A Case of Paraneoplastic Inflammatory Myositis False-positive for Anti-aminoacyl-tRNA synthetase Antibody Successfully Ameliorated by Immunosuppressive Therapy

• Published in: Internal medicine (Tokyo, 1992)
• Main Authors: Akiyama, Masahiro, Arinuma, Yoshiyuki, Nakamura, Yosuke, Utsunomiya, Takaya, Nishigaki, Akisato, Ando, Rufuto, Mizuno, Ryoshin, Mitsui, Asako, Sugitani, Naohiro, Ito, Yuhei, Nakajima, Ayako
• Format: Journal Article
• Language: English
• Published: Japan 07.08.2025
• Subjects: polymyositis; malignancy; myositis-specific antibody; anti-aminoacyl-tRNA synthetase antibodies; paraneoplastic syndrome
• ISSN: 0918-2918; 1349-7235; 1349-7235
• DOI: 10.2169/internalmedicine.5686-25

We herein report a 60-year-old woman with anti-aminoacyl-tRNA synthetase (ARS) antibody-false-positive paraneoplastic polymyositis complicated with ovarian carcinoma, which was promptly ameliorated by immunosuppressive therapy, including glucocorticoids (GCs), before treatment against malignancy. The patient was admitted to our hospital because of rapidly progressive muscular weakness of the neck and both limbs over three weeks. Upon a detailed examination, the patient tested positive for anti-ARS antibodies by an enzyme-linked immunosorbent assay (ELISA), which were later determined to be false positives, as confirmed by immunoblotting and immunoprecipitation. She was strongly suspected to have ovarian carcinoma and pulmonary metastasis. A biopsy of her muscle revealed myositis, mainly with CD68 macrophage infiltration and slightly with CD8 T cells. High-dose GC therapy was introduced as remission induction therapy before intervention for ovarian carcinoma (later revealed as clear cell carcinoma), which showed prompt efficacy for her laboratory findings and then gradually improved her symptoms thereafter. It is speculated that the unusual immunological condition of cancer-associated myositis, characterized by enhanced antibody production, including non-specific autoantibodies such as anti-ARS antibodies, may influence the treatment response. Therefore, a detailed investigation of muscle pathology and the specificity of anti-ARS antibodies could help clarify the precise pathogenesis of inflammatory myositis, even when myositis and anti-ARS antibodies detected by an ELISA are simultaneously detected in patients with malignancy.