PT  - JOURNAL ARTICLE
AU  - Naohiro Uchio
AU  - Kenichiro Taira
AU  - Chiseko Ikenaga
AU  - Masato Kadoya
AU  - Atsushi Unuma
AU  - Kenji Yoshida
AU  - Setsu Nakatani-Enomoto
AU  - Yuki Hatanaka
AU  - Yasuhisa Sakurai
AU  - Yasushi Shiio
AU  - Kenichi Kaida
AU  - Akatsuki Kubota
AU  - Tatsushi Toda
AU  - Jun Shimizu
TI  - Inflammatory myopathy with myasthenia gravis
AID  - 10.1212/NXI.0000000000000535
DP  - 2019 Mar 01
TA  - Neurology - Neuroimmunology Neuroinflammation
PG  - e535
VI  - 6
IP  - 2
4099  - http://nn.neurology.org/content/6/2/e535.short
4100  - http://nn.neurology.org/content/6/2/e535.full
SO  - Neurol Neuroimmunol Neuroinflamm2019 Mar 01; 6
AB  - Objective To provide evidence that idiopathic inflammatory myopathy (IM) with myasthenia gravis (MG) frequently shows thymoma association and polymyositis (PM) pathology and shares clinicopathologic characteristics with IM induced by immune checkpoint inhibitors (ICIs).Methods We analyzed the clinicopathologic features of 10 patients with idiopathic IM and MG identified in 970 consecutive patients with biopsy-proven IM.Results Seven patients (70%) had thymoma. IM and MG were diagnosed with more than 5-year time difference in 6 thymomatous patients and within 1 year in 1 thymomatous and 3 nonthymomatous patients. Seven thymomatous patients showed rhabdomyolysis-like features with respiratory failure (4/7), dropped head (3/7), cardiac involvement (2/7), and positive anti–acetylcholine receptor (anti-AChR) and anti-titin antibodies (7/7 and 4/6, respectively) but rarely showed ocular symptoms (2/7) or decremental repetitive nerve stimulation (RNS) responses (1/7) at IM diagnosis. Three nonthymomatous patients showed acute cardiorespiratory failure with rhabdomyolysis-like features (1/3), positive anti-AChR and anti-titin antibodies (3/2 and 2/2, respectively), and fluctuating weakness of the skeletal muscle without ocular symptoms (3/3). Muscle pathology showed a PM pathology with infiltration of CD8-positive CD45RA-negative T-lymphocytes (9/9), scattered endomysial programmed cell death 1 (PD-1)–positive cells (9/9), and overexpression of programmed cell death ligand 1 (PD-L1) on the sarcolemma of muscle fibers around the infiltrating PD-1–positive cells (7/9).Conclusion Rhabdomyolysis-like features, positive anti-AChR antibody without decremental RNS responses, and PD-L1 overexpression are possible characteristics shared by ICI-induced IM. Frequent thymoma association in patients with idiopathic IM and MG may suggest thymoma-related immunopathogenic mechanisms, including dysregulation of the immune checkpoint pathway.anti-AChR=anti–acetylcholine receptor; CK=creatine kinase; CTLA-4=cytotoxic T-lymphocyte–associated protein 4; IBM=inclusion body myositis; ICI=immune checkpoint inhibitor; IM=inflammatory myopathy; MG=myasthenia gravis; MHC=major histocompatibility complex; MSA=myositis-specific autoantibody; PD-1=programmed cell death 1; PD-L1=programmed cell death ligand 1; PM=polymyositis; PSL=prednisolone; RNS=repetitive nerve stimulation; SFEMG=single-fiber electromyogram