Smiling corresponds to the psychomotor function in Parkinson’s disease

Abstract

The facial expression is a primary communication tool in human social life at all ages and in all countries. At a medical office, a physician can judge physical and/or mental problems from the facial expression of a patient in the consulting room. A physician considers a patient to be well when he or she seems to be happy. However, there is no method of evaluating the facial expression of patients. Parkinson’s disease (PD) is a progressive neurodegenerative disorder, characterized by tremor, rigidity, bradykinesia, and numerous non-motor symptoms, including cognitive and mood disturbances [1, 2]. PD patients show a characteristic countenance, the ‘‘masked’’ or ‘‘poker’’ face, which is presumed to be caused by bradykinesia of the facial muscles as well as psychological problems. However, the patients sometimes smile when they are feeling well. We tried to determine whether the degree of smile was associated with the psychomotor symptoms in PD using a real time smile detector, SmileScan (OMRON, Tokyo, Japan). We prepared five questions. The 20-s mean smile ratio (0–100 %) was measured, while a patient in on state was asked the questions. The smile ratio was measured once again on another day, and the average of the two smile ratios was obtained. PD patients (n = 62; age, 70.59 ± 1.88 (mean ± SE), Hoehn & Yahr stage, 3.06 ± 0.032) showed a lower mean smile ratio (16.95 ± 2.33 %, p = 0.029) compared with age-matched controls (24.85 ± 2.71 %) (n = 74; age 67.2 ± 1.78). We then determined whether the smile ratio was correlated with motor disability and/or depression scores in PD patients. Figure 1 shows that the smile ratio was negatively correlated to the Unified Parkinson Disease Rating Scale (UPDRS) motor score (p = 0.041) and the Self-rating Depression Scale (SDS) (p = 0.0023). An earlier study of facial expression in PD using a videotape/microcomputer-based method suggested a reduced frequency of smiling [3]. Recent progress in computer-based facial recognition systems has enabled us to easily identify and quantify facial expression. In particular, smile analysis technology, as used in SmileScan, which recognizes people’s smiles in pictures from a digital camera and automatically measures them in real time, has been developed in Japan. The present results indicate that the smile is associated with a psychomotor function of PD and the smile ratio may be a useful index of this function. Mental stress is known to be associated with an exacerbation of parkinsonism. Our results are concordant with the clinical observation that PD patients tend to smile when their symptoms are well controlled. Several studies have demonstrated that PD patients are highly sensitive to the placebo effect [4, 5]. The growing understanding of the placebo effect indicates that psychological mechanisms such as expectation and conditioning might induce a druglike effect by activating dopamine release and modulating neuronal excitability in the brains of PD patients [4, 5]. Considering the significant correlation between the smile ratio and the psychomotor function, we are interested in discovering whether smile training would be effective in treating PD patients. Possibly, the following proverb might be true for PD, ‘‘Smile, and you will win’’. K. Kawamura (&) Y. Arii T. Mitsui Department of Neurology, Tokushima National Hospital, National Hospital Organization, 1354 Shikiji, Kamojima, Yoshinogawa 776-8585, Japan e-mail: kawamura@tokusima.hosp.go.jp