Leukoencephalopathies in mitochondrial disorders: clinical and MRI findings.

The second most frequently affected organ in mitochondrial disorders (MIDs) is the central nervous system (CNS). One of the most frequent CNS abnormalities on imaging is the affection of the white matter (WMLs) for which the term, leukoencephalopathies in mitochondrial disorders (LEM), is proposed. The morphology of LEM on imaging is quite variable even within the same type of MID and the same family. LEM can be a subtle or prominent feature on imaging and may go along with or without clinical neurologic or neuropsychological manifestations. WMLs are most likely due to the underlying metabolic defect of the respiratory chain or concomitant oxidative stress, resulting in neuronal death and replacement of neurons by glial cells. WMLs in MIDs frequently give rise to misinterpretation, particularly if the mitochondrial defect is not evident in organs other than the CNS or if the presence of WMLs does not induce consideration of a MID as a differential. The diagnosis of a LEM requires the diagnosis of an MID, the detection of WMLs on imaging, and the exclusion of all possible differentials. Because the presence of LEM has an impact on the prognosis of an MID, all MID patients should undergo cerebral imaging even in the absence of clinical CNS manifestations.