Article ID: CJ-22-0346
A 68-year-old man with a history of thymoma was admitted to Kumamoto University Hospital with a complaint of acute general malaise. The patient had bradycardia with complete atrioventricular block, so an emergency temporary pacemaker was inserted. Endomyocardial biopsy indicated myocarditis. Thereafter, respiratory failure rapidly appeared, and additional laboratory test results showed positive serum anti-acetylcholine receptor antibodies, anti-muscle-specific tyrosine kinase antibodies, and anti-striated muscle antibodies (anti-titin and anti-Kv1.4 antibodies). The patient was eventually diagnosed with myocarditis due to myasthenia gravis (MG). After the initial treatment, cardiac magnetic resonance imaging (CMR; Ingenia CX, Philips Healthcare) was performed. Multiparametric CMR revealed significant prolongation in native T1 (1,450 ms; normal, 1,230–1,250 ms) and T2 (55.0 ms; normal, 40–45 ms), suggesting diffuse myocardial edema. There was a marked elevation in myocardial extracellular volume fraction (44%; normal, 23–28%), which reflects expansion of the extracellular space in the myocardium. Late gadolinium enhancement (LGE) imaging revealed subepicardial LGE involving the septum and anterior and lateral walls of the left ventricle (Figure). The CMR findings implied the occurrence of prolonged myocardial damage.
(A–C) Multiparametric cardiac magnetic resonance imaging, showing native T1 (A), T2 (B), and extracellular volume (ECV; C) maps, and (D–F) late gadolinium enhancement (LGE; arrows) imaging.
A previous report indicated that 1.2% of patients with MG had symptomatic myocarditis leading to severe cardiac events, which can be fatal.1 Anti-striated muscle antibodies are associated with myocarditis in MG and can be surrogate markers of this condition. A previous study reported that approximately 9% of patients with MG who did not have cardiac symptoms had abnormal findings on CMR, which has been proven to be silent myocarditis in MG;1 however, the LGE pattern of this condition was unknown.
K.T. is a member of Circulation Journal’s Editorial Team. The remaining authors have no conflicts of interest to disclose.
