Key points

Introduction

Movement disorders constitutes a subspecialty of neurology focusing on a variety of conditions characterized by hypokinetic, hyperkinetic, or abnormally coordinated movements, which include tremor, dystonia, parkinsonism, myoclonus, chorea, ballismus, tics, restless limbs, and ataxia, among others. The term “movement disorders” may be used to refer to either abnormal movements or syndromes that cause such abnormal movements. The classification of movement disorders is based on phenomenology, individual syndromes, or etiology. This article reviews the terminology used to describe movement disorders, discusses individual movement disorders and their occurrence in patients with multiple sclerosis (MS), and reviews treatment options.

Introduction

Movement disorders constitutes a subspecialty of neurology focusing on a variety of conditions characterized by hypokinetic, hyperkinetic, or abnormally coordinated movements, which include tremor, dystonia, parkinsonism, myoclonus, chorea, ballismus, tics, restless limbs, and ataxia, among others. The term “movement disorders” may be used to refer to either abnormal movements or syndromes that cause such abnormal movements. The classification of movement disorders is based on phenomenology, individual syndromes, or etiology. This article reviews the terminology used to describe movement disorders, discusses individual movement disorders and their occurrence in patients with multiple sclerosis (MS), and reviews treatment options.

Tremor

Tremor is an involuntary rhythmic oscillation of a body part caused by alternate or synchronous contraction of agonist and antagonist muscles. Rest tremor is the term given to tremors that occur when the body part is completely at rest. Action tremors can be of 3 different types: they can occur in posture when the limb is held against gravity; they can occur during movement, as in kinetic tremors; and they can present at the end of a target-guided movement, as in intention tremors.

Tremor is a common problem in MS and was in fact noted in the original triad of symptoms attributed to MS by the French neurologist Charcot, the other 2 symptoms being scanning speech and nystagmus. Tremor can be seen in anywhere between 25% to 58% of patients with MS, and has been associated with significant impairment of function and disability. Tremor is also often seen in secondary progressive MS. Estimates of the incidence of severe tremor in MS have ranged from 3% to 15%, and patients with MS tremor of any severity are more likely to be unemployed or retired early owing to disability. Tremor in MS is most often a combination of postural and intention tremor, with the distal limb being more often involved than the proximal structures. MS tremor can be bilateral and most often affects the upper limbs, although it may also involve the head, neck, or vocal cords.

The pathophysiology of tremor in MS is not clear, as it rarely occurs in isolation and is usually associated with other neurologic signs and symptoms. MS tremor is thought to be mediated through the cerebellum and its connections, because of the postural and intention nature of the tremor. Rest tremors are uncommon in MS. Cooling of the limbs has been shown to reduce the intensity of the MS tremor, and this is thought to be a surrogate marker of the role of the cerebellum in MS tremor. Cooling reduces muscle-spindle excitability and slows down nerve conduction, and hence likely reduces input into the tremor-producing cerebellar circuitry. The fact that upper limb tremor severity correlates highly with the degree of ataxia, dysdiadochokinesia, and dysmetria also supports the role of the cerebellar connections in the pathogenesis of MS tremor. One study showed that the tremor amplitude correlated with the MS lesion load in the contralateral pons and that bilateral tremors were associated with higher lesion load in the bilateral pons, suggesting involvement of the cerebellar input and outflow pathways.

Treatment of tremors in MS is challenging, which is partly due to poor response to medications but also to the associated neurologic symptoms that compound the disability. It is also difficult to segregate MS-related disability from tremor-related disability. Nonpharmacologic methods used in essential tremors, such as weighted utensils and cutlery, are an option in aiding activities of daily living. Cooling the limb before activities involving precision movements such as signing documents or applying makeup has been proposed as an alternative option.

