The Prevalence and Clinical Characteristics of Essential Tremor in Elderly Chineses: A Population-Based Study

Abstract

Objectives

To investigate the prevalence and the clinical feature of essential tremor (ET) in a community cohort in Beijing.

Methods

Using a door-to-door, two-phase approach, we investigated 2,835 residents aged ≥55 years old from rural, urban, and mountain areas.

Results

The prevalence rate of ET was 4.29%, 2.85%, and 2.29% in rural, urban, and mountain areas, respectively. The overall age- and sex-adjusted prevalence was 3.29%. Among those aged ≥75 years, the prevalence rate in the urban area was higher than those in the rural and mountain areas. The prevalence rate increased with age, and the prevalence was higher among men (6.0%) than among women (3.6%). There was a correlation of ET prevalence with age, sex, and habitation area, but not with alcohol, tea drinking, and occupation. Women (25%) with ET were more likely to have head tremor than men (16.9%).

Conclusions

The ET prevalence in the elderly of Beijing was 3.29% which is higher in the urban area and in men.

Introduction

Essential tremor (ET) is considered the most prevalent adult movement disorder and is regarded as one of the most common adult neurological disorders (1, 2). Despite the frequently used qualifying term “benign,” ET may cause substantial physical and psycho-social disabilities (3). However, information about its prevalence and distribution is limited because of the difficulty in diagnosing patients with ET in the population.

Several epidemiological studies have been service-based (clinic or record based) and have used hospital records; this method generates data that are not representative. The generally accepted gold standard in an epidemiological study is one that is community-based, wherein subjects from a defined geographical area are identified using personal interviews and examinations (4, 5). The estimates of the crude prevalence of ET across the few worldwide community-based surveys vary specifically, with a prevalence of ET in the elderly population-based surveys ranging from 3.9%–22% (6, 7, 8, 9). This study aimed to investigate the prevalence of physician-diagnosed ET from the three representative communities in Beijing, China. The clinical characteristics and its regional differences were also explored.

Subjects and methods

Cohort description

The study was carried out at the follow up stage of the Beijing Longitudinal Study on Aging (BLSA) in 2000(10). The BLSA cohort was established in 1992 and followed up every 2–3 years since then. A multi-step stratified random sampling method was used to select a cohort whose geographic distribution, age, economic, and education levels were similar to the population from Beijing. Three districts of Xuanwu, Daxing, and Huairou were randomly selected. Xuanwu is a central urban area, Daxing is a rural area, and Huairou is a mountainous area. The baseline population was 3,257 in 1992. In order to maintain a stable size of the cohort, 1,022 subjects randomly selected from the same districts were added in 1994 while another 500 younger subjects between 55 and 60 years old were joined in 2000. All the population was selected with the same principle as 1992. As shown in Figure 1, 2,835 subjects were interviewed for ET, parkinsonism, and dementia in 2000.

Figure 1.

Flow of patients with ET through the study, a. First phase: screening as suspected ET parkinsonism or cognitive disorder; b. Second phase for final diagnosis made by two neurologists individually

Door-to-door, two-phase approach

First phase-initial screening

In the initial screening phase, interviewers who were trained to ask questions in a uniform manner visited the participants at their homes or at nearby clinics for face-to-face interviews. The interview included questions on demographic characteristics, health status, medications, exposures, and lifestyle. Tremor observations were also conducted by the interviewers, wherein the postural and resting tremor was visually examined. People diagnosed with ET previously by doctors or self-reported a history of tremor or detected positive for tremor by the interviewers were further followed up with neurological examination.

Second phase-clinical diagnosis

Subjects who were identified as being positive for tremor and cognitive disorder during the initial screening phase underwent a neurological evaluation by neurologists. Detailed examination for tremor and differential diagnosis for ET were performed. The diagnosis of ET concordance with the criteria of the Essential Tremor Consortium, NIH in 1996 (11). During the neurological examination, only people with a visible tremor were further rated using the tremor rating scale. Tremor was scored separately for different parts of the body as well as different tremor types, such as resting, postural, and kinetic tremor (0–4 scales, total score is 80). Tremor assessment also included rating of the tremors while drawing spirals and tremors during handwriting. Functional performance test included pouring water from one cup to another. Medical records of these participants were also reviewed whenever possible. The final diagnosis was made by two neurologists individually. If a consensus was not reached, a third senior neurologist was asked to give his/her neurological evaluation to establish the final diagnosis.

Table 1.

