Cerebral vasodilation and lesion patterns in stroke-like episodes of MELAS: a quantitative angiographic investigation

Background: The pathophysiology of stroke-like episodes in mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome remains incompletely understood, despite the syndrome's distinctive clinical and radiological characteristics. This study aimed to gain insight into the underlying mechanisms of stroke-like episodes by analyzing vascular and perfusion changes during acute stroke-like episodes. Methods: We conducted a retrospective observational study of genetically confirmed MELAS patients who experienced stroke-like episodes between January 2010 and December 2023. All patients underwent magnetic resonance imaging (MRI) and angiography during the acute phase. Vessel diameters were quantitatively measured at predefined anatomical locations on both the affected and contralateral sides, and were compared using the Wilcoxon signed-rank test. Follow-up imaging was reviewed when available to assess the reversibility of vascular changes. Results: Among the 17 patients, 15 (88.2%) exhibited lesions characterized by cortical cytotoxic edema and subcortical vasogenic edema. Angiographic analysis revealed significant vasodilation of major vessels in 10 patients (58.8%), primarily affecting the middle cerebral artery (MCA) on the symptomatic side. Hyperperfusion was observed in all patients who underwent perfusion-weighted MRI, which spatially corresponded to stroke-like lesions. Quantitative analysis indicated a significant difference in vessel diameter between the affected [1.92 (interquartile range, 1.76-2.42)] and unaffected sides [1.84 (interquartile range, 1.74-2.22), Z=-2.250, P=0.024]. Follow-up angiography was conducted for three patients, all of whom demonstrated complete resolution of vasodilation. Conclusions: Our findings of cortical cytotoxic edema, subcortical vasogenic edema, and reversible major vessel vasodilation during stroke-like episodes contribute to the pathophysiological understanding of MELAS based on mitochondrial energy failure.