To the Editor.
—I have noticed that patients with corticospinal tract involvement of the upper limb when asked to extend their arms, palms facing each other, display an upgoing thumb sign as shown in the Figure.
Hachinski V. The Upgoing Thumb Sign. Arch Neurol. 1992;49(4):346. doi:10.1001/archneur.1992.00530280026009
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