Successful treatment of rheumatoid arthritis complicated by anti-Jo-1 antibody-positive myopathy with abatacept: A case report.

Abatacept (ABT) is effective in the treatment of rheumatoid arthritis (RA).　However, there is no consensus regarding the treatment of patients with RA and idiopathic inflammatory myopathy (IIM).　Here, we describe the case of a 55-year-old Japanese female with a 5-year history of RA who developed anti-Jo1 antibody-positive IIM.　She developed myalgia and dyspnea while receiving a combination therapy of methotrexate and a Janus kinase inhibitor for RA.　Chest computed tomography imaging revealed bilateral middle-to-lower lung frosted shadows.　Magnetic resonance imaging of the lower limbs showed a high short tau inversion recovery signal in the bilateral thigh muscle groups.　Needle electromyography revealed myogenic changes in the proximal muscles of both the upper and lower extremities.　Symmetric proximal muscle weakness, elevated serum muscle enzymes, and the presence of anti-Jo1 antibodies were noted.　The diagnosis of IIM was made according to the European Alliance of Associations for Rheumatology diagnostic criteria.　The myositis symptoms stabilized with glucocorticoids; however, RA worsened during steroid tapering.　After ABT initiation, RA clinical symptoms and functional outcomes improved and myositis remained in remission.　In conclusion, ABT may be an effective treatment option for patients with RA and IIM.　.