[Quantitative approach of postural asynergia in cerebellar diseases]

In his original description of cerebellar asynergia, Babinski, in 1899, presented a patient with cerebellar dysfunction performing a backward upper trunk bending. When the patient tried to bend his head and trunk, his lower limbs stayed almost motionless, because the associated flexion of the knee and hip, usually observed in a normal subject, did not take place. To reassess the possibility that asynergia may actually be a symptom of cerebellar dysfunction, a combined kinematic and electromyographic (EMG) analysis of the upper-trunk bending was performed on 3 patients suffering from progressive cerebellar ataxia of late onset and showing a significant atrophy of the vermis on MRI examination. Compared with 3 age and sex-matched control subjects, a significant slowing down of the upper-trunk displacement and a marked reduction of the associated displacement of hip and knee was observed. EMG recordings of three pairs of antagonistic muscles at trunk level (rectus abdominis, erectores spinae), at thigh level (vastus lateralis, semi membranosus), and at leg level (tibialis anterior, gastrocnemius lateralis), showed that the reciprocal activation pattern characteristic of a normal fast movement was absent at the thigh level in the cerebellar patients. This lack of reciprocal activation of the thigh muscles during the upper-trunk bending might explain the reduction of the compensatory displacement of the hip and knee. It might also represent an essential feature of cerebellar dysfunction in provoking axial asynergia between the upper-trunk, which is the moving segment, and the leg, which is the supporting segment during equilibrium control and during whole body displacement.