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MELAS


KEY FACTS

Terminology

  • M itochondrial myopathy, e ncephalopathy, l actic a cidosis, and s troke-like episodes (MELAS)

  • Inherited disorder of intracellular energy production caused by point mutation in mtDNA

Imaging

  • Stroke-like cortical lesions crossing vascular territories

    • Posterior location most common

  • “Shifting spread” (appearance, disappearance, reappearance elsewhere) is classic

  • Lactate “doublet” at 1.3 ppm in 60-65%

    • Elevated lactate in cerebrospinal fluid, “normal” brain on MRS

  • Basal ganglia lesions and calcifications

Pathology

  • mtDNA contribution to zygote exclusively maternal inheritance

  • Caution: Relationship of phenotype to genotype complex, variable

  • Mutations may present as MELAS but also as other mitochondrial phenotypes

Clinical Issues

  • Classic MELAS triad: Lactic acidosis, seizures, stroke-like episodes

    • Onset of stroke-like episodes usually occurs in childhood/early adulthood

    • Also: Sensorineural hearing loss, diabetes, short stature

  • Heteroplasmy and random mitotic mtDNA segregation, tissue-to-tissue variability → phenotypic heterogeneity and “overlap” with other mitochondrial syndromes

  • Carrier prevalence of m . 3243A > G mutation 0.6% or 60 per 100,000 individuals

Diagnostic Checklist

  • Think

    • MELAS in patient with acute stroke-like cortical lesion that crosses usual vascular territories

  • Consider

    • MELAS in adult presenting with unusual and recurrent stroke-like episodes

Axial graphic shows pathology of MELAS. Acute gyriform cortical swelling that crosses vascular territories is depicted
. Note old lacunes
, generalized/focal atrophy with large sulci
.

Axial FLAIR MR in an 8-year-old girl with short stature and new-onset stroke-like symptoms reveals a focus of abnormally increased signal intensity in the right thalamus
and extensive hyperintensity and abnormal thickening of the cerebral cortex
in the right occipital lobe. The underlying WM is largely spared.

Axial T2WI MR in the same patient shows similar abnormal signal hyperintensity lesions in the same thalamic focus of signal increase
and in the edematous right occipital cortex
. Note the prominent subarachnoid spaces, which may result from malnutrition, medications, or the disease process itself.

Axial DWI MR demonstrates reduced diffusion in the affected regions of the brain
, confirming the acuity of the lesion.

TERMINOLOGY

Abbreviations

  • Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS)

Definitions

  • Inherited disorder of intracellular energy production caused by point mutations in mitochondrial DNA (mtDNA)

IMAGING

General Features

  • Best diagnostic clue

    • Acute: Stroke-like cortical lesions

      • –

        “Shifting spread” (appearance, disappearance, reappearance elsewhere) is classic

      • –

        Lesions cross typical vascular territories

  • Location

    • Stroke-like: Parietooccipital > temporoparietal

    • Calcifications: Basal ganglia (BG)

  • Size

    • Variable, progressive, multifocal

  • Morphology

    • Acute: Gyral swelling

    • Chronic: Supra- and infratentorial atrophy, deep white matter (WM), & BG lacunar infarcts

CT Findings

  • NECT

    • Symmetric BG calcification

  • CECT

    • Variable gyral enhancement

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