Spastic dystonia in stroke subjects: prevalence and features of the neglected phenomenon of the upper motor neuron syndrome

Abstract

Objective: Spastic dystonia is one of the positive phenomena of the upper motor neuron syndrome (UMNS). It is characterised by the inability to relax a muscle leading to a spontaneous, although stretch-sensitive, tonic contraction. Although spastic dystonia is a recognized cause of muscle hypertonia, its prevalence among hypertonic muscles of stroke subjects has never been investigated.Differently from spasticity, which is an exaggerated stretch reflex, spastic dystonia is viewed as an efferent phenomenon, due to an abnormal central drive to motoneurons.Methods: In 23 hemiparetic stroke subjects showing increased muscle tone of wrist flexors, surface EMG was used to investigate the presence of spontaneous, stretch-sensitive EMG activity in flexor carpi radialis.Results: Spontaneous, stretch-sensitive EMG activity was found in 17 subjects. In the remaining 6 subjects, no spontaneous EMG activity was found. Conclusions:The majority of stroke subjects is affected by spastic dystonia in their hypertonic wrist flexor muscles. Only a minority of subjects is affected by spasticity.Significance: To stop spastic dystonia from being the neglected aspect of UMNS, it is essential to link its definition to increased muscle tone, as occurred for spasticity. Recognizing the real phenomena underling muscle hypertonia could improve its management. Highlights:· 74% of stroke subjects was affected by spastic dystonia in their hypertonic wrist flexor muscles · Only a minority of stroke subjects was affected by spasticity in their hypertonic wrist flexor muscles · Evaluation of EMG activity during static muscle stretch is pivotal to assess spastic dystonia

Sustained involuntary muscle activity in cerebral palsy and stroke: same symptom, diverse mechanisms

“…The decrease in muscle activity during maintained stretch could imply a primarily inhibitory effect of the stretch in CP. Trompetto et al (2019) observe both an increase in mean EMG levels from passive joint extension and a following decrease during 120-s maintained stretch in a stroke group. A noteworthy difference in Trompetto et al (2019) , however, is a higher velocity of passive joint extension, which likely leads to larger contribution from the spastic phasic stretch reflex, and subsequent larger decrease over time in the maintained position.…”

“…The definition of spasticity, as an ‘enhancement of the velocity-dependent stretch responses' ( Lance, 1980 ; Gracies, 2005 ), which is frequently used in research publications, is therefore contained within this classification but does not cover the full range of symptoms in spastic CP. We believe that the persistent increase in muscle tone described in the SCPE classification of spastic CP is partly due to dystonia, which in relation to the spastic movement disorder could be referred to as spastic dystonia ( Denny-Brown, 1966 ; Sheean and McGuire, 2009 ; Lorentzen et al , 2018 ; Trompetto et al , 2019 ). The condition of spastic dystonia has received little attention in the scientific literature but is described as an inability to relax the muscle, persisting despite a lack of voluntary neural activation ( Gracies, 2005 ; Sheean and McGuire, 2009 ; Lorentzen et al , 2018 ; Trompetto et al , 2019 ).…”

“…We believe that the persistent increase in muscle tone described in the SCPE classification of spastic CP is partly due to dystonia, which in relation to the spastic movement disorder could be referred to as spastic dystonia ( Denny-Brown, 1966 ; Sheean and McGuire, 2009 ; Lorentzen et al , 2018 ; Trompetto et al , 2019 ). The condition of spastic dystonia has received little attention in the scientific literature but is described as an inability to relax the muscle, persisting despite a lack of voluntary neural activation ( Gracies, 2005 ; Sheean and McGuire, 2009 ; Lorentzen et al , 2018 ; Trompetto et al , 2019 ). It has therefore been suggested as an important contributor to body deformities, abnormal joint mobility and increased resistance during externally applied movement of affected joints ( Sheean and McGuire, 2009 ; Lorentzen et al , 2018 ).…”

“…Despite these early observations on tonic muscle contractions ( Pollock and Davis, 1930 ; Denny-Brown, 1966 ), the exact nature and cause of spastic dystonia remain to be explored further. Some authors propose that the severity of spastic dystonia is sensitive to the amount and duration of maintained muscle stretch ( Gracies, 2005 ; Trompetto et al , 2019 ) even though the phenomenon also exists in the absence of stretch or effort.…”

Treatment Response to Botulinum Neurotoxin-A in Children With Cerebral Palsy Categorized by the Type of Stretch Reflex Muscle Activation

“…In particular, lengthdependent stretch reflex activation was most prevalent in the semitendinosus (6). Some hypothesize that this lengthdependency reflects more severely affected muscles (2) or muscles with a more complex movement disorder (10). While several underlying pathophysiological mechanisms of the different types of stretch reflex muscle activation have been proposed (2), it is also relevant to verify whether treatment response differs between the two types of stretch reflex activation.…”