Black toenail sign
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The black toenail sign is a radiological sign described in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) on MRI.
The sign describes the subacute appearance of radiological correlates of stroke-like episodes, whereby there are small regions of deep cortical or juxtcortical T2/FLAIR hypointensity, surrounded by hyperintensity 1,2. The hypointensity gives the appearance of a black toenail against the surrounding hyperintense toe 1. It is thought that this hypointensity represents cortical laminar necrosis, which has been histologically proven to occur in MELAS 1.