Smiling Tremor in a Patient with Essential Tremor

A 60-year-old man with a history of diabetes attended the movement disorders clinic due to facial tremor occurring exclusively when he smiled or laughed. The facial tremor emerged around age 35 and had gradually increased in intensity and frequency over time. He also had mild action and postural tremor in both hands since adolescence, without functional impairment. There was no dysarthria, slowness in movements, gait disturbance or cognitive impairment. The smiling tremor and hand tremor both improved when he consumed a small amount of alcohol, but were refractory to propranolol or topiramate. He had no exposure to any medications known to cause tremors. MRI of the brain was unremarkable. Family history was significant for essential tremor (ET) in his mother. On examination, he had jerky trembling in both cheeks when smiling (“small” or “big” smile, Video 1) or clenching his teeth. Neurological examination was normal. Electrophysiological evaluation revealed a synchronous tremor (7.5 Hz) in the facial muscles (Fig. 1(A) and S1). The tremor persisted but decreased in amplitude during teeth clenching, and was absent while the patient was speaking, forcefully smiling (Fig. 1(B), Video 1), protruding the tongue or puffing his cheeks. The facial tremor was unaffected by finger tapping or by placement of a tuning fork on the forehead (lack of distractability or entrainment). Needle electromyogram revealed no evidence of myokymia. Additionally, both arms had a 6-Hz alternating tremor when positioned in a batwing posture, holding a mug or drawing a spiral (Video 1). The tremor was intermittent with the arms outstretched and showed no frequency modulation with weight loading, consistent with ET (Fig. 1(C),(D)). Smiling tremor has been proposed to be dystonic temor,1 based on its absence during maximal facial contraction as observed in our patient—analogous to the “null point.” However, the lack of dystonia argues against this interpretation. The absence of smiling tremor with full effort suggests that it is not an isometric tremor. The perioral muscles lack muscle spindles required for the mechanical mechanism of enhanced physiologic tremor.1 The clinical symptoms and signs do not support a parkinsonian tremor. In our patient, the action-specific nature, co-occurrence with upper limb tremor, and alcohol-responsiveness suggest that the smiling tremor may be a manifestation of ET. Since its first description in 1987, there have been a total of eight cases of smiling tremor reported,1 and none had tremor beyond the face. Facial muscles are rarely affected in ET, and when they are, the tremor is not specific to smiling.2 In 2018, the Task Force on Tremor of the International Parkinson and Movement Disorder Society classified task-specific tremor as a separate entity from ET and ET-plus.3 However, some patients with a diagnosis of pure ET based on the 2018 consensus may experience task-specificity at onset,4 and a forehead task-specific tremor occurring exclusively while speaking has been reported in one patient with ET.5 The coexistence of ET and smiling tremor, which is task-specific but lacks prominent dystonic features, in our patient suggests that ET spectrum may include the phenomenology of task-specific tremors. (1) Research project: A. Conception, B. Execution; (2) Analysis: A. Design, B. Execution, C. Review and critique; (3) Manuscript: A. Writing of the first draft, B. Review and critique. J.C.C.: 2A, 2B, 3A. T.G.: 1A, 1B, 2A, 2C, 3B. Y.M.: 2C, 3B. G.K.: 3B. R.C.: 1A, 2C, 3B. We thank the patient for allowing publication for educational purposes. Ethical Compliance Statement: We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. The authors confirm that the study was approved by the University Health Network Research Ethics Board (reference number 24–5646), and that written consent was obtained from the patients. Funding Sources and Conflicts of Interest: No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work. Financial Disclosure for the Preceding 12 Months: The authors declare that there are no additional disclosures to report. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Figure S1. Electrophysiological recording for big smile. (A) Surface electromyogram revealed synchronous tremors in facial muscles with a mean frequency of 7–8 Hz. (B) The spectra of the rectified EMG and accelerometer signal demonstrated a peak at approximately 7.5 Hz. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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