[A lumbosacral cord infarction causing focally accentuated atrophy of the peroneal muscles].

We report focally accentuated atrophy in a muscle due to a cryptogenic lumbosacral infarction. A 56-year-old female rapidly developed left-dominant weakness of lower thigh muscles, sensory loss of all modalities in the L5 and sacral dermatomes, and difficulty in voiding. MRI performed on day 9 showed gadolinium-enhanced lesions in the epiconus. The anterior horn lesion was most prominent in the left side of the epiconus. After one and a half months, the left lower thigh muscles became atrophic especially in the proximal part of the anterior lower thigh. After 4 months, on T2-weighted images, atrophy and high intensities were accentuated in the proximal part of the anterior lower thigh muscles where denervation potentials were abundant. A topographic relationship has been documented between the locus of a motor neuron in the anterior horn column and the position of its motor unit in the muscle. We consider that the distribution of denervation changes on muscle MRI corresponded with the anterior horn lesion on spinal MRI in our case.