Medications used for MS tremors include isoniazid, which has been shown in 2 randomized controlled trials to improve both the postural and intention components of the MS tremor. However, relatively high doses up to 1200 mg/d were needed, and this was associated with multiple side effects such as drowsiness, elevated liver function tests, and anorexia. Animal studies have suggested a role for cannabis in improving tremor in experimental models of allergic autoimmune encephalomyelitis. However, a randomized controlled trial did not demonstrate any significant benefit. In a case report, 4-aminopyridine was found to be useful in MS tremor, possibly because of its effects in improving the excitability and precision of cerebellar Purkinje cells.

Topiramate has also been used successfully at low doses of 50 mg/d to control MS tremor and improve function. A randomized, double-blind, placebo-controlled trial of botulinum toxin was found to reduce the severity of MS-related tremor and tremor-related disability, although a mild to moderate degree of weakness was noted in patients receiving botulinum toxin. Although case series and crossover studies showed a possible role for levetiracetam in MS tremor, a randomized double-blind study failed to show any significant benefits. Other medications tried include ondansetron, which has shown equivocal results, and primidone, which showed some benefit in a pilot study wherein improvement was noted in the activities of daily living, Fahn Tremor rating scale, and nine-hole peg test in the treatment group.

Surgical options for tremor in MS include lesional surgery and deep brain stimulation (DBS). Traditional targets have included the ventral intermediate and ventral oralis posterior nuclei of the thalamus. More recently, other targets such as the zona incerta and subthalamic nucleus have also been studied. A systematic review of DBS in MS tremor showed improvement in tremors in up to 87% of patients, although the benefits did not appear to persist over time and reprogramming was needed. Improvement in quality of life has been harder to demonstrate because of difficulties in distinguishing between MS-related disability and tremor-related disability. On rare occasions, permanent tremor reduction has been noted after DBS. Such reduction can occur in the setting of weakness or independent of weakness, suggesting that this is either the natural progression of MS or a possible demyelinating “lesion effect” from long-term stimulation. One review concluded that thalamic stimulation with DBS and thalamotomy were comparable in terms of the level of tremor control, with initial tremor suppression in 93.8% of patients undergoing thalamotomy and 96% in patients undergoing DBS. Functional improvement was noted more often in the thalamic stimulation group than in the thalamotomy group, and complications such as swallowing difficulties, dysarthria, hemiparesis, and balance problems were noted in both procedures.

Dystonias

Dystonia is an abnormal sustained muscle contraction causing twisting or turning around 1 or multiple joints. Paroxysmal dystonia, also referred to as tonic spasms, is the most frequently reported type of dystonia in MS. This condition consists of involuntary muscle contractions of a limb or unilateral limbs that cause painful, stereotyped posturing or movements. It differs from other types of dystonia in that the movements are not sustained. Instead, attacks are brief (seconds to a few minutes) and occur several times a day. The proposed pathophysiologic explanation is ephaptic activation of axons secondary to a demyelinating lesion. In cases where imaging correlation has been available, lesions have been found in the midbrain, posterior limb of the internal capsule, cerebral peduncle, thalamus, subthalamus, and cervical spinal cord. Although the causative lesions theoretically could occur anywhere along the motor pathway, it is most likely that the spasms would be generated from sites where the motor fibers run very closely together. Treatment options include a course of high-dose steroid therapy, carbamazepine, acetazolamide, and valproate.

Cervical dystonia, also called spasmodic torticollis, is a focal dystonia affecting the neck muscles that leads to abnormal movements of the head and sustained and often painful postures of the head, neck, and shoulders. It has been infrequently reported in MS patients. Some investigators view cervical dystonia and MS as coincidental diseases. In 2 of the more recent case reports, a causative relationship was thought most likely. In one case, this was based on lesions in the high cervical spine identified on magnetic resonance imaging (MRI), and in the other, on the patient’s response to corticotropin. A sensible course of treatment for a patient with known MS presenting with cervical dystonia would be to start with a course of high-dose steroids and then, if symptoms are still present, to treat with botulinum toxin.

