IIMs are characterized by non-purulent muscle inflammation and muscle weakness[5]. Subtypes of IIM include polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM), predominantly observed in adults, whereas juvenile dermatomyositis (JDM) is more prevalent among children. ASS is recognized as a subset of PM/DM[6].
The diagnostic criteria for IIMs, established by Bohan and Peter, are widely employed in clinical settings[7, 8]. In 2017, the European League Against Rheumatism (EULAR) and the American College of Rheumatology (ACR) introduced more stringent and clinically pertinent revised classification and diagnostic criteria for IIMs in adults and adolescents[6]. ASS was initially described by Marguerie et al. in 1990[9], and its hallmark clinical features are associated with the presence of anti-tRNA synthetase antibodies. Patients with ASS often exhibit a spectrum of clinical and laboratory signs, however, a unified diagnostic standard for ASS has not been established in clinical practice. In 2010, Connor et al. first formally suggested potential diagnostic criteria for ASS[10], followed by more rigorous criteria proposed by Solomon et al. in 2011. The criteria for diagnosis[11] include the presence of an anti-aminoacyl-tRNA synthetase antibody plus two major criteria or one major and two minor criteria. Major criteria include: (1) interstitial lung disease (ILD) not explained by environmental, occupational, or drug exposures and unrelated to any other underlying disease, and (2) polymyositis or dermatomyositis meeting the Bohan & Peter criteria. Minor criteria include: (1) arthritis, (2) Raynaud’s phenomenon, (3) mechanic’s hands. While arthritis, mechanic's hands, and Raynaud's phenomenon support the diagnosis, they are not essential for it.
Currently, 20 anti-ARS antibodies have been identified, with 8 being closely associated with ASS, including anti-Jo-1 (histidyl-tRNA synthetase), the first to be discovered and characterized[12]; anti-PL-7 (threonyl); anti-PL-12 (alanyl); anti-EJ (glycyl); anti-OJ (isoleucyl); anti-KS (asparaginyl); anti-Zo (phenylalanyl); and anti-Ha (tyrosyl)[13, 14]. Anti-PL-7 is among the rarest.
Studies in Japan and France have demonstrated that all patients with anti-PL-7 positive ASS exhibit concurrent ILD, with myositis occurring in approximately 50–86% of cases[15–17]. Labirua-Iturburu et al.'s comprehensive study indicated that the most common presentations of PL-7 antibody-positive ASS were interstitial lung disease (77.8%), myositis (75%), and arthritis (56%)[18]. Additional research suggests that patients with anti-PL-7 or anti-PL-12 antibodies typically experience more severe ILD, while myositis is less frequent[19]. A meta-analysis of 27 studies on ASS found that joint pain and ILD were predominant, with myositis being less common among patients with anti-PL-7 or anti-PL-12 antibodies compared to those with anti-Jo-1 antibodies[20].
The patient initially presented with fever, followed by myalgia and Gottron's papules. Serum creatine kinase levels were significantly elevated, and a chest CT revealed interstitial changes. Positive anti-PL-7 antibodies were detected via the myositis antibody spectrum test. Diagnosis of antisynthetase syndrome was confirmed through muscle MRI and biopsy results. Given the scarcity of reported PL-7 positive ASS cases in children, differences in clinical manifestations, signs, or laboratory tests between children and adults remain unclear. The patient's characteristics align with those reported in existing literature, although fever as an initial symptom is atypical for previously reported cases. Earlier studies suggest that patients with non-Jo-1 positive ASS often exhibit earlier onset and more severe ILD, leading to poor prognosis and reduced survival rates. This patient did not display typical clinical manifestations of ILD, such as cough, chest pain, fatigue, or breathing difficulties, and no significant positive signs were observed in the lungs. However, interstitial changes were noted on chest CT. Consequently, ongoing treatment and follow-up are necessary to monitor lung lesions dynamically and enhance long-term prognosis. These observations may be attributed to the brief duration of the disease and follow-up period. Whether there are differences between PL-7 positive ASS cases in children and adults requires additional observation, and further case summaries are needed. Additionally, an independent cohort study identified pericarditis as a potential manifestation linked to anti-PL-7 antibodies[18], necessitating dynamic monitoring via cardiac ultrasound during later follow-up stages.
Currently, the preferred treatment for antisynthetase syndrome is hormonal therapy[21], with monthly dosage reductions to achieve the minimal effective dose for improving muscle function. Hormone therapy should continue for at least 2 years. For patients presenting with severe symptoms, high-dose corticosteroids remain the first-line treatment to mitigate inflammation. Concurrent treatment with methotrexate and mycophenolate mofetil may be adjusted based on the patient's condition. Rituximab and other biologic agents may be considered for refractory cases. The child has been treated with steroids and methotrexate, resulting in well-controlled symptoms. Upon re-examination, creatine kinase levels had normalized.