Transcranial magnetic stimulation to predict balance and gait patterns following supratentorial stroke
09 / 2006 - onbekend
Standing and walking disabilities are a major problem in the rehabilitation of patients with stroke. The most characteristic hemiparetic gait patterns at the ankle foot level are insufficient foot clearance during swing, incorrect placement of the hind foot in early stance, disturbed roll-off in mid-stance, and impaired push-off in late stance. Abnormal balance and gait patterns may be the consequence of stroke-related primary impairments as well as of secondary (sometimes compensatory) mechanisms. The primary impairments include altered corticospinal drive to motoneurons, disinhibition of spinal reflexes, and disrupted sensory feedback. Prolonged muscle (co-)activations, muscle stiffness and contractures are well known secondary features. It is far from clear how these primary and secondary mechanisms interact and determine the specific hemiparetic gait abnormalities at the ankle foot level and resulting gait patterns in stroke. The basic question of this research project is to what extent the functional behavior of critical paretic lower leg muscles during standing and walking can be understood and predicted by (early) assessment of the integrity of the corticospinal connections to these muscles using transcranial magnetic stimulation (TMS) in patients with stroke. Standing and walking require highly integrated sensorimotor and higher perceptual functions of the nervous system. A supratentorial stroke may impair these functions, causing more or less severe postural imbalance and walking disability (1-5). Inappropriate timing of muscle activity during the gait cycle, insufficient force control, and the presence of co-activation patterns are characteristic impairments (4). The most characteristic hemiparetic gait abnormalities at the ankle foot level are insufficient foot clearance during swing, incorrect placement of the hind foot in early stance, disturbed roll-off in mid-stance, and impaired push-off in late stance. Recent longitudinal research concerning ambulation after stroke demonstrates that the early-developed hemiparetic movement patterns do not significantly change over time(2,3,5). These results suggest that it should be possible to make early predictions of hemiparetic balance and gait patterns based on more detailed measures of stroke-related primary impairments. Among the primary impairments are altered corticospinal drive to motoneurons, supraspinal disinhibition of spinal reflexes, and disrupted sensory feedback. In addition, prolonged muscle activations both at the nonparetic and at the paretic side may emerge as compensation strategies (4). In the long term, stiffness and contractures may further impair spastic muscle function. It is, however, far from clear how these primary and secondary impairments interact and determine the specific movement patterns. The basic question of this project is to what extent the (long term) functional behavior of critical paretic lower leg muscles during standing and walking can be understood and predicted by (early) assessment of the integrity of the corticospinal connections to these muscles in patients with supratentorial stroke. It is hypothesized that both the force control and timing abnormalities of the lower leg muscles, whether or not mediated by disinhibition of reflexes, are directly related to the integrity of the corticospinal connections to these muscles as assessed by TMS. From this perspective the following research questions will be addressed: The annual incidence of stroke in the Netherlands is about 30.000 new patients each year. Although many of these patients have a potential for functional recovery, a substantial proportion may experience more or less severe long-term balance and walking disabilities as a consequence. In many cases, impairments of lower leg muscles play a critical role in the functional limitations, causing inadequate balance reactions and abnormal foot placement and roll-off during gait. Early prediction of the long-term individual balance and gait patterns would make it possible to better focus rehabilitation strategies towards intensive physiotherapy or, in the case of expected poor recovery, measures to support ankle-foot functions such as individually tailored orthoses or footwear, or various ways of (non)invasive neuromodulation (e.g. peroneal nerve stimulation). Early interventions to prevent secondary consequences of long-term spasticity, such as muscle stiffness and contractures, may be better targeted as well (e.g. early application of neuronal or neuromuscular blockades). Besides early intervention based on clinical prediction, the acquired knowledge of the role of different lower leg muscles in the control of balance and gait after stroke may be used to further improve therapeutic strategies, for instance soft-tissue surgical interventions such as muscle-tendon transfers. I. Transcranial magnetic stimulation of lower leg muscles. The first step in the proposed research project is to optimize and standardize the method of TMS of the lower leg muscles by using a figure-of-eight coil together with modern navigation techniques. This part of the study will be conducted in a sample of 10 patients with chronic supratentorial stroke involving the leg and 10 healthy age-referenced (elderly) subjects. A figure-of-eight coil will be used to allow for more precise spatial cortical stimulation, also of the deeper cortical structures (location of primary motor cortex of the leg muscles along the medial aspects of both cerebral hemispheres). Moreover, a recently developed frame for fixing the subject s head and the stimulator coil will be used and tested to minimize intersubject stimulation variability. This part of the study will lead to a standardized and reliable procedure for using TMS of (lower) leg muscles in patients with supratentorial stroke. Additionally, five of the chronic stroke patients will undergo the gait and balance protocol as delineated below, in order to test the protocol for study II.