Spastic Paresis: A Treatable Movement Disorder

Abstract

If a movement disorder is a neurological condition that causes “excess movement or a paucity of voluntary and involuntary movements,” we propose that spastic paresis represents an archetypical movement disorder and should be considered within this sphere.1 This relates not only to the sign of spasticity, which is defined as the enhancement of velocity-dependent stretch reflexes, measured at rest.2, 3 Spasticity is but the symptomatic hallmark of the syndrome of spastic paresis following lesions that involve pyramidal pathways. Spastic paresis comprises hypokinetic and hyperkinetic movement abnormalities from both muscular and neural causes, which constitute the spastic movement disorder (SMD).1 When considering brain lesions causing syndromes of spastic paresis (eg, stroke, trauma, tumors, inflammatory, or infectious brain disorders), the vast majority are not confined to the pathways of motor command execution, that is the pyramidal pathways. In most cases, neural damage extends to striatal-cortical areas involved in the preparation of motor command, which are extrapyramidal pathways. In some instances, causal lesions even include pathways involved in the conception or the motivation of motor command, causing superimposed symptoms of apraxia or abulia. Even when considering strictly spinal cord injuries, we suggest that the syndromes resulting from those lesions also represent true movement disorders, with hypokinetic and hyperkinetic components. Disruption of motor command execution causes paresis, that is, reduced voluntary motor unit recruitment.4 The resulting signs include insufficient movement acceleration or force.4 A paucity of movement ensues with low amplitude and speed. Paresis of the agonist is the only operative mechanism in the hyperacute stages of paresis. In subacute and chronic stages, agonist paresis becomes combined with increased antagonistic resistances, with muscle and then additional neural impairments, which also contribute to the hypokinetic movement disorder. The individualization of a muscle disorder because of immobilization in unstretched position in the context of paresis is relatively recent. Following stroke, lesion load in the brain and reduced active movement at 48 hours predict later hyper-resistance to stretch from some muscles, with risks of limb deformities and pressure sores.5-8 In his volume Internal Affections, Hippocrates emphasized the need to frequently mobilize the bed-ridden patient—regardless of brain lesion—and the poor prognosis of movement loss from insufficient mobilization.9 In the late 18th century, the anatomist Vicq d'Azyr reported fatty transformation inside immobilized muscles, the outside aspect of the muscle being unchanged.10 The concept of a condition later called disuse atrophy was born, with early measures showing reduction of muscle mass, but no report at the time on muscle extensibility changes.11 It was not immediately understood that disuse in the stretched position was partly protective for the muscle.11 Muscle extensibility may be defined as the amount of muscle lengthening obtained for a given stretching force.1, 4 The first animal studies specifically monitoring muscle extensibility after muscle immobilization in unstretched position were performed in the 1970s.12, 13 Within days of immobilization in unstretched position, muscle extensibility decreases in parallel with sarcomere loss.12-15 From a pathogenetic point of view, these muscle changes are initiated by profound modifications in gene transcription, with falling protein synthesis within 2 hours of the unstretched immobilization onset.16, 17 In parallel, centro-nucleation occurs within the diseased muscle fiber.18, 19 Surrounding collagen bundles stiffen, forming a modified muscle extracellular matrix (ECM) with thickened perimysial cables, enhanced collagen cross-links in endomysium, causing major losses of extensibility.15, 18-20 Of note, associated neurotomy or radicotomy partially protect the uns