Upper limb intention tremor assessment: opportunities and challenges in wearable technology

BACKGROUND

Tremors are involuntary rhythmic movements commonly present in neurological diseases such as Parkinson's disease, essential tremor, and multiple sclerosis. Intention tremor is a subtype associated with lesions in the cerebellum and its connected pathways, and it is a common symptom in diseases associated with cerebellar pathology. While clinicians traditionally use tests to identify tremor type and severity, recent advancements in wearable technology have provided quantifiable ways to measure movement and tremor using motion capture systems, app-based tasks and tools, and physiology-based measurements. However, quantifying intention tremor remains challenging due to its changing nature.

METHODOLOGY & RESULTS

This review examines the current state of upper limb tremor assessment technology and discusses potential directions to further develop new and existing algorithms and sensors to better quantify tremor, specifically intention tremor. A comprehensive search using PubMed and Scopus was performed using keywords related to technologies for tremor assessment. Afterward, screened results were filtered for relevance and eligibility and further classified into technology type. A total of 243 publications were selected for this review and classified according to their type: body function level: movement-based, activity level: task and tool-based, and physiology-based. Furthermore, each publication's methods, purpose, and technology are summarized in the appendix table.

CONCLUSIONS

Our survey suggests a need for more targeted tasks to evaluate intention tremors, including digitized tasks related to intentional movements, neurological and physiological measurements targeting the cerebellum and its pathways, and signal processing techniques that differentiate voluntary from involuntary movement in motion capture systems.

Clinical Heterogeneity of Essential Tremor: Understanding Neural Substrates of Action Tremor Subtypes

Essential tremor (ET) is a common movement disorder affecting millions of people. Studies of ET patients and perturbations in animal models have provided a foundation for the neural networks involved in its pathophysiology. However, ET encompasses a wide variability of phenotypic expression, and this may be the consequence of dysfunction in distinct subcircuits in the brain. The cerebello-thalamo-cortical circuit is a common substrate for the multiple subtypes of action tremor. Within the cerebellum, three sets of cerebellar cortex-deep cerebellar nuclei connections are important for tremor. The lateral hemispheres and dentate nuclei may be involved in intention, postural and isometric tremor. The intermediate zone and interposed nuclei could be involved in intention tremor. The vermis and fastigial nuclei could be involved in head and proximal upper extremity tremor. Studying distinct cerebellar circuitry will provide important framework for understanding the clinical heterogeneity of ET.

Radiofrequency Ablation of Prelemniscal Radiations for the Treatment of Non-Parkinsonian Tremor

OBJECTIVE

Previous reports proposed prelemniscal radiations (Raprl) as a target to treat motor symptoms of Parkinson's disease, and this was found particularly effective to control rest and postural tremor. However, tremor of other etiologies has been seldom treated with deep brain stimulation or ablation in this target. We present a series of such cases successfully treated by Raprl radiofrequency (RF) lesions.

MATERIAL AND METHODS

Six patients with predominant unilateral tremor on the right arm: 4 intention, 1 cerebellar and 1 rubral tremor, incapacitating in spite of at least 2 regimes of medical treatment at maximal tolerated doses, were operated under local anesthesia. RF lesions were performed in Raprl contralateral to most prominent symptoms. Patients had monthly evaluation of tremor severity through the Fahn-Tolosa-Marin Tremor Rating Scale and disability through the Tremor Disability Scale along a 1-year follow-up.

RESULTS

In 4/6 patients tremor was stopped by the simple insertion of an RF electrode in Raprl; in the other 2 cases, stimulation through the RF electrode at 100 Hz, with 100 µs and 1.0-1.5 V, stopped the tremor without side effects. Tremor disappeared in all cases immediately after surgery and partially reappeared in 2 cases with an amplitude about 20% of the preoperative condition. RF lesions in postoperative MRI ranked from 1.8 to 2.6 mm in diameter.

CONCLUSIONS

RF lesioning in Raprl is a simple, highly effective, inexpensive way to treat tremor of different etiologies.

