1Department of Neurology, Gyeongsang National University Hospital, Jinju, Korea
2Department of Neurology, Gyeongsang National University College of Medicine, Jinju, Korea
Corresponding author: Heeyoung Kang, MD, PhD Department of Neurology, Gyeongsang National University Hospital, Gyeongsang National University College of Medicine, 79 Gangnam-ro, Jinju 52727, Korea / Tel: +82-55-750-8839 / Fax: +82-55-750-1709 / E-mail: miranda75@naver.com
• Received: September 6, 2023 • Revised: October 6, 2023 • Accepted: October 11, 2023
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Task-specific tremor (TST) refers to a kinetic tremor that occurs during a specific task often performed repetitively and frequently [1]. Primary writing tremor is most common, and other forms of TST have been identified in musicians and atheletes.2 In this report, we present a case of task-specific hand tremor that exclusively occurred while driving.
A 73-year-old right-handed man who had been driving for 30 years complained of a tremor occurring while driving. His symptoms started one year earlier. Merely holding the steering wheel did not provoke any symptoms, but when symptoms did occur, neither adjusting the seatback angle nor wearing wrist guards alleviated them. The tremor did not affect his driving or any other daily activities, such as writing or using chopsticks.
Neurological examination revealed no remarkable postural tremor or kinetic tremor while drawing an Archimedean spiral, buttoning a shirt, or pouring water. There were no signs of dystonia, including abnormal postures, sensory trick, or overflow. Parkinsonism characterized by bradykinesia, rigidity, or resting tremor was unremarkable, and the patient denied any symptoms of rapid eye movement sleep behavior disorder, hyposmia, or autonomic dysfunction. The patient was asked to bend his arms slightly while holding a round-shaped plastic ring to simulate driving, which did not elicit any tremor, nor did the patient complain of it. When one of the authors accompanied the patient in his car, a small and fast oscillation appeared on the patient’s left hand a few minutes after he started driving, and it disappeared as the car stopped (Supplementary Video 1 in the online-only Data Supplement, Segment 1).
The symptoms persisted without changes, and no medication was administered per the patient’s request. Approximately three years after the symptoms started, the patient was prescribed pregabalin 75 mg twice a day at another hospital for a tingling sensation in both hands. A few days after taking pregabalin, the patient noticed that the tremor had disappeared (Supplementary Video 1 in the online-only Data Supplement, Segment 2).
The patient, a former public servant, had a medical history of atrial fibrillation, diabetes mellitus, and dyslipidemia, which had been well controlled by edoxaban, bisoprolol, metformin, and rosuvastatin. There was no family history of essential tremors or Parkinson’s disease (PD). His biannual health screenings, including thyroid function tests and HbA1c, were all within normal ranges, except for osteopenia. His brain imaging, including 18F-N- (3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane (18F-FP-CIT) positron emission tomography (PET), showed no abnormalities (Figure 1). His nerve conduction study was unremarkable.
The patient presented a left dominant tremor that occurred exclusively while driving, and the symptom persisted for more than three years without evolving into other etiologies. The tremor disappeared after taking pregabalin, which was prescribed for unrelated symptoms.
The current patient’s tremor shares characteristics with TST, as it is only noticeable while driving [2]. The asymmetric manifestation could be compatible with TST [2]. Although TST is frequently observed when performing a skilled task and driving does not require specific expertise, the possibility of TST does not diminish as primary writing tremor, which is the most common subtype of TST, does not necessarily occur in professional writers.
Task-specific dystonic tremor is one of the primary differential diagnoses. However, the patient’s phenotype was compatible with sinusoidal oscillations, and no characteristic features of dystonia were observed either in the neurological examination or while driving. Furthermore, a broad definition of task-specific dystonia includes loss of motor control confined to a specific motor skill [3,4]. However, this patient’s tremor did not affect his driving, making task-specific dystonia less likely.
Pregabalin is a gamma-aminobutyric acid (GABA) analog that binds to voltage-gated calcium channels and blocks calcium influx, resulting in a decrease in the release of excitatory neurotransmitters [5]. Given that disturbance in the GABAergic system, especially in the cerebellum, contributes to essential tremor (ET), the patient’s tremor may be associated with ET. However, the patient’s symptoms do not fit the category of ET, which, according to the current diagnostic criteria, requires bilateral upperlimb action tremor [1].
