Essential tremor (ET) is one of the most prevalent neurological diseases; its hallmark feature is action tremor,1–4 although other motor features may be present (i.e., intention tremor or mild ataxia).5–8 The disease is associated with functional disability9 and diminished quality of life.10 ET is chronic and progressive, and patients often feel a worsening of symptoms over time even when their tremor remains stable.11 In addition to motor features, patients may experience a range of non-motor features, including anxiety, social phobia, depression, and sleep dysregulation.12–14 Moreover, a significant portion of ET patients (30–60%) have cognitive deficits, which range from subclinical abnormalities to mild cognitive impairment (MCI) and dementia.10,15,16 Although the motor and non-motor features of ET have been characterized in some detail, it is not known whether ET patients are suffering psychologically and whether those who are close to them (i.e., “close others” [COs], their family members and friends) consider them to be suffering in this way. It is also unknown whether the perception of patient psychological suffering is associated with depression in those who are close to them. Here, we draw from Schulz et al.’s17 conceptualization and validated measure of psychological suffering to understand these interpersonal processes. Schulz and colleagues define psychological suffering as the frequent experience of negative emotions and thoughts, such as worry, hopelessness, anger, loneliness, and guilt, in the context of a physical illness.17 In addition, Schulz and colleagues suggest that informants be asked with a single item to rate the patient’s suffering on a scale from 1 to 10, where suffering is defined by the informants themselves.
Research on family caregiving shows that family members’ perceptions of patient suffering predict family members’ poor psychological and physical health. Moreover, this is independent of the physical demands of providing care and the level of the patient’s disability or disease severity.18 Past research also shows that family members tend to overestimate patients’ suffering, which may create problems with communication between patients, family members, and other caretakers, as well as clinicians.19 Little to nothing is known about these interpersonal processes in ET.
This is the first paper to describe and quantify ET patients’ experiences of psychological suffering and the correlates of that suffering. Additionally, we quantify the perceptions of COs of psychological suffering beyond physical disability associated with having ET. Furthermore, in the present paper we tested the following specific hypotheses. First, we hypothesized that the perceptions of COs of patient psychological suffering would be higher than patients’ self-reports (Hypothesis 1). Second, we hypothesized that greater patient psychological suffering would be associated with greater patient depressive symptoms (Hypothesis 2a), and COs’ greater perceptions of patient psychological suffering would be associated with greater depressive symptoms in the COs (Hypothesis 2b). Finally, we hypothesized that the greater perceptions of COs of patient psychological suffering would be associated with greater daily stress for COs (Hypothesis 3). To examine whether the association between psychological suffering and depression was independent of tremor characteristics (i.e., tremor duration, disability, and severity), we entered these tremor characteristics as covariates in our statistical models. We also conducted a sensitivity analysis to account for potential influences of cognitive impairment and comorbidity on our main associations.
ET patients were recruited through the Clinical Pathological Study of Cognitive Impairment in Essential Tremor (COGNET; NIH R01 NS086736), which is an ongoing, nationwide, longitudinal study that evaluates cognitive function in older persons with ET (mean age at baseline=79.2±9.5 years). The study began in July 2014 and recruitment was achieved through advertisements on patient advocacy group websites using the following eligibility criteria: 1) diagnosis of ET, 2) age ≥ 55 years, 3) no history of surgical interventions for ET, and 4) willingness to be a brain donor and perform study measures. As part of the COGNET protocol, the cohort of ET patients underwent a 4–6-hour evaluation conducted by trained research assistants (S.K., S.M., K.C., or B.R.) in patients’ homes throughout the United States. This assessment included motor, neuropsychiatric, and neuropsychological measures at baseline. Based on this assessment, cognitive diagnoses (normal cognition, MCI, or dementia) were assigned to each ET patient through a consensus conference as described in detail.20 Regular follow-up evaluations were performed at 18-month intervals, using the same measures, to ensure the presence of updated clinical and cognitive data on this cohort of brain donors.
The current analyses, which used data from the baseline assessment, considered the first 50 ET patients and their family members who completed an additional, 30-minute assessment of suffering in ET conducted between October 2015 and July 2016.
