"Spastic dystonia" or "Inability to voluntary silence EMG activity"? Time for clarifying the nomenclature

We thank Lumsden and colleagues for their comments on ourpaper ‘‘Spastic dystonia in stroke subjects: prevalence and featuresof the neglected phenomenon of the upper motor neuron syn-drome” (Trompetto et al., 2019). We agree with them that preciseterminology is essential for unambiguous communication andsharing of knowledge. Since this goal is far from being achievedin the field of the positive phenomena of the upper motor neuronsyndrome (UMNS), we agree that the time has come to find anomenclature able to capture the essential and unique featuresof the phenomenon so far reported as ‘‘spastic dystonia”, therebyeliminating eventual confusion. Realistically, this should be matterof dedicated reflections, but we welcome the opportunity offeredby Lumsden and colleagues (Lumsden et al., 2019).The main points of the subject (and debate) are the following.First, the currently used term ‘‘spastic dystonia” refers to theinability of patients with UMNS to voluntary silence muscle activ-ity on command (Gracies, 2005; Sheean and McGuire, 2009;Trompetto et al., 2014). This inability leads to spontaneous tonicmuscle contractions, which prove stretch-sensitive (Gracies,2005), and ultimately amplify the velocity-dependent hypertonia(Marinelli et al., 2017; Trompetto et al., 2019Trompetto et al., 2019).Second, as an inability to relax muscles at will, the phenomenonfalls in the most recent definition of dystonia, ‘‘a movement disor-der characterized by sustained or intermittent muscles contrac-tions causing abnormal, often repetitive, movements, postures, orboth” (Albanese et al., 2013).Third, since ‘‘spastic dystonia” may occur in the absence ofvelocity-dependent hypertonia (Denny-Brown, 1966), which isthe hallmark of spasticity, why qualifying this phenomenon as‘‘spastic”? But: if this is not ‘‘spastic”, should it be simply ‘‘dysto-nia”, ‘‘secondary dystonia”, or ‘‘dystonia in the context of theUMNS”?As delineated above, the debate prompts comments that movefrom the phenomenological to the pathophysiological level. Weshortly review strengths and weaknesses for each point, and post-pone eventual solution to more thorough review.From a phenomenological point of view, we consider as undis-puted that dystonia and ‘‘spastic dystonia” manifest similarly,therefore the involuntary muscle activity we are dealing with isdystonic in nature. But it is only one nature of the abnormal move-ment, the second one being its exquisite sensitivity to musclelengthening.Equally undisputed is the clearly distinct pathophysiologybetween ‘‘dystonia” and ‘‘spastic dystonia”. The overwhelmingmajority of papers using the term ‘‘dystonia” refers to clinical con-ditions stemming from structural or functional diseases of thebasal ganglia, unrelated to the activity of the stretch reflex. Onthe contrary, ‘‘spastic dystonia” is found in patients having lesionsoutside the basal ganglia, exhibiting clear abnormality in theexcitability of the stretch reflex circuitry. Because definitely dis-tinct pathological mechanisms give rise to muscle overactivitysharing similar phenomenology, the term ‘‘dystonia” seems inade-quate for describing the involuntary muscle contraction we aredealing with.Even from a nosological perspective, the term ‘‘dystonia”appears inappropriate. By definition, ‘‘dystonia” is amovement dis-order, whereas ‘‘spastic dystonia” is not. Indeed, amovement disor-der(meaning to indicate a disease of the basal ganglia) is definedas a ‘‘neurological syndrome in which there is either an excess ofmovement or a paucity of voluntary and automatic movements,unrelated to weakness or spasticity” (Fahn et al., 2011). It is apod-ictic how much ‘‘spastic dystonia” can be related to both weaknessand spasticity. Corollary is that spastic dystonia can neither beconsideredtout-court‘‘a subset of dystonia” (Lorentzen et al.,2018).For old-fashioned ‘‘motorist” neurologists, the term ‘‘spasticdystonia” reflects perfectly the double nature of the stretch-sensi-tive (although not stretch-induced), spontaneous, tonic musclecontraction that can be observed in the absence of movement (assole inability to relax) or during movement (as associated posturalreactions) in patients affected by UMNS. None of the semanticnuances, such as ‘‘dystonic spasticity” (Lorentzen et al., 2018), or‘‘dystonia with spasticity” or ‘‘dystonia accompanying the UpperMotor Neuron Complex” (as suggested by these respected authors)is likely to improve the understanding or the clarity of this simi-larly old-fashioned concept. But as time goes on, the audience ofphysicians dealing with UMNS patients grows, and we see the needfor changing the term ‘‘spastic dystonia”. Nevertheless, we mustacknowledge the difficulty to find an equally efficacious two-worddescriptor, probably reflecting the peculiarity and complexity ofthis motor phenomenon (sensitivity to - but not dependency fromperipheral input; occurrence both in the absence and during move-ment; ability to cause or not abnormal postures).The letter by Lumdsen et al. (2019) proves that ‘‘spastic dysto-nia” seems no more conducive to the recognition of the phe-nomenon that it wants to identify, probably explaining why it is‘‘the neglected phenomenon of the UMNS” (Trompetto et al.,2019). A newly proposed definition as a ‘‘stretch- and effort-unre-lated sustained involuntary muscle activity following centralmotor lesions” (Lorentzen et al., 2018) certainly avoids confusionin terms of dystonia, but it fails to convey the inability to relaxmuscles, it overestimates the ‘‘un-relation” to muscle stretch, anduncouples this involuntary muscle activity from velocity-depen-dent hypertonia, which is the more evident clinical sign in thesepatients (Marinelli et al., 2017; Trompetto et al., 2019). Aside from shading dystonia vs. spasticity andvice versa,weconsider that ‘‘inability to voluntary silence EMG activity”describes well both the phenomenological and pathophysiologicallevel, the positive phenomenon of the UMNS currently referred toas ‘‘spastic dystonia”. The ensuing stretch-sensitive spontaneoustonic muscle contractions favor/promote velocity-dependenthypertonia, and may produce abnormal postures. This physiologi-cal construct would bring the concept to the clinicians that two arethe causes of velocity-dependent hypertonia: spasticity (Lance,1980) and ‘‘inability to voluntary silence EMG activity”. Such a dis-tinction would help prevent the overdiagnosis of ‘‘spasticity”whenever the clinical examination reveals the presence of veloc-ity-dependent hypertonia, and will strengthen the idea that onlythe use of surface-EMG can discriminate between muscles thatare relaxed prior to passive stretch (i.e., muscles affected by spas-ticity), and those showing stretch-sensitive spontaneous tonic con-tractions (i.e., muscles affected by ‘‘inability to voluntary silenceEMG activity”).