Motor control deficits of orofacial muscles in cerebral palsy.

Abstract

SUMMARY Voluntary control of the masseter and orbicularis oris superioris muscles was examined in able bodied and cerebral palsied subjects using visual tracking tasks. A smoothed measure of muscle activity (the full-wave rectified and low-pass filtered electromyogram) was presented as a marker on a computer display screen and the subjects could control the vertical position of the marker by voluntarily altering the level of isometric contraction of one of the muscles. A target marker was also displayed on the screen and the subjects were required to follow or "track" the irregular movements of this target with the response marker. Their success in aligning the response marker with the target was analysed for these orofacial muscles. The masseter is influenced by muscle spindle based reflexes, while the orbicularis oris superioris lacks such reflex control. The cerebral palsied subjects displayed similarly poor control over both muscles, implying that their voluntary motor deficits are not related to abnormal muscle spindle based reflexes. It is suggested that the impairment may be related to perceptual-motor integration.The prevailing theories concerning motor dysfunctions in cerebral palsy generally are dependent upon the disruptive effect of abnormal reflexes on motor control.`4 While the pathophysiology of cerebral palsy involves voluntary deficits as well as the loss of reflex control2 " it is the latter which is used to categorise the motor dysfunction. Recently, it has been suggested that the major deficit may not be abnormal reflex activity imposing restraints on posture and movement, but that all descending motor commands, including reflex control and muscle contraction signals, are inappropriate.5-9 In the absence of reflex effects, motor control is thought to be exceedingly poor and not due solely to damage to the descending pyramidal tract.7-9Evidence supporting the proposition that descending motor commands in cerebral palsy are inappropriate has been based on observing motor control after removal of reflex constraints. For example, the suppression of spinal reflexes by anti-spastic drugs such as baclofen and phenol does not parallel any improvement in motor performance.7 1011 Simi

Reducing Spasticity to Control Muscle Contracture of Children With Cerebral Palsy

“…The range of voluntary joint rotation increased significantly in two children, only one of whom had a significant reduction in spasticity. This may reflect the dissociation between spasticity and voluntary control which has been reported in a number of studies of cerebral palsy (Milner-Brown and Penn 1979, Neilson and McCaughey 1982, Barlow and Abbs 1984, Brown et al 1987, Vaughan et al 1988. Voluntary control may have improved in these two children, independent of the level of spasticity, as a result of 'practice' at maximum joint rotation.…”

Do the unintended actions of botulinum toxin at distant sites have clinical implications?

“…Facial muscles do not act on joints, they have few or no proprioceptors, and their motoneurons neither undergo reciprocal inhibition nor possess the axon collaterals needed to receive recurrent inhibition. [34][35][36][37] Hence, BT injected into facial muscles is unlikely to alter sensory input, and other mechanisms must be evoked to explain BT-induced central effects. Remarkably, altered facial motor output commonly leads to cortical reorganization.…”

Temporomandibular disorders in cerebral palsy: literature review

“…Ries and Berzin (2005) compared children with CP and healthy children, using the modified Ashworth scale for measuring the degree of spasticity in places where a higher incidence of changes in jaw movements was observed, such as lateral deviations and protrusions, in children with CP. Other studies show no correlation between the severity of TMD and the degree of spasticity (VAUGHAN, NEILSON and O'DWYER, 1988;MARIA, 2002). Alfaro, Gonzalez, Robles et al (1999) demonstrated that the masseteric inhibitor reflex obtained in young individuals and adults with CP is not altered by the disease's subgroup (spastic group or athetosis group), but by the patients' type of occlusion.…”

“…According to Maria (2002) and Vaughan, Neilson and O'Dwyer (1988), patients with CP who are more neurologically compromised have higher functional involvement of the masticatory system and structural involvement of the temporomandibular joint (TMJ). This is undoubtedly due to the increase in muscle spasticity, and limitations in jaw movements.…”