Objectives: This study aimed to assess the accuracy and feasibility of cardiac magnetic resonance (CMR) as well as the performance of the updated Lake Louise Criteria (LLC) for myocardial inflammation in cancer patients with acute immune checkpoint inhibitor -associated myocarditis (ICI-M).

Background: ICI are antibodies blocking tumour-driven inhibition of T-cell activation and are currently used for multiple cancer entities. ICI-M represents a rare but severe toxicity of these therapies. Thus, an early and accurate detection is needed. CMR has proven to be a valuable diagnostic tool for the non-invasive detection of myocarditis. The updated LLC of 2018 propose the combination of myocardial edema (T2 map, T2-weighted CMR images) and markers of inflammatory myocardial injury (T1 map, extracellular volume, late gadolinium enhancement (LGE)) as surrogate of strong evidence for myocardial inflammation, but have not yet been validated in ICI-induced myocarditis patients.

Methods: We prospectively enrolled patients with ICI-induced myocarditis to undergo a CMR scan including CINE images, T1/T2 mapping, T2-weighted images and LGE sequences. Additionally, the global longitudinal strain (GLS) was calculated using feature tracking.

Results: From 2019 to 2021, 49 patients were diagnosed with ICI-M at our site. In 33 of these patients, a CMR scan was performed 72h after suspected diagnosis of ICI-M. Diagnostic quality was excellent in 23 patients, good in 10 patients and poor/non-diagnostic in zero patients. In 16 patients (48.5%), the updated Lake Louise Criteria were fulfilled.  Interestingly, in the 17 patients not fulfilling LLC a pericardial effusion was present in 11 (64.7%) and GLS was found to be abnormal in 16 (94.1%) patients. Overall, the incidence of pericardial effusion and abnormal GLS was 69.7% / 90.1%.

Conclusions: CMR is feasible in cancer patients with ICI-induced myocarditis and can be performed with good to excellent image quality. However, adherence to the LLC yields an underdiagnosis of over 50% in our study group. Here, a focus on pericardial effusion and abnormal GLS might improve diagnostic sensitivity and early detection of myocarditis in cancer patients undergoing ICI therapy.