Occasionally, generalized dystonia and other focal dystonias, such as writer’s cramp, have been reported in MS patients. Investigators have variously postulated that the dystonia was coincidental to or caused by the MS.

Parkinsonism

Parkinsonism is a term that refers to a combination of signs seen in Parkinson disease, including bradykinesia, tremor, rigidity, and postural instability. Although parkinsonism occurs rarely in patients with MS, there are several case reports of this phenomenon. However, investigators are divided as to whether the diseases are coincidental or whether MS lesions actually cause the parkinsonism. It is likely that both scenarios occur. Clinical evidence in favor of a causative relationship includes the presence of MRI lesions in the midbrain or basal ganglia, and improvement with use of steroids. Coincidental cases tend to lack such features, and patients tend to improve with levodopa therapy.

Restless limbs syndrome

Restless limbs syndrome (RLS) is a distressing desire to move the limbs, usually the legs, while sitting or lying down. Symptoms are relieved by walking. Symptoms worsen in the evening, and periodic limb movements may occur during sleep. RLS is common, with a prevalence of 5% to 15%. Some studies have shown a higher prevalence of RLS in MS patients, whereas others did not find any association. A recent large, prospective, population-based study found a significantly higher prevalence of RLS in women with MS than in women without MS: 15.5% versus 6.4%. There was also a significant difference in women reporting symptoms classified as “severe RLS” when compared with women without MS: 9.9% versus 2.6%. There are different theories on the pathophysiologic link between MS and RLS. One small study showed more cervical spinal cord lesions in MS patients with RLS compared with those without RLS. Iron deficiency is also associated with RLS. Several studies have found a higher prevalence of iron deficiency anemia in MS patients than in controls, and one study noted a stronger association between RLS and MS in premenopausal than in postmenopausal women, drawing the implication that the premenopausal women likely have lower iron levels attributable to menstrual blood loss. A ferritin level should be checked in RLS patients, and iron replacement considered for a ferritin level lower than 50 μg/L. Identifying and treating RLS in MS patients is important because patients often have difficulty falling asleep; patients will then contend with both daytime sleepiness and the fatigue of MS. Dopamine agonists, such as ropinirole, pramipexole, and transdermal rotigotine are effective treatments for RLS. Other options include carbidopa-levodopa, clonazepam, or gabapentin.

Chorea and ballismus

Chorea, meaning “dance” in Greek, resembles exaggerated fidgetiness. The movements are usually generalized and purposeless. In mild cases, chorea may be blended into natural movements and appear purposeful. Chorea has very rarely been reported in MS patients. In some of these cases, the investigators deduced there was a causal association. For example, one patient with relapsing remitting MS developed widespread, bilateral chorea, and brain MRI showed bilateral involvement near the caudate nuclei. Treatment options include benzodiazepines, tetrabenazine, and neuroleptic medicines such as risperidone, olanzapine, haloperidol, and fluphenazine.

Ballismus is a large-amplitude, proximal chorea, typically causing the affected limb to fling violently. It usually occurs acutely on one side of the body and is referred to as hemiballismus. It is caused most commonly by infarct in the contralateral subthalamic nucleus. There are several reported cases of hemiballismus in MS patients. On MRI, MS plaques were seen in the contralateral subthalamic nucleus in some of these patients. Treatment options are the same as for chorea, although it would be reasonable to first try a course of steroids.

Myoclonus

Myoclonus is a sudden, brief muscle contraction. Myoclonus can localize to the cortex, subcortex, brainstem, spinal cord, and, in rare cases, the peripheral nervous system. Myoclonus is rarely reported in MS. Palatal myoclonus is the most commonly reported type. Palatal myoclonus is thought to localize to lesions in the dentato-rubro-olivary pathway. In one patient with bilateral palatal myoclonus, MRI showed plaques in the pons. Most MS patients with palatal myoclonus are also noted to have nystagmus. Other reported cases of myoclonus in MS patients are intention myoclonus and propriospinal myoclonus. Pharmacologic treatment is the same as is recommended for myoclonus from other causes. Commonly used medications include valproic acid, clonazepam, and levetiracatem. For palatal myoclonus botulinum toxin may be effective.