Clinical and Genetic Evaluation of Spinocerebellar Ataxia Type 10 in 16 Brazilian Families

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant disorder in which patients have a slowly progressive cerebellar ataxia, with dysarthria, dysphagia, and epilepsy. The aims of this study were to characterize the phenotypic expression of SCA10 and to examine its genotype-phenotype relationships. Ninety-one Brazilian patients with SCA10 from 16 families were selected. Clinical and epidemiological data were assessed by a standardized protocol, and severity of disease was measured by the Scale for the Assessment and Rating of Ataxia (SARA). The mean age of onset of symptoms was 34.8 ± 9.4 years. Sixty-two (68.2%) patients presented exclusively with pure cerebellar ataxia. Only 6 (6.6%) of the patients presented with epilepsy. Patients with epilepsy had a mean age of onset of symptoms lower than that of patients without epilepsy (23.5 ± 15.5 years vs 35.4 ± 8.7 years, p = 0.021, respectively). All cases of intention tremor were in women from one family. This family also had the lowest mean age of onset of symptoms, and a higher percentage of SCA10 cases in women. There was a positive correlation between duration of disease and severity of ataxia (rho = 0.272, p = 0.016), as quantified by SARA. We did not find a statistically significant correlation between age of onset of symptoms and expansion size (r = - 0.163, p = 0.185). The most common clinical presentation of SCA10 was pure cerebellar ataxia. Our data suggest that patients with epilepsy may have a lower age of onset of symptoms than those who do not have epilepsy. These findings and the description of a family with intention tremor in women with earlier onset of symptoms draw further attention to the phenotypic variability of SCA10.

Revisiting the Clinical Phenomenology of "Cerebellar Tremor": Beyond the Intention Tremor

Tremor is an involuntary, rhythmic, oscillatory movement of a body part. It is a central feature of a range of diseases resulting from pathological changes in the cerebellum. Interestingly, in modern times, the terms "cerebellar tremor" and "intention tremor" are often used synonymously and interchangeably. However, "cerebellar tremor" (i.e., tremors of cerebellar origin) do not always present exclusively as intention tremor. In this article, we comprehensively revisit the clinical phenomenology of tremors observed in various diseases that are based in the cerebellum. By this, we mean diseases for which the cerebellum and its various connections are often seen as playing a central and defining role. These include spinocerebellar ataxias, essential tremor, orthostatic tremor, dystonia, acute cerebellitis, cerebellar tumors, paraneoplastic cerebellar degeneration, and cerebellar strokes. The theme of this article is to highlight, through published data available in the current literature, that the clinical phenomenology of tremor of cerebellar origin is heterogeneous, and it extends beyond that of intention tremor to include postural tremors, kinetic tremor, rest tremor, and orthostatic tremor. This heterogeneity is consistent with the seminal work of Gordon Holmes, in which he described a variety of tremors aside from intention tremor in the setting of cerebellar lesions. In the end, it would seem that the notion that intention tremor is the sole signature of cerebellar lesions is an over-simplification and is not correct. Future studies are warranted to identify and further characterize the heterogeneity of tremors arising from the various cerebellar etiologies.

Movement Disorders in Non-Wilsonian Hepatic Cirrhotic Patients: The Subgroup Analysis of Various Phenotypes and Associated Risk Factors

Objective

The aim of this subgroup analysis was to identify the risk factors associated with the development of various movement disorder phenotypes.

Methods

Eighty-three non-Wilsonian cirrhotic patients with abnormal movements were allocated into the following groups: intention tremor, bradykinesia, Parkinsonism, and abnormal ocular movements. These movement types were considered the primary outcomes as there was a sufficient sample size. Researchers took into consideration the gender, etiologies of cirrhosis, cirrhosis-related complications, hepatic encephalopathy, medical illness, and some neurological deficits as potential factors associated with these movement disorders.

Results

The male gender (p = 0.002) and alcoholic cirrhosis (p = 0.005) were significant factors for the prevalence of intention tremors. In bradykinesia, hepatic encephalopathy was highly statistically significant (p < 0.001), and females more commonly developed bradykinesia (p = 0.04). The Parkinsonism features in this study were confounded by hyperlipidemia (p = 0.04) and motor or sensory deficits (p = 0.02). Jerky pursuits and a horizontal nystagmus were detected. Jerky pursuits were significantly related to hepatic encephalopathy (p = 0.003) and bradykinesia, but there were no factors associated with the prevalence of nystagmus other than an intention tremor.

Conclusions

The association of alcoholic cirrhosis with the development of intention tremor indicates that the persistent cerebellar malfunction in cirrhotic patients is due to alcohol toxicity. The slowness of finger tapping and jerky pursuit eye movements are significantly associated with hepatic encephalopathy. Thus, further studies are needed to evaluate the diagnostic value of these two signs for an early detection of mild hepatic encephalopathy.

Movement Disorders in Non-Wilsonian Cirrhotic Patients: A Report of the Prevalence and Risk Factors from a Study Done in a Medical School in an Agricultural-Based Community

Objective

Parkinsonism and other movement disorders have previously been reported in the acquired hepatocerebral degeneration associated with portosystemic shunting. However, there is no study to date about their prevalence as has been noted in general practice.

