AETIOLOGICAL CLASSIFICATION OF TREMOR

Transcription

1 AIOLOGICAL CLASSIFICATION OF TREMOR M. H. Soad *, M. Z Md Zain, M. Hussein Department of Applied Mechanics and Design, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor Bahru, Malaysia. * Corresponding author: hafizsoad@gmail.com ABSTRACT This article reviews the activation conditions and aetiologies of tremor; as well as its diagnosis. Tremor is characterised as rhythmic and involuntary movement of body parts. There are several causes that would lead to tremor occurrence ranging from drug intake to neurological disorder such as Parkinson s disease. Tremor exhibited by the patient will have certain characteristics depending on causes. Identifying the tremor cause is crucial, as certain forms of treatment are compatible with only certain conditions. Usually tremor patients need to undergo clinical diagnosis that thoroughly analyzes patient s personal data. However, in some cases, the data alone is not enough to correctly distinguish the cause and hence patients require additional examination. However, the diagnosis could be very lengthy and costly. Hence, many researches are conducted under the initiative of assisting the diagnosis by developing a system to identify tremor causes mainly only from the tremor quantitative data; frequency and amplitude. Keywords: Classification, tremor, aetiology, diagnosis 1.0 INTRODUCTION Movement disorders are known as neurological syndromes which could either be hyperkinetic, hypokinetic, or both. Hyperkinetic is defined as the involuntary movement of body parts, and tremor is the most common type [1]. Definitively, tremor is a rhythmic and involuntary oscillation of body parts caused by the alternating contraction of the muscles [2-9]. The most common parts of the body where the tremor is visible or affected are the hands. Tremor could occur in two different conditions known as resting and action depending on the aetiology. Rest tremor is the condition in which the tremor occurs in the body part even as it is fully supported against gravity such as placing the arm on top of a table [3]. Figure 1 shows the picture of a person his hands on top of a table representing the rest condition. This kind of tremor condition usually occurs with Parkinson s Disease (PD) patients. As for action tremor, the tremors are produced when there is any voluntary movement of the muscle which involves contraction, and it could be further divided into five different condition known as postural, kinetic, intention, task specific and isometric [4]. 14

2 Figure 1: Picture of hands placed on top of a table (Rest condition). Postural tremor is a condition in which the tremor occurs as the body parts or limbs are maintained in a position such that the affected parts are suspended against gravity. An example of postural position is the position where the arm is stretched away from the body and maintained parallel to the ground for a certain period of time such as in Figure 2. Kinetic tremor, on the other hand, is tremor which occurs during any kind of voluntary movement and; almost similar to intention tremor, which occurs in voluntary movements which are target directed and the tremors intensify as the movement gets closer to the target. An example of intention tremor is the motion of touching the tip of our nose, such as in Figure 3 and as the hand gets closer to the nose; the tremor will start to amplify. The next condition of tremor is the task specific tremor which only occurs during certain tasks which require more skill, such as writing. The last tremor condition is the isometric tremor which is the result of the muscle contraction against a stationary and rigid object such as the picture in Figure 4. 15

3 Figure 2: Picture of hand stretched forward (Postural condition). Figure 3: Picture of simulated motion of touching the tip of nose (Intention condition). 16

4 Figure 4: Picture of simulated motion of pressing top of table with hands (Isometric condition). 2.0 AIOLOGY OF TREMOR The tremor origins can be divided into two types, known as physiologic tremor and pathologic tremor. Physiologic tremor (PT) occurs in every healthy person and commonly occurs during postural movement [2, 4, 10, 11]. Physiologic tremor is characterised as very fine tremor which occurs at the frequency of 8 12 Hz. Pathologic tremor is the tremor which is caused by motor impairment such as PD and drug intake [12]. Enhanced physiologic tremor (EPT) is the alleviated form of physiologic tremor which is caused by anxiety, muscle fatigue, metabolic disorder (such as thyroid), drug intake or the result of alcohol withdrawal [5, 10, 13]. Tremor patients can only be diagnosed for EPT if there is no presence of other neurological symptoms or diseases [14]. The characteristics of enhanced physiologic tremor are almost similar to the physiologic tremor, as it also occurs within the frequency range of 8-12 Hz and is usually triggered during postural condition. Even though EPT is almost similar with PT, the amplitudes of the tremor are different, as the amplitude for EPT is larger compared to PT. Among various types of movement disorders, Essential tremor () is the tremor most commonly triggered in postural and kinetic condition [6, 15]. Due to these commonly affected conditions, is usually defined as the movement disability during voluntary movement. The risk of having is influenced by four different factors which are age, ethnicity, family history of, and environment [16]. There is still risk of having despite being young, but the risk increases with age, as the number of people experiencing increases with the associated age. 17