Age and gender specific crude prevalence of definite ET

Age	Male			Female			Total
	N	Case	%	N	Case	%	N	Case	%
55–64	258	7	2.7	269	2	0.7	527	9	1.7
65–74	590	31	5.3	643	14	2.2	1233	45	3.7
≥75	534	45	8.4	541	36	6.7	1075	81	7.4
Total	1382	83	6.0	1453	52	3.6	2835	135	4.8

Data Analyses

The prevalence of ET was calculated and stratified as per sex and age (55–64 years, 65–74 years, and ≥75 years). Ninety-five percent confidence intervals for each prevalence estimate were derived using exact methods for a binomial parameter. The prevalence estimates were adjusted by age and sex for the population aged ≥55 years in Beijing to estimate the overall prevalence rates in the district. Statistical analyses were performed using SPSS version 11.0.

Results

Of the 2,835 subjects, 1,069 (37.7%) were screened positive in the initial phase for tremor and 1,060 (99.2%) consented to undergo a neurological examination in the clinical diagnosis phase. Of the 1,060 subjects, 354 (33.4%) were observed to have tremor by neurologists and subjected to further consensus diagnosis and assessment using tremor rating scales. Total 135 subjects (52 women and 83 men) fulfilled the diagnostic criteria for definite ET and 120 as probable and possible ET. We found 20 subjects with PD and 9 with parkinsonism. Seventy subjects were diagnosed with physiological tremor or other diseases (Figure 1).

As shown in Table 2, the crude prevalence of definite ET was 4.8 per 100 persons, and the age-adjusted prevalence of definite ET in Beijing was 3.96%. Men had significantly higher prevalence than women in our study (6% vs. 3.6%, x2= 9.199 p = 0.002). The rate of definite ET increased with age in both sexes. Urban areas had slightly higher rate of definite ET than mountainous and rural areas (x2 = 8.673, p =0.013) (Table 2). Similar trends of increased rates of definite ET with age were observed in both urban and mountain areas but not in rural areas.

Table 2.

Residence and age specific prevalence of definite ET

Age	Mountain area			Rural area			Urban area
	N	Case	%	N	Case	%	N	Case	%
55–64	115	1	0.9	84	2	2.4	328	6	1.8
65–74	229	8	2.7	332	11	3.3	602	26	4.3
≥75	240	16	6.7	229	8	3.5	606	57	9.4
Total	654	25	3.8(2.3Δ)	645	21	3.3(2.9Δ)	1536	89	5.8(4.3Δ)*

Δ Age- and sex-adjusted prevalence; *urban area had slightly higher rate of definite ET as compared to mountain and rural areas, p < 0.05

Among the definite ET patients, 94 subjects (69.9%) were self-reported tremor, and 90.4% developed tremor before they turned 50 years old. With respect to the location of tremor of definite ET, 100% patients had arm tremor, 12.6% had head tremor, 2.2% had trunk tremor, and 1.5% had voice tremor. The severity of tremor was not different between women and men, irrespective of the total tremor scores (7.2 ± 3.4 vs. 6.5 ± 2.5, p = 0.150), or limb tremor scores (6.0 ± 2.2 vs. 6.3 ± 2.4, p = 0.421). However, women (25%) were slightly more likely to have head tremor than men (16.9%) (Χ2 = 1.322 p =0.250). The limb tremor scores were not different between patients with and without head tremor (6.6 ± 4.1 vs. 6.0 ± 1.6, p = 0.506).

17 definite ET patients (12.6%) had resting tremor. Table 3 presents a further comparison of the clinical differences between ET patients who did and did not have resting tremor. It appeared that ET patients without resting tremor were more likely to manifest head tremor and had lower total and limb tremor scores. There were no significant differences in the age, sex, and disease duration in these patients.

Table 3.

Clinical characteristics of ET with or without resting tremor

Variables	Resting tremor group	Without resting tremor group	p-value
Number	17	118
Mean age	74.5±4.8	76.0±8.3	p=0.294
Gender			p=0.439
Male	9	74
Female	8	44
Self-report	13	81	p=0.512
Disease duration, years (mean ± SD)	11.5±12.8	10.2±10.3	p=0.675
Head tremor	7	20	p=0.020*
Total tremor score (mean ± SD)	10.0±5.7	6.3±1.8	p=0.017*
Limb tremor score (mean ± SD)	8.4±3.9	5.80±1.73	p=0.015*
Posture tremor (mean ± SD)	2.41±1.18	1.99±0.89	p=0.084
Kinetic tremor (mean ± SD)	3.35±1.00	3.69±1.06	p=0.224

*compared with the two groups, p < 0.05; Head tremor: Resting tremor vs without resting tremor, p = 0.020; Limb tremor score: Resting tremor vs without resting tremor, p = 0.015

Discussion

In this study, we found that the population of Beijing has an age-adjusted prevalence of 3.6 per 100 persons for ET. The rate of definite ET increases with age, as consistently seen in previous epidemiological studies (2, 4, 12, 13). The frequency of ET in this study is similar to that in other ethnic population (14, 15, 16). However, regional differences have also been reported that may be related to differences in the methods of case ascertainment, diagnostic criteria, and potentially, the ethnic background (Table 4). Another investigation on the population of rural area was conducted in Shanghai in 2014 (24). There was a great difference between us because of the different diagnosis criteria, screening method and population. Different life style and climate might also account for this inconsistency between the north and south population of China (25).

