Department of Neurosurgery, Monash Health, Melbourne, Australia.
Department of Surgery, Monash University, Melbourne, Australia.
Clin Anat. 2021 Apr;34(3):478-482. doi: 10.1002/ca.23715. Epub 2020 Dec 31.
Pyramidal weakness, that is, the weakness that preferentially spares the antigravity muscles, is considered an integral part of the upper motor neuron syndrome. Despite its name, pyramidal weakness has very little to do with the pyramidal tract, and preeminent texts on neurology, neuroanatomy, and clinical examination differ considerably in their descriptions and localization of this enigmatic finding. Evidence from human and nonhuman primate studies demonstrates that lesions confined only to the corticospinal (pyramidal) tract cause significant deficits in fine motor control of the hand, but do not cause posturing or patterned weakness of the extremities. Lesioning of the corticofugal fibers, particularly the corticoreticular and corticopontine tracts, leads to dysbalanced output from reticulospinal, and vestibulospinal systems, which along with changes in rubrospinal tract output balance, probably accounts for the pyramidal weakness pattern. Importantly, this would delineate that pyramidal weakness could only be incited by lesions above the brainstem. It has also been suggested that the inherently greater strength of the antigravity musculature is the substrate for pyramidal weakness, independent of any preferential motor innervation. These hypotheses require further testing in myometric studies with carefully selected participants.
锥体束无力，即优先保留抗重力肌肉的无力，被认为是上运动神经元综合征的一个组成部分。尽管它的名字是这样，但锥体束无力与锥体束几乎没有关系，而且在神经学、神经解剖学和临床检查的主要著作中，对这一神秘发现的描述和定位差异很大。来自人类和非人类灵长类动物研究的证据表明，仅局限于皮质脊髓（锥体束）的损伤会导致手部精细运动控制的显著缺陷，但不会导致姿势或四肢模式性无力。皮质传出纤维（特别是皮质网状和皮质脑桥纤维束）的损伤会导致网状脊髓、前庭脊髓系统的不平衡输出，加上红核脊髓束输出平衡的改变，可能是导致锥体束无力模式的原因。重要的是，这将表明锥体束无力只能由脑干以上的损伤引起。也有人认为，抗重力肌肉固有的更大力量是锥体束无力的基础，与任何优先的运动神经支配无关。这些假说需要在对精心挑选的参与者进行肌电图研究中进一步验证。
