In a recently published article, Elliott et al. (1) determined the prevalence and prognostic significance of unrecognized myocardial infarction (MI) by delayed-enhancement MRI in asymptomatic patients with diabetes without known cardiac disease. Data from the cohort were collected under rigid methodological conditions with very low loss to follow-up and appropriate statistical data analysis. The authors concluded that unnoticeable MI is prevalent in asymptomatic patients with diabetes and confers a markedly increased risk of death and clinical MI, providing significant incremental prognostic value over traditional variables.
These data are welcome given the need for improvements in risk prediction models for patients with diabetes. Interestingly, an explanation of the results obtained by Elliott et al. can be found in an article published 42 years ago. Indeed, MI is the prime cause of death among adult patients with diabetes, and in a nonnegligible number of cases patients do not feel pain or they experience strikingly atypical symptoms. Therefore, diagnosis can be neglected with a consequent increment in mortality rates. In search of an explanation for painless MI in these patients, several decades ago we studied histologic sections of the autonomic nerve fibers of the heart muscle with silver and combined staining techniques, searching for lesions in the sympathetic or parasympathetic nerve fibers that conduct pain (2). In the cases of painless MI studied, nerve fibers showed typical lesions of diabetic neuropathy, namely, beaded thickenings, spindle-shaped thickenings, fragmentation of fibers, and diminished number of nerve fibers. Conversely, patients in the control groups (comprising patients with diabetes with painful MI or without MI and patients without diabetes with painful MI or without MI) presented no evidence of nerve lesions. These findings led us to assume that the absence of pain in patients with diabetes with MI could be due to a lesion of the afferent nerves that conduct pain. Therefore, taking into account that the cardinal sign of acute MI is precordial pain, the clinical findings of Elliott et al. (1) can be clearly explained by structural lesions. As stressed in our article, among patients with diabetes with heart failure or ketoacidosis of unknown origin, painless MI should always be suspected (2). Moreover, the findings of Elliott et al. highlight the potential usefulness of screening with advanced cardiac imaging in asymptomatic patients with diabetes in order to identify a high-risk group that may benefit from aggressive intervention (1). In this regard, it is noteworthy that delayed-enhancement MRI alone, without T1-weighted images with and without fat suppression, can miss areas with lipomatous metaplasia, a relatively common finding in old MI. Therefore, the true prevalence of MI in the cohort of patients included in the study by Elliot et al. could have been higher than that reported (3,4).
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Duality of Interest. No potential conflicts of interest relevant to this article were reported.
