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Benign Clozapine Fever vs Myocarditis — MRCPsych Paper B MCQ

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HardSchizophrenia & PsychosisBenign Clozapine Fever vs MyocarditisMRCPsych Paper B

On day 19 of clozapine titration, a patient in a medium-secure unit develops a temperature of 39.0°C and a pulse of 118 beats/min. CRP rises from 18 mg/L to 72 mg/L but falls to 41 mg/L the following day. High-sensitivity troponin I remains below the assay's 99th percentile on presentation and 12 hours later. ECG is unchanged from baseline and echocardiography shows normal left-ventricular function. The absolute neutrophil count is normal, and examination, chest radiography, urinalysis and cultures identify no infection. There is no muscle rigidity, altered consciousness or raised creatine kinase, and the fever resolves within 48 hours. What is the most likely diagnosis?

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Correct answer: D — Benign clozapine-related fever

The most likely diagnosis is benign clozapine-related fever. It occurs most often during the first 3 weeks and may be accompanied by tachycardia and a transient inflammatory response. Here, the falling CRP, repeatedly normal high-sensitivity troponin, unchanged ECG, normal ventricular function and rapid resolution strongly oppose myocarditis. A single normal troponin would not have been sufficient, because some myocarditis cases initially lack a significant troponin rise. Pneumonia and urinary infection are unsupported by the clinical assessment and investigations. NMS is unlikely without rigidity, altered mental state, autonomic instability beyond fever-related tachycardia, or raised creatine kinase. Benign fever remains a diagnosis of exclusion and requires continued clinical and biochemical monitoring rather than automatic reassurance.

Reference: Clozapine Viatris 200 mg Tablets, Summary of Product Characteristics, section 4.4: Cardiovascular disorders and Fever, updated 20 April 2026. https://www.medicines.org.uk/emc/product/102058/smpc