Mesalazine-Induced Myocarditis Following Dose Escalation in Ulcerative Colitis: A Diagnostic Challenge.

Introduction: Mesalazine (5-aminosalicylic acid, 5-ASA) is the cornerstone treatment for mild-to-moderate ulcerative colitis. Although generally well tolerated, rare cases of drug-induced myocarditis have been reported. Distinguishing mesalazine-induced myocarditis from myocarditis related to inflammatory bowel disease is essential, as management differs substantially. Case description: A 43-year-old man with recently diagnosed ulcerative colitis presented with acute chest pain, fever and elevated cardiac biomarkers eight days after initiation of oral mesalazine (3 g/day). Electrocardiography demonstrated diffuse ST-segment elevation, while echocardiography showed preserved left ventricular systolic function; coronary angiography excluded obstructive coronary artery disease. During hospitalisation, worsening gastrointestinal symptoms prompted escalation of mesalazine to 4.8 g/day. Within 24 hours, the patient developed recurrent chest pain, fever and a marked increase in troponin, inflammatory markers and NT-proBNP. Viral and autoimmune investigations were negative. The close temporal relationship between symptom recurrence and dose escalation raised suspicion of mesalazine-induced myocarditis. Following discontinuation of mesalazine, rapid clinical and biochemical improvement was observed. A cardiac magnetic resonance imaging (MRI) performed on day 7 demonstrated myocardial oedema on T2-weighted sequences and non-ischaemic epicardial late gadolinium enhancement involving the apical and inferolateral segments. This fulfilled both T2-based and T1-based criteria of the 2018 modified Lake Louise criteria for acute myocarditis. At follow-up, the patient remained asymptomatic with complete recovery of ventricular function. Conclusion: Mesalazine-induced myocarditis is an uncommon but potentially serious adverse reaction that may mimic an extraintestinal manifestation of ulcerative colitis. Early recognition, careful assessment of drug exposure chronology and prompt withdrawal of mesalazine are crucial to prevent complications. Cardiac MRI plays a central role in confirming the diagnosis. LEARNING POINTS: Mesalazine-induced myocarditis is a rare but potentially life-threatening adverse effect that should be suspected in any patient with inflammatory bowel disease presenting with chest pain shortly after treatment initiation or dose escalation.Differentiating drug-induced myocarditis from myocarditis related to inflammatory bowel disease is crucial, as continuation of mesalazine may worsen cardiac injury.Prompt withdrawal of mesalazine usually leads to complete clinical recovery, while cardiac MRI plays a key role in confirming the diagnosis.