We noticed that in patients with pyramidal lesion, the distance between the finger and nose on repeated finger-nose testing shortens progressively in the paretic hand. The shortening of distance is also present in those patients in whom, on routine neurological examination, no obvious weakness, pronation drift, or changes in tone and reflexes can be found.
The patients set u the starting point of the finger at a progressively shorter distance from the nose, despite the efforts of the examiner to correct the shortening. This shortening or lazy arm phenomenon can be explained by primary affection of the extensor muscles in upper limbs by a corticospinal lesion, resulting in the tendency to flexion and pronation of the elbow.1-4 The increased tone of the elbow flexors and pronators acts as an agonist during finger-nose touching, and as an antagonist on rendering of the finger to its primary position, thus causing a
Pollak L, Klein C, Rabey J. The Distance Shortening Phenomenon or the Lazy Arm Sign as a Subtle Pyramidal Sign. Arch Neurol. 1997;54(8):935. doi:10.1001/archneur.1997.00550200005001