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Objective: To investigate the clinical, histological, and immunological features of patients with myasthenia gravis (MG) who also developed myocarditis and/or myositis. Design: Observational and retrospective case series. Setting: Keio University, Hanamaki General Hospital, Kanazawa University, Nagasaki University, and Juntendo University. Patients: A cohort of 8 patients with MG with clinically defined inflammatory myopathies. Interventions: Clinical and histological features were described. Serological analyses included MG-related antistriational autoantibodies (those to titin, ryanodine receptor, muscular voltage-gated potassium channel Kv1.4) and myositis-specific autoantibodies. Results: Of 924 patients with MG, 8 (0.9%) had inflammatory myopathies. The mean (SD) onset age ofMGwas 55.3(10.3) years. All patients showed severe symptoms with bulbar involvement; 5 patients had myasthenic crisis and 4 had invasive thymoma. Myocarditis was found in 3 patients and myositis in 6. Myocarditis, developing 13 to 211 months after the MG onset, was characterized by heart failure and arrhythmias. Myositis, developing before or at the same time as MG, affected limb and paraspinal muscles. Histological findings of skeletal muscles showed CD8+ lymphocyte infiltration. Seven patients had 1 of these antistriational autoantibodies but not myositisspecific autoantibodies. Immunomodulatory therapy was required for all patients and was effective for both MG and inflammatory myopathies, although 1 patient died. Conclusions: Heart and skeletal muscles are autoimmune targets in some patients with MG. This autoimmunity has a broad clinical spectrum with antistriational autoantibodies. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the autoantibody status of patients with myasthenia gravis (MG) and to evaluate its usefulness for disease classification. Design: Retrospective cohort study of patients with MG, who have autoantibodies to receptors and ion channels expressed at neuromuscular junctions and in muscles that impair neuromuscular transmission. One of the autoantibodies studied was a recently identified, novel, MG specific autoantibody to a voltage-gated potassium (Kv) channel, Kv1.4. Setting: Keio University Hospital, Tokyo, and Iwate Medical University Hospital, Morioka. Patients: Two hundred nine patients with MG. Main Outcome Measures: Anti-Kv1.4 antibody was measured by an immunoprecipitation assay with sulfur 35-labeled extract from rhabdomyosarcoma cells. Antititin antibody was detected with a commercially available enzyme-linked immunosorbent assay. Results: Anti-acetylcholine receptor, anti-Kv1.4, and antititin antibodies were detected in 150 (72%), 26 (12%), and 50 (24%) of the 209 patients with MG, respectively. All of the patients who were positive for anti-Kv1.4 or antititin antibody were seropositive for the anti-acetylcholine receptor antibody. They were classified into 4 groups based on their status in regard to 3 MGrelated autoantibodies: anti-Kv1.4, antititin, and anti-acetylcholine receptor. Clinical associations were found between anti-Kv1.4 and bulbar involvement, myasthenic crisis, thymoma, and concomitant myocarditis and/or myositis; between antititin and older-onset MG; between anti-acetylcholine receptor alone and younger-onset MG; and between seronegativity and ocular MG. In addition, patients with MG in the anti-Kv1.4 group had more severe manifestations of disease than those in the other 3 groups. Conclusion: Classification of patients with MG based on autoantibody status may be useful in defining clinical subsets. [ABSTRACT FROM AUTHOR]