Epidemiology and characteristics of occipital brain infarcts in young adults in southwestern Finland.

Occipital stroke and occipital epilepsy are possible manifestations of mitochondrial diseases. A previous study in northern Finland suggested a frequency of 10% for mitochondrial disorder in young patients with stroke. Here we studied the epidemiology of occipital brain infarcts in a defined population in southwestern Finland. Patients diagnosed with brain infarct or visual field defect with onset at the ages of 18-45 years were identified from the discharge files at the Turku University Hospital. We further ascertained those patients with an occipital brain infarct in brain imaging or homonymous hemianopia with no signs of other etiology in brain imaging. We reviewed the clinical data for known stroke risk factors and analyzed samples for the m.3243A > G and m.8344A > G mutations in mitochondrial DNA (mtDNA), and determined mtDNA haplogroups and five common mutations in the gene encoding polymerase gamma (POLG1). Migraine was more common in young patients with occipital brain infarct than in the general population, especially among women. None of the patients harboured the m.3243A > G or m.8344A > G mutation in mtDNA or any of the five common mutations in POLG1. Interestingly, 17% of the men and 33% of the women belonged to the mtDNA haplogroup Uk, while its frequency in the general population is 17%. Our results suggest that mtDNA haplogroup Uk is associated with increased risk of occipital stroke in young women. POLG1 mutations have been associated with occipital epilepsy, but we did not find the common mutations in patients with occipital stroke.

Evolution of brain imaging abnormalities in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes.

An 18-year-old man developed consecutive homonymous hemianopias that were eventually attributed to mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS). The diagnosis was initially suspected when brain CT scans showed bilateral dystrophic basal ganglia calcifications and MR spectroscopy later showed a prominent lactate peak. Diffusion-weighted MRI showed progressive evolution of restricted proton diffusion at the margins of the lesion from day 3 through 3 weeks. Genetic testing from peripheral blood confirmed an A3243G transition in the patient's MTTL1 gene encoding the transfer RNA for leucine. The patient's visual function improved, but severe atrophy of gray and white matter was visible on MRI.