Spasticity and weakness (spastic paresis) are the primary motor impairments after stroke and impose significant challenges for treatment and patient care. Spasticity emerges and disappears in the course of complete motor recovery. Spasticity and motor recovery are both related to neural plasticity after stroke. However, the relation between the two remains poorly understood among clinicians and researchers. Recovery of strength and motor function is mainly attributed to cortical plastic reorganization in the early recovery phase, while reticulospinal (RS) hyperexcitability as a result of maladaptive plasticity, is the most plausible mechanism for post-stroke spasticity. It is important to differentiate and understand that motor recovery and spasticity have different underlying mechanisms. Facilitation and modulation of neural plasticity through rehabilitative strategies, such as early interventions with repetitive goal-oriented intensive therapy, appropriate non-invasive brain stimulation, and pharmacological agents, are the key to promote motor recovery. Individualized rehabilitation protocols could be developed to utilize or avoid the maladaptive plasticity, such as RS hyperexcitability, in the course of motor recovery. Aggressive and appropriate spasticity management with botulinum toxin therapy is an example of how to create a transient plastic state of the neuromotor system that allows motor re-learning and recovery in chronic stages.
According to the CDC, approximately 800,000 people have a stroke every year in the United States. The continued care of seven million stroke survivors costs the nation approximately $38.6 billion annually. Spasticity and weakness (i.e., spastic paresis) are the primary motor impairments and impose significant challenges for patient care. Weakness is the primary contributor to impairment in chronic stroke (1). Spasticity is present in about 20–40% stroke survivors (2). Spasticity not only has downstream effects on the patient’s quality of life but also lays substantial burdens on the caregivers and society (2).
Clinically, poststroke spasticity is easily recognized as a phenomenon of velocity-dependent increase in tonic stretch reflexes (“muscle tone”) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex (3). Though underlying mechanisms of spasticity remain poorly understood, it is well accepted that there is hyperexcitability of the stretch reflex in spasticity (4–7). Accumulated evidence from animal (8) and human studies (9–18) supports supraspinal origins of stretch reflex hyperexcitability. In particular, reticulospinal (RS) hyperexcitability resulted from loss of balanced inhibitory, and excitatory descending RS projections after stroke is the most plausible mechanism for poststroke spasticity (19). On the other hand, animal studies have strongly supported the possible role of RS pathways in motor recovery (20–36), while recent studies with stroke survivors have demonstrated that RS pathways may not always be beneficial (37, 38). The relation between spasticity and motor recovery and the role of plastic changes after stroke in this relation, particularly RS hyperexcitability, remain poorly understood among clinicians and researchers. Thus, management of spasticity and facilitation of motor recovery remain clinical challenges. This review is organized into the following sessions to understand this relation and its implication in clinical management.
• Poststroke spasticity and motor recovery are mediated by different mechanisms
• Motor recovery are mediated by cortical plastic reorganizations (spontaneous or via intervention)
• Reticulospinal hyperexcitability as a result of maladaptive plastic changes is the most plausible mechanism for spasticity
• Possible roles of RS hyperexcitability in motor recovery
• An example of spasticity reduction for facilitation of motor recovery