Tics

Tics are temporarily suppressible, abnormal movements or vocalizations. The association between MS and tics is extremely rare. There has been one case report of a simple phonic tic, one of a complex vocal tic, and recently a report of Tourettism, which was thought to be caused by the patient’s secondary progressive MS. The causative link between tics and MS is difficult to make, both because of the dearth of cases that have been reported and because the precise anatomic localization of tics is not established. However, basal ganglia and the cortico-striato-thalamocortical circuit are thought to be involved, and lesions were seen in those areas in the few cases reported. Tics that are troublesome to the patient can be treated with clonidine, neuroleptic agents, benzodiazepines, or tetrabenazine.

Abnormal facial movements

Hemifacial spasm (HFS) is a syndrome of intermittent or sustained unilateral facial contraction that can be caused by compression of posterior fossa structures by ectatic vessels or tumors. In essential HFS there is no compressive lesion. HFS is occasionally seen in MS patients. In one case series of 6 MS patients who developed HFS, 2 of the patients had brain MRI showing lesions in the lower pons unilateral to the HFS. The investigators posit that in MS patients with HFS, the lesions usually involve the facial nucleus or the proximal portion of the facial nerve. Treatment options for HFS in MS patients include corticosteroids, carbamazepine, and especially botulinum toxin.

Spastic paretic hemifacial contracture (SPHC) is a sustained unilateral contraction of the facial muscles with ipsilateral facial paresis. The condition was originally associated with brainstem tumors, but there have been a handful of case reports of SPHC in MS patients. MRI in those cases showed pontine lesions, and symptoms resolved over a few months. SPHC is distinguishable from facial myokymia, which also occurs in MS patients, by the absence of myokymia on both examination and electromyography, and clinically there is more severe contracture in SPHC.

Facial myokymia is a continuous wave-like, undulating and flickering movement affecting individual muscle fascicles. Facial myokymia has been frequently reported in MS patients, including reports of this as the presenting sign of MS. It is thought to localize to the pontine tegmentum, specifically the postnuclear, postgenu portion of the facial nerve. The most effective treatment is botulinum toxin.

Ataxia

Ataxia refers to impaired motor coordination that is usually related to disorders of the cerebellum or its connections with the rest of the central nervous system. Ataxia is a common movement disorder found in demyelinating disease, and can cause significant disability. It is characterized by dysfunction in coordination that can involve the limbs, trunk, and/or speech. Findings in ataxia include dysmetria, whereby there is impaired generation, guidance, and termination of the movement of a limb, causing overshoot or past-pointing. Ataxia can include abnormal postural reactions, causing rebound of a limb, and dysdiadochokinesis, whereby there is an inability to perform rhythmic repetitive movements such as rapid alternating hand movements. Ataxic speech is characterized by clumsy dysarthria that has altered rate, prosody, and modulation of speech. Coordination of eye movements is also often affected, resulting in nystagmus and hypometric or hypermetric saccades. An ataxic gait is wide-based and unstable, usually requiring slower and shorter strides. Ataxia can often be associated with kinetic and postural tremor.

Ataxia is usually localized to lesions or disorders involving the cerebellum or cerebellar projections to the brain, brainstem, thalamus, and spinal cord. Correlation of clinical symptoms to precise cerebellar anatomy has been difficult, but the most clinically useful anatomic divisions of the cerebellum are the midline, hemispheres, and posterior regions. The midline of the cerebellum, which includes the vermis, is associated with truncal ataxia, titubation, and gait ataxia. Unilateral limb ataxia is usually due to lesions in the ipsilateral cerebellar hemisphere. Lesions in the posterior cerebellum, which includes the flocculonodular lobe, can cause gait ataxia and balance problems as well as eye-movement dyscoordination such as nystagmus. Cerebellar tremor is often due to lesions that extend beyond the cerebellar cortex, involving the cerebello-rubro-thalamocortical tract. However, ataxia also has a significant component of sensory integration in coordinating movement, and a sensory ataxia can result from demyelinating lesions involving central or peripheral sensory tracts and the vestibular system.

