Background: Immune checkpoint inhibitor (ICI)-related myocarditis is a rare but potentially fatal adverse event that can occur following ICI exposure. Early diagnosis and treatment are key to improve patient outcomes. Somatostatin receptor-based positron emission tomography-CT (PET/CT) showed promising results for the assessment of myocardial inflammation, yet information regarding its value for the diagnosis of ICI-related myocarditis, especially at the early stage, is limited. Thus, we investigated the value of ⁶⁸ Ga-DOTA(0)-Phe(1)-Tyr(3)-octreotide (⁶⁸ Ga-DOTATOC) PET/CT for the early detection and diagnosis of ICI-related myocarditis.

Methods: Consecutive patients with clinically suspected ICI-related myocarditis from July 2018 to February 2021 were retrospectively evaluated in this single-center study. All patients underwent imaging for the detection of ICI-related myocarditis using either cardiac magnetic resonance (CMR) imaging or ⁶⁸ Ga-DOTATOC PET/CT. PET/CT images were acquired 90 min after the injection of 2 MBq/kg ⁶⁸ Ga-DOTATOC with pathological myocardial uptake in the left ventricle (LV) suggestive of myocarditis defined using a myocardium-to-background ratio of peak standard uptake value to mean intracavitary LV standard uptake (MBR_peak ) value above 1.6. Patients had a full cardiological work-up including ECG, echocardiography, serum cardiac troponin I (cTnI), cardiac troponin T and creatine kinase (CK), CK-MB. Endomyocardial biopsy and inflammatory cytokine markers were also analyzed. The detection rate of ICI-related myocarditis using ⁶⁸ Ga-DOTATOC PET/CT and CMR was assessed.

Conclusion: The use of ⁶⁸ Ga-DOTATOC PET/CT along with immune correlates is a highly sensitive method to detect ICI-related myocarditis especially in the early stage of myocardial inflammation, as patients with elevated cTnI may present normal CMR imaging results. ⁶⁸ Ga-DOTATOC PET/CT is also useful for detecting concomitant myositis. These results need to be confirmed in a larger population of patients and validated against a histological gold standard if available.