Medicine, Beijing, China.
³ Department of Rheumatology, The Key Laboratory of Myositis, China-Japan Friendship Hospital, Yinghua East Road, Chaoyang District, Beijing 100029, China.

Abstract

Background: Anti-U1 ribonucleoprotein (U1RNP) antibodies were associated with connective tissue diseases (CTDs), but the clinical characteristics of this antibody in Chinese myositis patients have not been studied.

Objective: We aim to analyze the clinical features of myositis patients who test positive for anti-U1RNP antibodies and delineate a subgroup of myositis.

Design: This is a retrospective cohort study.

Methods: We reviewed the clinical data of myositis patients with anti-U1RNP antibodies and compared them to those with anti-signal recognition particle (SRP) and hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibody-associated immune-mediated necrotizing myopathy (IMNM).

Results: A total of 30 adult cases were identified; median age was 47.5 years and 24 (80%) were females, and 12 patients did not coexist with myositis-specific antibodies (MSAs) (isolated anti-U1RNP). The serum creatine kinase (CK) was significantly higher in patients with isolated anti-U1RNP (2182.5 U/L versus 289 U/L, p = 0.01), and the number of patients with CK > 2000 U/L was higher compared to that in anti-U1RNP antibody patients coexisting with MSAs (66.7% versus 16.7%, p = 0.009). The prevalence of IMNM in patients' muscle pathology with isolated anti-U1RNP was significantly higher (75%, p = 0.003). Skin rashes were less common in isolated anti-U1RNP group (p < 0.05). Of the 25 individuals with available pulmonary high-resolution CT (HRCT), 14 (56%) were diagnosed with interstitial lung disease (ILD). The incidence of muscular weakness, dysphagia, or levels of CK was not different between the isolated anti-U1RNP antibody individuals and the anti-HMGCR or SRP-IMNM groups (p > 0.05). But the frequency of Raynaud's phenomenon, arthritis, and membrane attack complex (MAC) deposits in myositis patients with isolated anti-U1RNP antibodies were higher than in anti-HMGCR and SRP-IMNM (all p < 0.005). There was no difference between anti-U1RNP patients with and without Ro-52 (p > 0.05). Isolated anti-U1RNP individuals showed marked improvements in muscle strength, and the remission rate in 1 and 2 years was significantly higher than that in anti-HMGCR and SRP-IMNM (p < 0.05).

Conclusions: The clinical and pathological features of myositis patients with isolated anti-U1RNP antibodies were similar to IMNM. Arthritis and ILD are the most common extramuscular clinical features. Most respond well to treatment and have a good prognosis.

Keywords: anti-U1RNP antibody; anti-hydroxy-3-methylglutaryl-CoA reductase antibody; anti-signal recognition particle antibody; immune-mediated necrotizing myopathy; myositis.