A previous study reported a few cases of TST in which the patients ultimately developed PD after variable time intervals (2–35 years). Those patients later presented resting tremors on the ipsilateral side of the TST, and dopamine transporter imaging showed a significantly decreased uptake on the contralateral side of the TST. Furthermore, some patients responded well to dopaminergic medication such as levodopa or apomorphine or even to deep brain stimulation, suggesting a connection between TST and PD [6]. However, the patient in our study has shown no parkinsonism to date, and his 18F-FP-CIT PET was negative.
Other possible diagnoses, such as neuropathic tremor, which usually involves bilateral distal upper extremities with frequencies of 3–6 Hz in patients with polyneuropathy; position-specific tremor; or functional movement disorders, were dismissed from clinical assessment and laboratory findings.
The most critical limitation of this report is that electrophysiological studies were not performed. Electrophysiological studies such as somatosensory temporal discrimination threshold or temporal discrimination movement thresholds would have helped reveal the underlying pathophysiology of the current patient’s tremor. The use of wearable sensors equipped with accelerometry, gyroscopes, and electromyography would also have offered more comprehensive analyses of the symptoms. Furthermore, although the 18F-FP-CIT PET early phase image of the patient demonstrated normal regional cerebral perfusion, other imaging modalities, such as functional magnetic resonance imaging or fluorodeoxyglucose imaging, could be utilized to further investigate pathophysiology [7]. Last, the effect of pregabalin should be interpreted with caution. As the patient refused to hold pregabalin to see if the tremor recurred after discontinuation of the medication, it cannot be fully clarified whether pregabalin ameliorated tremor or was by coincidence.
To date, only a few cases with task-specific movement disorders related to driving have been reported (Supplementary Table 1 in the online-only Data Supplement). To the best of our knowledge, task specificity exclusively associated with moving the steering wheel has rarely been reported. This patient’s tremor closely resembled TST and may represent a new subtype within this category. Although the symptoms disappeared after taking pregabalin, continuous monitoring is warranted to see if the patient develops other etiologies.
A Tremor occurred while driving. Segment 1: The patient presented
a tremor while driving, which soon disappeared as the car stopped.
Segment 2: A few days after pregabalin started, the tremor disappeared.
Supplementary Table 1.
Previous reports of task-specific movement disorders related with driving
All procedures performed in this study involving human participants followed the ethical standards of the Institutional Review Board of the Gyeongsang National University Hospital (No. 2022-05-017) and the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. A waiver of informed consent was granted by the Institutional Review Board of the Gyeongsang National University Hospital (No. 2022-05-017), Korea.
Conflicts of Interest
The authors have no financial conflicts of interest.
Funding Statement
This research was supported by the National Research Foundation (NRF) funded by the Korean government (Ministry of Science and ICT) (No. 2020 M3E5D9080663 and No.NRF-2021R1F1A1050970).
Author contributions
Conceptualization: Minkyeong Kim, Heeyoung Kang. Data curation: Minkyeong Kim, Eunji Kim, Seok Min Moon, Juhyeon Kim. Funding acquisition: Minkyeong Kim, Heeyoung Kang. Methodology: Minkyeong Kim, Juhyeon Kim, Heeyoung Kang. Project administration: Minkyeong Kim. Supervision: Minkyeong Kim, Juhyeon Kim, Heeyoung Kang. Visualization: Minkyeong Kim, Eunji Kim, Seok Min Moon. Writing—original draft: Minkyeong Kim, Eunji Kim, Seok Min Moon, Juhyeon Kim. Writing—review & editing: Minkyeong Kim, Juhyeon Kim, Heeyoung Kang.
Figure 1.
18F-FP-CIT positron emission tomography findings of the patient. 18F-FP-CIT positron emission tomography showed normal striatal dopamine transporter binding. The early phase is presented on the left, and the delayed phase is presented on the right. 18F-FPCIT, 18F-N-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane.
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