Asymptomatic Clozapine-induced Myocarditis Detected by Biomarker Surveillance: A Case Report

Background: Clozapine-induced myocarditis is an uncommon but potentially serious adverse reaction that usually develops during the early weeks of treatment and may remain clinically silent. Case Presentation: A 65-year-old man with schizophrenia and laryngeal cancer in complete remission was assessed three weeks after clozapine initiation. Routine surveillance identified a cardiac troponin level of 1246 ng/L and a C-reactive protein level of 131 mg/L, although he was afebrile, asymptomatic, and haemodynamically stable. Electrocardiography showed sinus rhythm, while computed tomography pulmonary angiography excluded pulmonary embolism. Echocardiography demonstrated mild left ventricular systolic dysfunction, global hypokinesia, a left ventricular ejection fraction of 45%, and a small pericardial effusion. Coronary angiography showed diffuse atherosclerosis without significant obstructive stenosis. Cardiac magnetic resonance imaging revealed elevated native T1 and T2 mapping values and subepicardial late gadolinium enhancement in the basal lateral wall, supporting acute myocarditis. Clozapine was discontinued, the antipsychotic regimen was adjusted, and heart failure therapy was initiated. Troponin and C-reactive protein levels subsequently decreased to approximately 300 ng/L and 60 mg/L, respectively, and left ventricular systolic function was preserved at follow-up. Conclusion: The temporal relationship with clozapine exposure, exclusion of major competing diagnoses, non-ischaemic cardiac magnetic resonance pattern, biomarker decline, and subsequent preservation of ventricular function supported a diagnosis of probable clozapine-induced myocarditis. Routine biomarker surveillance may facilitate detection before cardiac symptoms develop.