Black toenail sign

Last revised by Rohit Sharma on 14 Jan 2023

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.

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