MELAS syndrome (mitochondrial
myopathy, encephalopathy, lactic acidosis, strokes)
Axial-FLAIR and diffusion-weighted images as well as magnetic resonance (MR) spectroscopic
imaging data are provided. The FLAIR image demonstrates bilateral cortical- and
subcortical-signal abnormality within the temporal and parietal lobes with swollen
gyri and compressed sulci. Signal abnormality is much worse on the right. Diffusion-weighted imaging demonstrates restricted diffusion affecting the cortex in the same distribution. MR
spectroscopy spectra sampling the area of FLAIR-signal abnormality demonstrate a
markedly elevated lactate doublet at a TE of 30 ms, which inverts at a longer
TE of 130 ms.
Mitochondrial myopathy, encephalopathy, lactic acidosis,
strokes or MELAS Syndrome represents a group of genetic disorders, which occur
secondary to mutations in mitochondrial DNA. Therefore, there is exclusive
maternal inheritance. The genetic mutation results in abnormal protein
synthesis, which affects the aerobic respiratory chain, ultimately resulting in
a decrease in NADH+ and NAD+. Because there is malfunctioning aerobic metabolism, the body shifts to anaerobic metabolism, which results in a buildup of neurotoxic lactic acid.
Patients with MELAS present at an average age of 15 years
with 90% of patients presenting before the age of 40. Common signs and symptoms
include seizures, stroke-like episodes, muscle weakness, sensineural hearing
loss, exercise intolerance, headaches, nausea/vomiting, short stature, and
cognitive deficits. The course of MELAS is progressive with acute exacerbations.
Computed tomography (CT) is not particularly useful for
MELAS and may only show symmetric basal ganglia calcifications. MR imaging
features of acute MELAS include swollen gyri and compressed sulci with T2/FLAIR
hyperintensity within the cortex and subcortical white matter, most commonly
parietooccipital and temporoparietal. Diffusion-weighted imaging demonstrates
restricted diffusion in the same distribution.
Classically there is “shifting spread” of the affected regions during
acute episodes with appearance, disappearance, and reappearance elsewhere. Contrast-enhanced
images may show gyral enhancement during acute episodes. Chronic MELAS will
show cortical atrophy involving the affected portions of the temporal,
parietal, and occipital lobes as well as basal ganglia atrophy and hyperintensity.
Spectral imaging usually, but not always, demonstrates an
elevated lactate doublet at 1.3 ppm. Confirmation that the peak represents
lactate can be accomplished by using a long TE (approximately 135 ms), which will
invert the doublet. A short TE of 30 ms will show an upright lactate
Elevated lactate levels are often found in CSF as well as blood. Often muscle biopsy is used to
confirm the diagnosis of MELAS by identifying ragged red fibers as well as
specific mitochondrial enzymes.
- Castillo M, Kwock L, Green C. MELAS Syndrome: Imaging and proton MR spectroscopic findings. AJNR Am J Neuroradiol. 1995;16:233–239.
- Kim IO, JH Kim, WS Kim et al. Mitochondrial myopathy-encephalopathy-lactic acidosis-and
stroke-like episodes (MELAS) syndrome: CT and MR findings in seven children. Am. J. Roentgenol. 1996;166: 641-645.