P0401 - Myocarditis Masquerade: A Rare Cardiac Presentation of Acute Myeloid Leukemia

Introduction:
Acute myocarditis is a potentially life-threatening illness characterized by myocardial inflammation. While viruses are commonly implicated, etiologies are numerous. We present a previously healthy teenager diagnosed clinically with acute myocarditis ultimately found to have acute myeloid leukemia (AML).

Case Description:
A previously healthy 13 yo male presented with 1 day of chest pain and dyspnea and 4 days of headache, neck pain, malaise, and anorexia. On presentation, he was afebrile, persistently tachycardic (up to 133 bpm) with normal blood pressure and perfusion. Labs (Table 1) were notable for elevated troponin-I, CRP, LDH, uric acid and haptoglobin with leukocytosis and thrombocytopenia. EKG demonstrated ST elevation in lateral leads (Figure 1). CXR was unremarkable. Echocardiogram revealed normal LV size and low-normal systolic function (EF 53%) with mild inferior and posterior septal wall hypokinesis and no pericardial effusion. CT chest at referring hospital noted mild right perihilar enlargement.
Given risk for acute decompensation, he was admitted to cardiology for management of acute myocarditis. Oncology was consulted and recommended IVF/allopurinol for tumor lysis syndrome. Within hours of IVF initiation, troponin substantially decreased to 8.45 ng/mL. Review of peripheral smear revealed an abnormal cell population resembling myelomonoytic blasts with auer rods. AML was confirmed 12 hours later via peripheral flow cytometry. Induction chemotherapy (Cytarabine, Daunorubicin, Etoposide, and, later, Gemtuzumab Ozogamicin) began within 24 hours. Troponin continued to decrease (0.099 ng/mL on day 4), and EKG normalized with initial chemotherapy. Repeat echocardiogram 2 days later showed improved LV systolic function (EF 62%) without segmental wall motion abnormalities. Cardiac MRI is pending at this time.

Discussion:
Myocarditis is a rare presentation of AML in pediatric patients and likely results from leukemic infiltration of the myocardium. Although previously described, this is largely limited to autopsy studies from the 1960s, which found leukemic infiltration in nearly 50% of leukemia patients. In the current era, where 5-year survival for all subtypes of leukemia exceeds 60%, understanding the clinical presentation is critically important. Prior reports identified type of leukemia and peripheral lymphocyte count as risk factors for infiltration, often multifocal and associated with LV hypertrophy. Cardiac MRI with gadolinium may reveal active myocardial inflammation and edema in sites of infiltrate confirmed by endomyocardial biopsy, although biopsy is invasive and may delay treatment. Failure to recognize an underlying oncologic etiology of myocarditis can result in delayed diagnosis and significant morbidity and mortality. While systolic function ultimately normalized allowing for standard dose anthracycline chemotherapy, his abnormal echocardiogram and troponin at presentation will require close cardiology follow-up with this potentially cardiotoxic therapy.

Conclusion:
This case highlights the importance of including a broad differential for myocarditis as well as multispecialty teamwork to initiate lifesaving treatments in the setting of competing pathophysiologies.