For all patients enrolled in this study, ET diagnoses were carefully assigned. First, patients were diagnosed with ET by their local physician (neurologist, internist, or general practitioner). Second, as part of their 4–6-hour evaluation, patients completed a series of structured clinical questionnaires and underwent a standardized, videotaped neurological examination, which included a detailed assessment of postural tremor (two positions), kinetic tremor (five tests), intention tremor of the arms and head, and the motor portion of the Unified Parkinson’s Disease Rating Scale21 except for rigidity. The severity of postural and kinetic tremors was rated (ratings=0–3) on 12 items by a senior movement disorders neurologist (E.D.L.), resulting in a total tremor score (range 0–36),22 which is a reliable23 and valid24 measure of the severity of the action tremor. Then, published diagnostic criteria (moderate or greater amplitude kinetic tremor [tremor rating ≥ 2] during three or more videotaped activities or a head tremor in the absence of Parkinson’s disease or other known causes)23–25 were applied.
COs recruited for this study were identified directly by each patient as “someone who knows you well and sees you often” and who can “provide a different perspective on your well-being.” Most of these individuals were family members (88%) and a significant majority (62%) lived with the patients. On average, they provided 5.4 hours of care per week.26 Data on the demographics of COs, and experiences and perspectives on suffering, were collected during 30-minute telephone interviews conducted by trained research assistants (S.K., S.M., K.C., B.R., or F.M.) between October 2015 and July 2016.26
Upon enrollment, all ET patients provided informed written consent approved by the Institutional Review Boards of Columbia and Yale Universities. All COs enrolled in the study provided verbal consent over the telephone approved by the Institutional Review Board of Yale University.
As part of their 4–6-hour evaluation, each patient was visited at home by a trained research assistant (S.K., S.M., K.C., or B.R.) who conducted a detailed clinical and cognitive assessment and obtained a videotaped neurological examination as described above. This in-person assessment also included the following measures.
Using a reliable and valid scale from 0 (not at all) to 3 (very often/every day), patients were asked to rate the extent to which they experienced 15 psychological symptoms (e.g., afraid, worried or anxious, a burden to others) during the past 7 days.17 The present study added three items that ET patients frequently raise during clinical visits (frustrated, focus of unwanted attention, and feeling infirm) to make a modified scale. Scores for the modified scale can range from 0 to 48, with higher scores indicating greater psychological suffering. The score for the unmodified scale can range from 0 to 39. Patients were additionally asked to rate their overall suffering during the past week from 0 (did not suffer at all) to 10 (suffered a great deal).17
We used the Geriatric Depression Scale (GDS), a self-report measure of 30 questions about the presence of depressive symptoms such as helplessness, hopelessness, and lack of energy.27 Scores can range from 0 to 30 with higher scores indicating greater depressive symptoms.
To assess self-reported disability due to tremor, we used a valid and reliable28,29 disability questionnaire for ET.28 This questionnaire asked patients to report their difficulty in completing (0=no difficulty, 1=need to modify action, 2=disability) a range of daily activities (e.g., carrying a cup, tying shoe laces, signing name, etc.). The tremor disability score ranged from 0 to 20 with higher scores denoting greater impairment.
Each patient also had a clinical diagnosis of cognitive status based on a clinical case conference. The status options were normal cognition, MCI, dementia.
Patients self-reported the total number of medications taken; this was used as a surrogate marker for medical comorbidity.
Each CO was contacted by a trained research assistant (S.K., S.M., K.C., B.R., or F.M.) to conduct a semi-structured interview over the telephone. The telephone interviews were conducted between 1 week and 3 months after the in-person assessment of ET cases. COs provided demographic, socioeconomic, and caregiving information. They also completed the following assessments.
COs were asked to rate how often they perceived that the patient was suffering using the same psychological suffering scale and the overall suffering item.
