Taking on Essential Tremor: New Tools and Approaches Offer patients Increased Treatment Options

Every year, Doris's primary care physician sends her to see a neurologist to check on her hand tremor, which has increasingly worsened over the past 20 years. Year in and year out, the neurologist asks her to draw a circle on a piece of paper. "The doctor looks at it, says 'Hmm,' and sends me home," Doris explains, adding that she gets no treatment, no recommendations, nothing except a request to schedule next year's appointment.

Robust controller for tremor suppression at musculoskeletal level in human wrist

Tremor is a rhythmical and involuntary oscillatory movement of a body part and it is one of the most common movement disorders. Orthotic devices have been under investigation as a noninvasive tremor suppression alternative to medication or surgery. The challenge in musculoskeletal tremor suppression is estimating and attenuating the tremor motion without impeding the patient's intentional motion. In this research a robust tremor suppression algorithm was derived for patients with pathological tremor in the upper limbs. First the motion in the tremor frequency range is estimated using a high-pass filter. Then, by applying the backstepping method the appropriate amount of torque is calculated to drive the output of the estimator toward zero. This is equivalent to an estimation of the tremor torque. It is shown that the arm/orthotic device control system is stable and the algorithm is robust despite inherent uncertainties in the open-loop human arm joint model. A human arm joint simulator, capable of emulating tremorous motion of a human arm joint was used to evaluate the proposed suppression algorithm experimentally for two types of tremor, Parkinson and essential. Experimental results show 30-42 dB (97.5-99.2%) suppression of tremor with minimal effect on the intentional motion.

Online tremor suppression using electromyography and low-level electrical stimulation

Tremor is one of the most prevalent movement disorders. There is a large proportion of patients (around 25%) in whom current treatments do not attain a significant tremor reduction. This paper proposes a tremor suppression strategy that detects tremor from the electromyographic signals of the muscles from which tremor originates and counteracts it by delivering electrical stimulation to the antagonist muscles in an out of phase manner. The detection was based on the iterative Hilbert transform and stimulation was delivered above the motor threshold (motor stimulation) and below the motor threshold (sensory stimulation). The system was tested on six patients with predominant wrist flexion/extension tremor (four with Parkinson disease and two with Essential tremor) and led to an average tremor reduction in the range of 46%-81% and 35%-48% across five patients when using the motor and sensory stimulation, respectively. In one patient, the system did not attenuate tremor. These results demonstrate that tremor attenuation might be achieved by delivering electrical stimulation below the motor threshold, preventing muscle fatigue and discomfort for the patients, which sets the basis for the development of an alternative treatment for tremor.

Evaluation of a wearable orthosis and an associated algorithm for tremor suppression

We describe a wearable orthosis and an associated algorithm for the simultaneous assessment and treatment of essential tremor, one of the most common movement disorders in humans involving an overactivity of the olivo-cerebellar pathways. A motor providing effective viscosity is fixed on a wearable orthosis in the upper limbs. The motor is controlled by a personal computer with software processing in real time the position and rate of rotation of the joint detected by a chip gyroscope. The orthosis can be used in a monitoring mode and in an active mode. The range of tremor suppression of the signals above the orthosis operational limit ranges from about 3% (percentile 5) to about 79% (percentile 95) in relation to energy in the monitoring mode. Considering both postural and kinetic, the mean tremor energy decreased from 55.49 +/- 22.93 rad2 s(-3) in the monitoring mode to 15.66 +/- 7.29 rad2 s(-3) in the active mode. Medians of power reduction were below 60% for the wrist and the elbow. In addition to supplying new information on the interactions between kinematics, dynamics and tremor genesis, this non-invasive technique is an alternative to current therapies. This new approach will provide new insights into the understanding of motor control.

Identification of target areas for deep brain stimulation in human basal ganglia substructures based on median nerve sensory evoked potential criteria

OBJECTIVE

In the interventional treatment of movement disorders, the thalamic ventral intermediate nucleus (VIM) and the subthalamic nucleus (STN) are the most relevant electrode targets for deep brain stimulation (DBS). This study tested the value of somatosensory evoked potentials (SEP) for the functional identification of VIM and STN.

METHODS

Median nerve SEP were recorded from the final stimulation electrodes targeted at STN and VIM. Throughout the stereotactic procedure SEP were recorded during short electrode stops above STN/VIM and within the presumed target areas. After digital filtering, high and low frequency SEP components were analysed separately to parameterise both the 1000 Hz SEP burst and low frequency (<100 Hz) components.

RESULTS

SEP recorded in the VIM target region could unequivocally be distinguished from SEP recorded in STN. The 1000 Hz burst signal was significantly larger in VIM than in STN without any overlap of amplitude values. In the low frequency band, a primary high amplitude negativity was obtained in VIM, contrasting with a low amplitude positivity in STN. SEP waveshapes in recordings above target positions resembled SEP obtained in STN. When entering VIM, a sharp amplitude increase was observed over a few millimetres only.

CONCLUSIONS

Based on SEP criteria, the VIM target but not the STN region can be identified by typical SEP configuration changes, when penetrating the target zone. The approach is independent of the patient's cooperation and vigilance and therefore feasible in general anaesthesia. It provides an easy, reliable, and robust tool for the final assessment of electrode positions at the last instance during electrode implantation when eventual electrode revisions can easily be performed.

A novel quality of life instrument for deep brain stimulation in movement disorders

OBJECTIVE

To develop a short instrument to examine quality of life (QoL) which specifically addresses patients with movement disorders treated by deep brain stimulation (DBS).

DESIGN

The instrument was developed within an existing concept of a modular questionnaire (questions on life satisfaction: "general life satisfaction" QLS(M)-A, and "satisfaction with health" QLS(M)-G), in which each item is weighted according to its relative importance to the individual.

METHODS

Items were generated by interviews with 20 DBS patients, followed by item reduction and scale generation, factor analysis to determine relevant and final questionnaire items, estimation of reliability, and validation based on the medical outcome study 36 item short form health survey (SF-36) and the EuroQol (EQ-5D) (data from 152 patients with Parkinson's disease, essential tremor, or idiopathic torsion dystonia, including 75 patients with DBS).

RESULTS

Initial questionnaires were reduced to 12 items for a "movement disorder module" (QLS(M)-MD), and five items for a "deep brain stimulation module" (QLS(M)-DBS). Psychometric analysis revealed Cronbach's alpha values of of 0.87 and 0.73, and satisfactory correlation coefficients for convergent validity with SF-36 and EQ-5D.

CONCLUSIONS

QLS(M)-MD and QLS(M)-DBS can evaluate quality of life aspects of DBS in movement disorders. Psychometric evaluation showed the questionnaires to be reliable, valid, and well accepted by the patients.

Functional outcomes after gamma knife thalamotomy for essential tremor and MS-related tremor

Twelve patients with a median age of 75 years underwent gamma knife thalamotomy for essential tremor (ET) (n = 9) or MS-related tremor (n = 3). All 11 evaluable patients noted improvement in action tremor. Six of eight ET patients had complete tremor arrest, and the violent action tremor in all three patients with MS was improved. One patient developed transient arm weakness. Stereotactic radiosurgery for ET and MS-related tremor is safe and effective for patients who may be poor candidates for other procedures.