5 often affects the upper limbs, as with most patients, affects the patients hands instead of the other body parts [17]. The tremor caused by is usually symmetrical as it affects both hands and forearms [3, 4]. The tremor usually occurs within the frequency range of 4 11 Hz [2]. Even though is known to occur in action condition, there are some cases where could also involve rest tremor. The main criteria for are the bilateral action tremor and absence of other neurological signs [15]. Annually, the frequency of tends to reduce as the tremor amplitude tends to intensify [18]. Parkinson s Disease (PD) is one type of parkinsonism and is the most commonly encountered, which leads to the upsurge of studies to further understand the cause, and come out with possible treatments [19]. Most PD patients experience three common symptoms; rest tremor, bradykinesia and rigidity. Rest tremor is the symptom where the person will experience tremor under the condition in which the affected body part is fully supported against gravity such as when placing the arm on top of a table [3]. The rest tremor experienced by PD patients occur at a frequency of 4 6 Hz with medium amplitude, and the rest tremor will vanish as the patients execute voluntary movement [1, 2]. However, about 60% of PD patients also suffer from postural tremor [4]. As for bradykinesia, it is the symptom in which the patientsexperience slowness in their movements especially in repeating or alternating manoeuvre [20, 21]. While rigidity represents the symptom in which any passive movement applied to a body part will be countered by some resistance, and usually identified by moving the patient s limb; the examiner will experience some increase in resistance during the movement [7, 19]. Tremor in PD originates from the degeneration of an area in the brain; specifically the degeneration of excitatory and inhibitory of dopaminergic neurons in the substantia nigra pars compacta which leads to the reduction of movement controlling chemical and as the result, PD will gradually become worse over time [2, 22]. Cerebellar Tremor (CT) is the intention tremor where the tremor appears during objective guided movement and the tremor intensity increases as the body part gets closer to the target [5, 23]. The intention tremor is caused by the delay of second and third phase of the triphasic EMG pattern, which in turn results in the stopping command to stop the body part movement executed too late, causing the motion to overshoot and this will repeat as the act of correcting the error is done [14]. The tremor could affect the patient s body either unilaterally or bilaterally depending on the cerebellar disease the patient suffers from. The tremor for this tremor group usually occurs with a frequency of less than 5Hz. CT arises from the lesion that occurs to the lateral cerebellar nuclei or superior cerebellar peduncle [2, 24]. Holmes Tremor (HT) usually comes in the form of rest tremor and intention tremor but in certain cases, postural tremor also occurs [3, 15]. HT was also formerly known asthalamic, midbrain or rubral tremor [25].HT is known to have the characteristic of irregular rhythm of the tremor and the tremor occurs at low frequency which is lower than 4.5 Hz [4, 10, 26]. HT usually affects the proximal limb rather than the distal. HT is suspected to originate from the lesions cerebellothalamic and nigrostriatal pathways [6]. 18

6 Dystonic Tremor (DT) is a type of tremor which occurs at the body parts which are affected by dystonia and it is recognizable through the abnormal posture resulting from dystonia [4]. DT is an action tremor where it could either occur during a postural condition or a kinetic movement of the affected body parts [5] and the tremor will diminish as the body parts are in resting condition [15]. Furthermore, DT also responsive to sensory trick where their condition will improve or the tremor diminishes as they perform a special manoeuvre such as touching their chin, eyelids, wrist of writing and many more [27, 28]. However, the sensory trick is different from one person to another; a manoeuvre that is effective with one patient is not necessarily applicable to another. This type of tremor is characterised to have irregular amplitudes and variable frequencies of about 4 8 Hz [1]. Orthostatic Tremor (OT) is a high frequency tremor that affects the patient s leg when standing, and can produce a feeling of unsteadiness [5, 6, 29]. There are some studies which suggest that the tremor is caused by the central generator which is located in the posterior fossa and it is possible to stop the tremor by applying electrical stimulation at the posterior fossa region [30, 31]. The frequency of OT is about Hz and tends minimize as the patients execute walking motion [10]. This high frequency tremor is much easier to notice by palpation than by sight due to the fine amplitude produced. Neuropathic Tremor (NT) is the result of peripheral neuropathy where the peripheral nervous system which is responsible in transmitting the information from the brain or the spinal cord to the rest of the body is damaged [4, 5. 23, 32]. The NT mostly affects the arms with frequency of 3 6 Hz in postural and kinetic condition but there are also some reports which mention the presence of rest component [1]. Palatal Tremor is characterised as the tremor that occurs on a muscle situated in the mouth called the soft palate [5, 6, 10, 26]. The tremor produced is in the frequency range of less than 6 Hz [1]. This type of tremor is as not disabling as the other types as the patient is only sometimes bothered by ear click resulting from the tremor. 3.0 CLASSIFICATION AND DIAGNOSIS OF TREMOR The aetiology of tremor exhibited by patients are clinically diagnosed based on the patient s history, phenomenology of the tremor, frequency and amplitude of tremor; and neurological examination [7]. The patient s history comprises of how the tremor starts, history of patient s medication, the family history, presence of associated symptoms and; general and systemic examination. Certain phenomenology or activation conditions of the tremor usually comes with certain types of tremor, such as PD which usually comes with rest tremor, and could provide some hint to which disorder is responsible. The same goes with the frequency and amplitude data, even though there s overlapping range between certain groups of tremor. In some cases, the clinical diagnoses are insufficient to accurately identify the tremor aetiology, and further examination is required [24]. Magnetic Resonance Imaging (MRI) tests 19