Episodic ataxia has been reported in several patients in the context of demyelinating disease. Marcel and colleagues reported two patients presenting with gait ataxia and dysarthria as initial symptoms of demyelinating disease. Both patients had midbrain lesions at the level of the red nucleus, among other subcortical white-matter lesions. The first patient initially developed subacute gait ataxia and dysarthria following a mild upper respiratory infection. The ataxia resolved with high-dose intravenous steroid treatment, but the patient subsequently developed stereotyped episodes of gait ataxia, dysmetria, and dysarthria lasting 5 to 15 seconds and occurring up to 100 times per day. The patient had multiple nonenhancing T2-hyperintense lesions in the midbrain, including 1 at the level of the red nucleus, as well as in the periventricular and subcortical white matter. The episodes of ataxia remitted with another round of intravenous steroids and oral carbamazepine. This patient did not have further evidence of demyelinating disease in space and time, and was diagnosed with a clinically isolated syndrome. The second patient presented with similar episodes of paroxysmal dysarthria-ataxia as the initial presentation for MS. Again, his symptoms lasted 5 to 15 seconds, occurring up to 150 times per day, with a normal neurologic examination between episodes. This patient was also found to have several nonenhancing T2-hyperintense lesions in the periventricular white matter and midbrain at the level of the red nucleus, as well as in the pons, cerebellum, and cervical spinal cord. The paroxysmal ataxia and dysarthria resolved with oxcarbamazepine. Li and colleagues reported similar brief episodes of ataxia in two patients with demyelinating disease involving the red nucleus. Ataxic dysarthria was the presenting symptom in one of the patients, following an upper respiratory infection. Paroxysmal ataxia and dysarthria developed in the second patient after already being diagnosed with MS of 6 months’ duration. The episodes resolved with carbamazepine in both patients.

Karmon and colleagues reported 5 cases of limb ataxia associated with pericentral sulcus demyelinating lesions in MS. Three of the patients presented with limb ataxia as their first symptom of MS. All 5 patients had cortical and subcortical T2-FLAIR (fluid-attenuated inversion recovery) hyperintense lesions in the pericentral gyrus region contralateral to the limb ataxia without brainstem or cerebellar abnormality on MRI. Longitudinal follow-up of these patients ranging from 1.5 to 18 years revealed continued disability caused by the ataxic tremor, with 3 of the 5 patients with mild tremor, 1 with moderate tremor, and 1 with severe tremor. The patients had only partial improvement or no benefit from treatment with propranolol, benzodiazepines, levodopa, or primidone. Ataxic hemiparesis consistent with a lacunar syndrome has also been reported as a presenting symptom of MS, correlating with a hyperintense T2 lesion involving the thalamus and internal capsule contralateral to the limb ataxia. These cases underscore the variety of anatomic locations where demyelinating lesions can cause ataxia, beyond the previously well-recognized cerebellar projections to the basal ganglia and brainstem. These cases also illustrate the significant long-term disability that ataxia can cause in MS patients.

Symptomatic treatment of cerebellar ataxia remains challenging. Treatment is supportive and is often multidisciplinary. Benzodiazepines and barbiturates such as clonazepam and primidone, respectively, may initially improve tremor but can cause long-term worsening of balance and coordination. Baclofen has also been reported to worsen ataxia, whereas acetazolamide and calcium-channel blockers can be effective in episodic ataxias. Physical, occupational, and speech therapies, as well as rehabilitation, are important for maintaining safe ambulation and swallowing, and as much independence as possible with activities of daily living.

