Reply: Nonischemic Cardiomyopathy: Just a Diagnosis of What You Don't HaveOpen Access

Introduction

I read with pleasure the letter of Dr Bevan and colleagues, regarding our pilot report about biopsy-proven myocardial inflammation (M-Infl) in genetic cardiomyopathies.¹ The main point they raise is about the discordance between ¹⁸F-fluorodeoxy-glucose positron emission tomography (FDG-PET) scan and biopsy in this setting.

The apparent discrepancy is unlikely to be caused by the biopsy sampling site. As we reported in the Supplemental Appendix,¹ all patients in our pilot report (n = 25) underwent right ventricular biopsy, which is probably less accurate than a voltage map–guided approach to target the disease substrate. Rather, the reason for biopsy positivity was more time- than site-sensitive. At the time of biopsy, most patients in the series had acute, myocarditis-like clinical presentation of cardiomyopathy, known as the “hot-phase.”²

A second relevant point is that the European Society of Cardiology criteria were applied to define myocarditis, based on recognized histological and immunohistochemical criteria.³ The definition of “borderline” myocarditis is accepted when all diagnostic criteria are met except for necrosis, as occurred in 21 of 25 cases.¹ Because most patients had a hot-phase presentation, sampling error may have accounted for the underdetection of necrosis.

A final clarification is needed about the challenging diagnostic role of FDG-PET. I fully agree with Bevan and colleagues on the fact that a hypermetabolic status may be frequently found in genetic cardiomyopathies independently of M-Infl. However, we recently reported the diagnostic role of FDG-PET in arrhythmic myocarditis.⁴ Whereas the significance of FDG-PET abnormalities in genetic cardiomyopathies is still to be demonstrated, all patients with abnormal FDG uptake in the series (8 of 8) had biopsy-proven M-Infl.¹

To conclude, it is a matter of definitions. Similarly, the lack of obstructive coronary artery disease is currently required to define “nonischemic” cardiomyopathies. Nonetheless, patients with nonischemic cardiomyopathies may experience either myocardial infarction or inducible ischemia from coronary microvascular dysfunction. Evidence-based reclassification is called also to differentiate true acute myocarditis from M-Infl associated with hot-phase nonischemic cardiomyopathies, as well as to clarify the significance of any FDG uptake abnormality. Meanwhile, a multimodal diagnostic work-up is reasonably the best way to enable optimal patient-tailored clinical management.²

Footnotes