Methods

One hundred and forty-three patients with hepatic cirrhosis from the gastroenterology clinic and internal medicine wards were enrolled. Liver data included the diagnoses, etiologies, assessments of complications, and treatments for cirrhosis. Hepatic encephalopathy was classified with regard to the West Haven criteria for semi-quantitative grading for mental status. Neurological examination results and abnormal involuntary movements were recorded as primary outcomes. Neuro-radiology was used for the detection of severe brain lesions.

Results

Alcoholism was the most common cause of liver cirrhosis. Eighty-three patients (58%) presented with movement disorders. Asterixis was found in one of the cases. The most common movement disorder seen was an intentional tremor at 37.1%, which was followed by bradykinesia, Parkinsonism, and postural tremors at 29.4%, 10.5%, and 6.3%, respectively. The prevalence of movement disorders simultaneously increased with a high Child-Turcotte-Pugh score. The hepatic encephalopathy was grade 1 and 2. With the inclusion of age-range adjustments, we found that alcoholic cirrhosis and hepatic encephalopathy are statistically significant factors [p < 0.05, odds ratio (OR) = 6.41, 95% confidence interval (CI) 1.38–29.71 and p < 0.001, OR = 13.65, 95% CI 4.71–39.54] for the development of movement disorders in non-Wilsonian cirrhotic patients.

Conclusions

Intentional tremor is a common abnormal movement. Alcoholic cirrhosis and hepatic encephalopathy are significant risk factors in the development of movement disorders in non-Wilsonian cirrhotic patients.

Identification of two novel KIF5A mutations in hereditary spastic paraplegia associated with mild peripheral neuropathy

Spastic paraplegia type 10 (SPG10) is a rare form of autosomal dominant hereditary spastic paraplegia (AD-HSP) due to mutations in KIF5A, a gene encoding the neuronal kinesin heavy-chain involved in axonal transport. KIF5A mutations have been associated with a wide clinical spectrum, ranging from pure HSP to isolated peripheral nerve involvement or complicated HSP phenotypes. Most KIF5A mutations are clustered in the motor domain of the protein that is necessary for microtubule interaction. Here we describe two Spanish families with an adult onset complicated AD-HSP in which neurological studies revealed a mild sensory neuropathy. Intention tremor was also present in both families. Molecular genetic analysis identified two novel mutations c.773 C>T and c.833 C>T in the KIF5A gene resulting in the P258L and P278L substitutions respectively. Both were located in the highly conserved kinesin motor domain of the protein which has previously been identified as a hot spot for KIF5A mutations. This study adds to the evidence associating the known occurrence of mild peripheral neuropathy in the adult onset SPG10 type of AD-HSP.

Giant middle fossa epidermoid presenting as holmes' tremor syndrome

Intracranial dermoids may gradually reach an enormous size before the onset of symptoms. Common clinical presentations of intracranial epidermoid include headache and seizures. We present a case of a 35-year female patient with giant middle fossa epidermoid that presented with Holmes’ tremor syndrome, and we review the relevant literature. To the best of our knowledge, such a presentation has not previously been described in the literature.

Thalamic physiology of intentional essential tremor is more like cerebellar tremor than postural essential tremor

The neuronal physiological correlates of clinical heterogeneity in human essential tremor are unknown. We now test the hypothesis that thalamic neuronal and EMG activities during intention essential tremor are similar to those of the intention tremor which is characteristic of cerebellar lesions. Thalamic neuronal firing was studied in a cerebellar relay nucleus (ventral intermediate, Vim) and in a pallidal relay nucleus (ventral oral posterior, Vop) during stereotactic surgery for the treatment of tremor. Nine patients with essential tremor were divided clinically into two categories: one with a substantial component of tremor with intention (termed intention ET) and the other without (postural ET). These types of essential tremor were compared with patients having intention tremor plus other clinical signs of cerebellar disease (cerebellar tremor). Neurons in patients with either intention ET or cerebellar tremor had lower firing rates and lower spike×EMG coherence than those in patients with postural ET. Patients with intention ET had a lower spike×EMG phase lead than those with postural ET. Overall, thalamic activity measures of intention ET were different from postural ET but not apparently different from those of cerebellar tremor. One patient with the intention ET (number 4) had a good response to a left thalamotomy and then suffered a right cerebellar hemispheric infarct five years later. After the stroke the intention ET recurred, which is consistent with our hypothesis that intention ET is similar to that of the intention tremor which is characteristic of cerebellar lesions.