A systematic review of treatments for ataxia in MS identified 10 randomized controlled trials, none of which provided evidence for an effective long-term therapy for cerebellar tremor or ataxia. The included studies investigated isoniazid and pyridoxine, cannabis-based medications, baclofen, thalamotomy versus DBS, and physiotherapy and neurorehabilitation. Outcomes were complicated by various measurements of tremor, including videotaped tremor examination, accelerometry, surface electromyography, self-rating scales, balance time, and stance on a force plate. Identification of a significant improvement in ataxia outcomes was also limited by small sample size.

Ten patients with MS were included in a single, blinded, randomized controlled trial for treatment of medication-resistant tremor with thalamotomy and thalamic DBS. Both interventions initially improved tremor in all MS patients; however, the tremor returned in nearly all of the patients by 6 months after surgery and there was no improvement in disability scores at 6-month follow-up. There were also adverse effects in both thalamotomy and DBS treatment groups on gait, dysarthria, and arm ataxia.

Three randomized physiotherapy studies show modest improvement in function in MS patients with ataxia, although long-term benefits remain unclear. In a study of 26 secondary or primary progressive MS patients with significant ataxia randomized to physiotherapy with and without use of Johnstone pressure splints, both treatment arms had small improvement in limb stance time and step width following physiotherapy, and improvement in Expanded Disability Status Scale (EDSS) score of 0.5. There was no evidence for benefit from the use of Johnstone pressure splints. A study randomizing 23 patients to two different physiotherapy approaches found small improvement in Rivermead mobility index in both treatment arms. A third study randomized 42 patients with gait abnormalities to home, outpatient, or no therapy. Both the home and outpatient groups had improvement in Rivermead mobility index when compared with the group with no therapy. However, follow-up 2 months after treatment found that mobility had regressed to pretreatment levels. A case report of an MS patient with severe truncal ataxia describes torso-weighting as providing long-term benefit.

Topiramate was described in a case report to have long-term effectiveness on cerebellar tremor and ataxia. The reported patient had a 17-year history of well-controlled relapsing-remitting MS treated with natalizumab, with significant ataxia involving the trunk, limbs, eye movements, and speech, and severe postural and kinetic cerebellar tremor. She was unable to walk more than 50 ft (15 m) with bilateral support, or dress, bathe, or eat independently because of the severity of the tremor and ataxia. Her EDSS score was 6.5. MRI revealed a high lesion load with multiple white-matter lesions involving the pons, middle cerebellar peduncles, and cerebellar hemispheres. She responded to topiramate in a sustained, dose-dependent manner, titrated up to 150 mg/d. After 2 years of topiramate treatment, she had significant functional improvement and was able to eat, drink, and dress independently, and walk 600 ft (180 m) with a walking frame. Withdrawal of topiramate led to worsening of ataxia and tremor, which improved after restarting the medication.

Levetiracetam was found to improve cerebellar tremor in a small open-label pilot tolerability and efficacy study of 14 MS patients. Significant improvement was found on videotaped tremor and ataxia examination and the subjective Activities of Daily Life questionnaire after titration of levetiracetam. The medication was well tolerated, with 3 subjects withdrawing because of side effects of sedation or agitation. However, there have not yet been any further controlled, randomized studies looking at the efficacy of levetiracetam on ataxia in a larger number of MS patients.

In summary, ataxia is a common movement disorder in MS that can lead to significant disability. It is typically localized to lesions involving the cerebellum and cerebello-rubro-thalamocortical tract. However, reports have demonstrated that ataxia can be associated with lesions not involving the ipsilateral posterior fossa, such as the contralateral pericentral gyrus cortical and subcortical regions. Several case reports have highlighted a rare syndrome of brief episodic ataxia and dysarthria that can be found in the setting of demyelinating disease that is responsive to carbamazepine. Unfortunately, most ataxia is difficult to treat, and requires a multidisciplinary approach of physiotherapy, rehabilitation, and careful consideration of medications so as not to worsen it.