COs were asked to complete the Center for Epidemiological Studies Depression Scale (CESD-10; range 0–30).30 This is a reliable and valid31 self-report instrument consisting of 10 items that evaluate the frequency of experiencing symptoms such as feeling depressed, feeling fearful, and feeling lonely. Higher scores indicated greater severity of depressive symptoms. The CESD-10 was used to assess COs’ depressive symptoms instead of the GDS because many COs were not older adults, making the GDS less appropriate for a diverse sample of ages.
COs were asked to rate their average daily stress level with a single item that ranged from 1 (not at all stressed) to 10 (extremely stressed). We used a single item to minimize participant burden and because single item stress measures have been found to be valid and reliable.32
Statistical analyses were performed in SPSS (version 21.0; Chicago, IL, USA). To describe the extent of self-reported and perceived psychological patient suffering, means and standard deviations are presented. To compare our data with prior studies, we also report the means and standard deviations for the unmodified psychological suffering scale; however, we used the modified psychological suffering scales in all hypothesis-testing analyses. Because the main variables were not normally distributed, we used non-parametric tests (i.e., Wilcoxon Signed Ranks tests, Spearman’s rank correlations and the Mann–Whitney tests).
To assess the relationship between self-reported and perceived suffering (independent variables) and depressive symptoms (dependent variable), we used logistic regression models. For this purpose, we divided cases and COs into two categories based on GDS and CESD-10 scores, respectively. ET patients with a GDS score ≥10 were categorized, according to established guidelines, as having moderate to severe depressive symptoms.27 COs with a CESD-10 score ≥8 were categorized as having moderate to severe depressive symptoms.30,33
To maintain parsimony in the models predicting depression, we entered only the patient self-reported suffering variables when predicting patient self-reported depression. Likewise, to test associations for COs, we entered only the perceived suffering variables of COs predicting the self-reported depression of COs. Research on close relationships shows that one’s own perceptions of partner behaviors and feelings tend to be more predictive of one’s own well-being than partner self-reports of their behaviors and feelings.34 Next, linear regression models assessed the relationship between perceived psychological and overall suffering (independent variables) and COs’ daily stress level (dependent variable). For all models, we controlled for tremor duration, tremor disability score, and total tremor score. Next, to explore the influence of cognitive status of ET patients, we conducted a sensitivity analysis by excluding the dyads of ET patients with cognitive deficits (mild cognitive impairment and dementia) and re-ran all correlations. Finally, to account for ET patients’ comorbidity, we examined correlations between ET patients’ number of medications (i.e., a surrogate marker for medical comorbidity) and the suffering, depression, and stress variables. We also conducted sensitivity analysis, including number of medications as a covariate in all analyses testing the main hypotheses.
Dyads consisted of 50 pairs of ET patients and COs who completed all required questionnaires for the current analysis. The mean age of ET patients was 76.8±10.6 years and the mean age of tremor onset was 42.1±22.1 years (Table 1). The mean age for COs was 65.4±12.5 years. The majority of patients and COs were female (62% and 66%, respectively) (Table 1). Based on cognitive testing, 41 (82%) ET patients had normal cognition, seven (14%) had MCI, and only two (4%) were diagnosed with dementia. Thirty-one (62%) COs lived with the ET patients and a large majority (88%) were either the spouses or adult children. Of the remaining 19 COs, 14 (73.7%) spent at least 30 days per year seeing the ET patients. On average, COs spent 5.4 hours±10.2 hours per week caring for the ET patients.
|Family history of ET||23||NA|
|Tremor duration (years)||34.7±21.0||NA|
|Age at tremor onset (years)||42.1±22.1||NA|
|Tremor disability score||14.2±4.8||NA|
|Self-reported head tremor||6||NA|
|Total tremor score||20.5±5.6||NA|
|Geriatric depression scale||6.2±5.5||NA|
|Relationship to case||NA|
|Times per year seeing case||NA|
|Lives with case||31|
|Self-reported daily stress level||NA||4.3±2.1|
Table 2 shows the means and ranges of patient and CO reports of modified and unmodified patient psychological and overall suffering. In terms of clinical correlates of psychological and overall suffering, as shown in Table 3, ET patients’ self-reported psychological suffering was positively correlated with tremor duration (r=0.31, p=0.02) and tremor disability score (r=0.36, p=0.01). ET patients’ self-reported overall suffering was significantly correlated with tremor disability score (r=0.36, p=0.01). Additionally, COs’ perceptions of psychological suffering were positively correlated with tremor duration (r=0.28, p=0.04), and perceived overall suffering was similarly correlated with the tremor disability score (r=0.32, p=0.02; Table 3).
