S4960 A Rare and Fatal Case of Mesalamine—Induced Myocarditis

Introduction: Mesalamine is widely regarded as a safe and effective first-line treatment for ulcerative colitis. However, rare but potentially life-threatening adverse effects such as myocarditis must not be overlooked. Case Description/Methods: A 59-year-old woman with a recent diagnosis of ulcerative colitis presented to the emergency department with acute respiratory distress. She had undergone a colonoscopy on February 6, 2024, revealing active chronic colitis with crypt abscesses in the cecum, rectum, and sigmoid colon. Following diagnosis, she was started on mesalamine (Lialda®) 4.8 g daily. Shortly thereafter, she began experiencing upper abdominal discomfort, worsening acid reflux, bloating, fatigue, and exertional shortness of breath. Believing her symptoms were related to the medication, she self-discontinued mesalamine. Despite ongoing symptoms, she remained stable until presenting to our GI clinic with persistent diarrhea, vague abdominal complaints, and progressive dyspnea. Lab results revealed elevated fecal calprotectin (948 mcg/g) and C-reactive protein (6.62 mg/L), with negative infectious stool studies. Due to escalating shortness of breath and fatigue, she was advised to seek emergency care. Upon arrival to the emergency department, the patient was in acute hypoxic respiratory failure with profound metabolic acidosis (pH 6.9, lactate ∼13). She rapidly decompensated, requiring intubation and vasopressor support. Computed tomography angiogram ruled out pulmonary embolism but revealed extensive pulmonary edema. Bedside echocardiography showed severely reduced left ventricular ejection fraction (∼10-15%) with no pericardial effusion. Cardiac catheterization was considered, but the patient deteriorated rapidly and progressed to cardiogenic shock. Despite advanced resuscitative efforts, including pacing and vasopressor escalation, she expired. Given the timing and absence of other causes, mesalamine-induced myocarditis was deemed the most likely etiology. This section was summarized to fit desired length for abstract submission. Discussion: Mesalamine-induced myocarditis is an extremely rare but recognized complication, typically occurring within the first few weeks of therapy. This case highlights the importance of maintaining vigilance when patients present with new systemic or cardiopulmonary symptoms shortly after starting mesalamine. Prompt recognition and discontinuation may be lifesaving, underscoring the need for clinician awareness of this uncommon yet severe adverse effect.