New Insights for a Better Understanding of the Pusher Behavior: From Clinical to Neuroimaging Features

Abstract

Disorders of postural balance are common in patients with encephalic lesions. According Tyson et al. (Tyson et al., 2006), around 80% of patients experiencing their first cerebrovascular event have static or dynamic postural imbalance. Historically, the first description of postural balance dysfunction in stroke patients dates back to more than one hundred years ago. In 1909, Beevor described the occasional lack of lateral balance in stroke patients that cause them to fall towards their contralesional side due to their paresis (Beevor, 1909). Later, Brunnstrom reported the ‘listing phenomenon’ as a list toward the affected side that patients cope by climbing onto something with their nonparetic hand to prevent listing (Brunnstrom, 1970). In 1968, a tendency to fall towards the lesion side and lateropulsion were described by Bjerver and coworkers in patients with Wallenberg’s syndrome due to dorsolateral medullary infarction (Bjerver S Brandt D Dieterich, 2007). Another postural imbalance observed in patients with encephalic lesions is thalamic astasia. According to Masdeu and Gorelick, this disorder is characterized by the inability to maintain an unsupported upright posture even without paresis or sensory or cerebellar deficits.8 When asked to sit up, patients with this disorder use the unaffected arm to pull themselves up (Masdeu & Gorelick, 1988). This behavior could be explained in part by a vestibular tone imbalance in the roll plane, especially since skew deviation was included as a feature of the syndrome (Brandt & Dieterich, 2000; Dieterich, 2007). As opposed to all other syndromes and phenomena described above, the pusher behavior (PB) is characterized by actively pushing away from the nonparetic side (Davies, 1985). Moreover, patients with PB lean to the side opposite the lesion and strongly resist any attempt at passive correction of their tilted body while sitting or standing. In the most severe cases, this resistance occurs even in a supine position (Pedersen et al., 1996; Lafosse et al., 2005). Such patients report a fear of falling towards their ipsilesional side (Davies, 1985; Pedersen et al., 1996; Lafosse et al., 2005) and are not aware that their active pushing is counterproductive and makes it impossible for them to stand without assistance (D'Aquila