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.

Understanding the exact mechanisms of lesion-induced plasticity underlying the phenomena described above faces the fundamental challenge of connecting two fields: that of animal research—with data most often obtained from small quadrupedal animals—characterized by direct neurophysiological or ultrastructural investigation techniques, but usually rudimentary clinical analysis, and that of human research with opposite characteristics, in which disentanglement between the clinical phenomena of spastic paresis may be relatively advanced today, but where only indirect physiological investigations can be carried out, precluding direct demonstration of causal relationships between basic mechanisms and clinical events.³⁴ In addition, the putative mechanisms mentioned below may be themselves causally related to one another. As a consequence, what follows are mostly hypotheses, which can be appreciated by their smaller or greater likelihood. These hypotheses may be classified into spinal and supraspinal mechanisms.

In the months that follow a higher neural injury, neuronal circuits distal to the injury adapt to sudden disfacilitation and inactivity by mostly increasing intrinsic excitability. The time course of excitability recovery is increasingly protracted from simple to complex nervous systems, from frogs to small rodents to humans.³⁵

Beyond a certain threshold of severity, muscle shortening and stiffening on one side of each joint may “drive” impairments by tonically increasing excitatory spindle afferent activity to the homonymous motoneuron.^{2, 21} Such reverse muscle-central nervous system action might occur through synaptic sensitization at the spinal level by chronically increased intramuscular tension and, therefore, intensified muscle afferent firing.^{21, 73} On the side of the shortened and stiffened muscle, motoneuronal hyperexcitability may in turn enhance activation of that muscle, promoting phenomena such as spastic dystonia, synkinesis (causes of hyperkinesis), and spastic cocontraction (cause of hypokinesis). On the opposite side, chronic mechanisms of reciprocal inhibition from the more stiffened muscle may worsen paresis.⁷⁴

In spastic paresis, all of the phenomena reviewed above—paresis, muscle stiffening, spastic co-contraction, synkinesis, spastic dystonia, and spasms—all coalesce to constitute a composite hypokinetic and hyperkinetic spastic movement disorder, asymmetric around joints, causing cosmetic and functional limitations.⁷⁵ Classical teaching generally suggests that movement disorders are solely associated with dysfunction of non-pyramidal systems. However, we suggest that the concepts reviewed here provide further insight into the extent and complexity of the mixed hypokinetic and hyperkinetic movement disorder of spastic paresis.

In practice, patients at risk (ie, with severe initial paresis) should be identified early and considered for multi-modal programs, involving wearable movement sensors and robotic, physical, medical, or surgical tools including blocking agents such as botulinum toxin, or procedures such as neuro-/radicotomies.^{6-8, 76} Among the physical strategies, alternating movement exercises reduce stretch reflexes and cocontractions in short-term studies.^{48, 77} As reviewed above, other techniques such as prolonged muscle remobilization (ie, long-term stretch programs) may partially reverse spastic myopathy, particularly if commenced early.^{12, 14, 16, 17, 28} Guided self-rehabilitation contracts combining chronic self-stretch and maximal alternating efforts have shown efficacy over the long term in controlled studies.⁷⁸

We hope to have provided convincing arguments to support that spastic paresis is a movement disorder because it fits twice into the definition, being a neurological condition that causes both “excess movement” and “a paucity of voluntary and involuntary movements.” We also briefly appraised the large number of potential therapeutic avenues for these patients. It is notable that study and care of patients with spastic paresis were predominantly conducted by neurologists until the 1960s when the emerging rehabilitation medicine gradually took ownership of the domain. Following the concept of the International Medical Society for Motor Disturbances (ISMD), a parent organization of the Movement Disorders Society (MDS),⁷⁹ the MDS Spasticity Study Group was founded, involving neurorehabilitation specialists, movement disorders neurologists, neurophysiologists, and biomechanical engineers. We join in this collaborative group, animated by the commitment to exploring novel approaches to investigate, diagnose, and treat the spastic movement disorder. There is a logical synergy between these efforts and ongoing MDS teaching activities, on botulinum toxin therapy in particular. We also believe that the “Movement Disorders expertise” may prove precious in conjunction with the physiatry care of patients with this condition, and that it would be both a challenging and rewarding strategy for part of the Movement Disorders community to tackle again the complexity of the syndrome of spastic paresis.

J.M.G. received consulting honoraria by Ipsen, Fastox, Merz, and AbbVie. J.W. received consulting honoraria by AbbVie, Ipsen, Medtronic, and Merz. D.S. received research grant support from Allergan/Abbvie and Merz, and consulting honoraria from Allergan/Abbvie, Merz, and Ipsen. D.D. received honoraria for services provided to Allergan, Ipsen, Merz, Lanzhou Institute of Biological Products, Medy-Tox, Revance, Desitin, Syntaxin, AbbVie, Medtronic, St Jude, Boston Scientific, Almirall, Bayer, Sun, Teva, UCB, and IAB-Interdisciplinary Working Group for Movement Disorders; and is a shareholder of Allergan and holds patents on botulinum toxin and botulinum toxin therapy. K.E.A. received royalties from Springer Publishing, Gul Coast Ultrasound; and honoraria from American Academy of Electrodiagnostic and Neuromuscular Medicine, Catalyst Medical Education, and The Cleveland Clinic Foundation. E.L. has received research grants from the National Medical Research Council, Singapore, the Singapore General Hospital, and the National University of Singapore. He receives royalties from McGraw-Hill and has done consulting work or received academic funds from Allergan, Revance, Novartis, and Ipsen. B.B.S. has received honoraria for lectures from Ipsen, Merz, Desitin, Allergan, AbbVie, UCB Pharma, Medtronic, Nordic Infucare, Berlin-Chemie AG, Orion Pharma, and Bial; received honoraria for participating in Advisory Boards from Ipsen, Medtronic, Allergan, Merz, Almirall Nordic, Innoventa Medica, and AbbVie; and received unconditional grants and funding for Investigator initiated clinical trials from Allergan, AbbVie, Nordic Infucare, Merz, Desitin, Toyota Foundation, and Danish Parkinson Association.

(1) Writing of the First Draft; (2) Review and Critique.

J.M.G., J.W., D.D.: 1, 2.

All other co-authors: 2.