7 are able to identify whether the brain suffers from any structural defect [33], such as through pointing out the enlargement of inferior olivary nucleus for palatal tremor [10]. Positron emission tomography (P) and single-photon emission computed tomography (SPECT) are other tools used to confirm the diagnosis of PD patients as this imaging is capable of providing information regarding changes in striatal dopamine levels [34, 35]. There are also several other tools used in clarifying the tremor diagnosis depending on the suspected tremor aetiology after the clinical assessment. However, sometimes the diagnosis on tremor patients is difficult, time consuming and costly; a few steps have been taken by some researchers to develop a classification system with the aim to assist in diagnosing tremor patients, and could possibly speed up the identification process. Table 1 summarises some of researches done previously to assist in tremor diagnosis. These researchers have developed algorithms to classify the tremor based on the quantitative data obtained from accelerometer, electromyogram, or both. Table 1: Summary of previous tremor classification researches. Author Classified Tremor Ai et al. [36] PD PT Methodology and Findings Found that more than 90% of the signal from PD and patients are non gausian and non linear All the signals obtained go through bispectrum analysis (due to compatibility with non gausian data) to obtain the three largest amplitudes. The analysed signals are run through Back-Propagation Neural Network of 15 layer neurons. Accuracy 92.9% Engin et al. [37] PD PT Used linear prediction coefficients, wavelet transform - based entropy and variance values, higher-order cumulants, and power ratio. Scaled-conjugate (SCG) and BFGS (Broyden Fletcher Goldfarb Shanno) gradient learning algorithms were used in back-propagation based on multilayer perceptron network structure. -BFGS (91.02%) had higher accuracy if compared to SCG (88.48%). 91.0% 20

8 Ai et al. [38] PD PT Signal features are extracted using three different methods: bispectrum, empirical mode decomposition (EMD) and discrete wavelet transform (DWT). Extracted features are run through three separate independent BPNN and results are combined using Dempster-shafer (D-S) evidence theory. 96.7% Muthuraman et al. [39] PD Found that the mean power for harmonic peak can be used to distinguish between and PD. Among 12 patients with unclear tremor type, the method was capable of accurately distinguishing 11 out of 12 patients. 94.0% Machowska- Majchrzak et al. [40] PD CT PT Study on the relationship between the asymmetry of pathological tremor and the tremor intensity, frequency, centre frequency, standard deviation of centre frequency and harmonic index. Results of the study show that pathological tremors tend to be asymmetrical but not physiological tremors, and; PD had greatest asymmetry, while was found to have the largest tremor intensity. - Hossen et al. [41] PD Implemented Statistical Signal Characterization (SSC) technique and Receiver Operating Characteristic (ROC) for the classification. 90.0% Ayache et al. [42] PT Tremor is non stationary and changes with time but Fast Fourier transform (FFT) is suitable for signals which are periodic and stationary. This study introduces the use of the Hilbert Huang transform that combines EMD and Hilbert transform. - 21

9 Woods et al. [43] PT Used accelerometer and mobile phone as the test medium Implemented the task evaluation test which had the element of distraction and attention. Distraction task increased the tremor power of PD patients as compared to other task but not with. Support vector machine algorithm was used as the classifier. 96.4% Wile et al. [44] PT Proved that the performance of analogue accelerometer and smart watch with built-in accelerometer are almost the same. Used the threshold value obtained from Muthuraman M. et al (2011) for the classification criteria. 80.0% PD Parkinson s Disease; Essential Tremor; PT Physiologic Tremor; CT Cerebellar Tremor 4.0 CONCLUSION Accurate diagnosis of tremor patient is very crucial as different problems would require different types of treatment, and would not respond positively to the treatment of others. Furthermore, it is important to obtain the diagnosis results quickly, as there are types of tremor diseases that are not permanent and can be cured. In some cases, the tremor exhibited by the patient is unable to be completely identified through clinical diagnosis and requires additional examination with some sophisticated method that comes with high cost and a long duration of time. Many researches have been done with the goal of obtaining diagnosis results quickly and accurately by developing algorithms capable of assisting the diagnosis through the quantitative data of the tremor itself; frequency, and the amplitude. In conjunction with these efforts, a research will be conducted to develop a classification system capable of distinguishing a patient s tremor aetiology accurately among other tremor aetiologies. Acknowledgement The authors wish to thank the Universiti Teknologi Malaysia (UTM) for providing the funding and facilities to conduct this research. 22

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