Table 4.

Community based epidemiology survey of ET

Research	Time	Country	Age (y)	Diagnostic criteria	Prevalence (%)
Benito-Leon et al (14)	1994	Spain	≥65	Action tremor	4.8
Laesson Sjogren, et al (17)	1960	Sweden	All ages	Postural tremor, enhanced by action	1.7
Rautakorpi, et al (18)	1982	Finnish	>40	Postural or action tremor	5.5
Haerer, et al (19)	1982	USA	>40	Action tremor	0.4
Moghal, et al (20)	1994	Canada	≥65	Postural or action tremor	14.0
Lieberman, et al (21)	1994	USA	≥65	Not mention	22.0
Louis, et al (15)	1995	USA	≥65	Postural or action tremor	4.02
Bergareche, et al (22)	2001	Spain	≥65	Action tremor	4.8
Louis CS.Tan. et al (23)	2001	Singapore	≥50	Postural or action tremor, 3 years history, family history, alcohol effective	0.237
Hiasen, E.H. et al (13)	2016	USA	≥40	Postural or action tremor	3.1
Eung Seok Oh. et al (16)	2005	Korea	≥65	Bilateral postural or action tremor	3.64
Wu, et al.et al (24)	2011	China, Shanghai	≥50	Bilateral postural tremor with or without kinetic tremor, 5 years history	0.306

It was noteworthy that in our study, men were 1.7 times more likely to develop ET than women, like some of the previous studies. However, some studies have suggested opposite results, while others found no sex-based differences (22, 26, 27). The higher rate of ET in men might suggest that male sex (and the related behavior) or environmental factors may play role in the development of ET (23). In addition, we found that women with ET were more likely to have head tremor than men, as demonstrated in another study (28). Whether hormonal factors are involved in the expression of head tremor is unclear.

There was a regional difference in the distribution of ET among the urban, mountain, and rural areas in Beijing. The prevalence of definite ET was higher in urban areas than in the mountain and rural areas, particularly among older subjects (age ≥75, p =0.013). Other studies have not reported similar findings. The higher prevalence in the urban area might be attributable to considerable exposure to environmental risk factors, such as air pollution and pesticides or herbicides. Although specific environmental risk factors for ET have not been identified, exposure to lead (29), pesticides (30), and other toxins is reported to result in action tremor. In addition, people living in mountainous and rural areas are more likely to perform physical labor and exercise daily, protecting them against ET. Our results warrant further investigation on the relationship of environmental and physical factors with ET.

Among subjects with definite ET, 94 (69.6%) themselves reported that they had tremor, while 41 (30.4%) were unaware of any tremor and were diagnosed by interviewers; the diagnosis was confirmed with neurological examination. Head tremor was 3.5 times higher in self-reported subjects (25.5%) than those who were unaware about it, suggesting that head tremor was the main factor affecting the awareness regarding tremor. Most community-living subjects with tremor were only affected mildly and usually did not seek medical attention.

Resting tremor is usually the manifestation of PD; however, ET patients may have both postural and resting tremor (31). To better investigate the relationship of resting tremor with ET, we compared the differences in the clinical features of ET patients with and without resting tremor. The major differences were more head tremor and less severity of tremor in ET patients without resting tremor. Our data support the fact that a small proportion of definite ET patients could have mixed tremor. Recently, the term “Essential Tremor Plus” was proposed by Louis ED (32). ET with tremor at rest is included in this category. Further investigation is necessary in such cases.

There are certain limitations of this study. People aged <55 years were excluded. Videotaped evidence was only available for few cases though the diagnosis was made onsite by neurologists. Since the baseline study of the cohort began in 1992, 8 years ago before our diagnosis, and almost one third of the initial subjects died. We would not know if there were any factors that may selectively affect our results, particularly for the different rate between genders and residence.

Conclusions

The current study found a similar prevalence and increased rate with age of definite ET in the Beijing community as compared to that in other countries. Further research is warranted to understand whether environmental factors or sex-related behavior affects the prevalence of ET.

Ethical Standards

All participants were asked to sign an informed consent form and the project was approved by ethic committees of Xuanwu Hospital of Capital Medical University. Written informed consents were obtained for every subject.

Conflicts of interest

Nothing to report.