|ET Patients’ Self-report of Suffering||COs’ Perception of Suffering|
|Correlation with self-reported psychological suffering
mean±standard deviation (median) of self-reported psychological suffering
|Correlation with self-reported overall suffering
mean±standard deviation (median) of self-reported overall suffering
|Correlation with perceived psychological suffering
mean±standard deviation (median) of perceived psychological suffering
|Correlation with perceived overall suffering
mean±standard deviation (median) of perceived overall suffering
|Age of ET patient (years)||r=0.081||r=0.151||r=0.131||r=−0.081|
|Age of COs (years)||r=−0.071||r=−0.171||r=−0.071||r=−0.071|
|Gender of ET patient|
|Male||11.4±11.9 (6.0)2||3.8±2.9 (3.0)2||11.4±11.9 (6.0)2||3.8±2.9 (3.0)2|
|Female||11.4±7.7 (9.0)||3.1±1.6 (3.0)||11.4±7.7 (9.0)||3.1±1.6 (3.0)|
|Gender of COs|
|Male||7.9±4.1 (7.0)2||3.6±2.3 (7.0)*2||9.3±7.7 (7.0)2||2.9±1.5 (3.0)2|
|Female||8.9±9.0 (7.0)||2.4±1.9 (2.0)||12.5±10.1 (9.0)||3.6±2.5 (3.0)|
|Education of ET patients (years)||r=−0.071||r=−0.171||r=0.101||r=−0.191|
|Education of COs (years)||r=0.061||r=0.30*1||r=0.171||r=0.151|
|Family history of ET|
|Yes||9.5±9.2 (7.0)2||3.3±2.4 (3.0)2||9.5±9.2 (7.0)2||3.3±2.4 (3.0)2|
|No||11.0±9.4 (11.0)||3.5±2.0 (3.0)||11.0±9.4 (11.0)||3.5±2.0 (3.0)|
|Tremor duration (years)||r=0.31**1||r=0.161||r=0.28**1||r=0.201|
|Age at tremor onset (years)||r=−0.24*1||r=−0.101||r=−0.191||r=−0.161|
|Tremor disability score||r=0.36***1||r=0.36**1||r=0.121||r=0.32**1|
|Total tremor score||r=0.081||r=0.161||r=0.121||r=0.25*1|
|Total medications for ET patients||r=0.27||r=0.19||r=0.50***||r=0.44***|
|Psychological suffering score|
|Overall suffering score|
|Geriatric Depression Scale||r=0.76***1||r=0.47***1||r=0.46***1||r=0.45***1|
|CO stress level||r=0.33**1||r=-0.041||r=0.37***1||r=0.27*1|
As hypothesized (Hypothesis 1), COs perceived significantly more psychological suffering and overall suffering than reported by ET patients (Table 2).
Nine (18%) ET cases and 12 (24%) COs were found to have moderate to severe depressive symptoms. In terms of correlations, patients’ depressive symptoms were significantly correlated with self-reported psychological suffering (r=0.76, p<0.001) and overall suffering (r=0.47, p<0.001; Table 3). Depressive symptoms in COs were significantly correlated with COs’ perceptions of psychological suffering (r=0.33, p=0.02), but not COs’ perceptions of overall suffering (r=0.26, p=0.07; Table 3).
Supporting hypotheses 2a and 2b, binary logistic models revealed that greater self-reported psychological suffering was associated with a higher likelihood of ET patients experiencing moderate to severe depressive symptoms (Wald χ2=5.52, degrees of freedom [df]=1, odds ratio [OR]=1.42, 95% confidence interval [CI]=1.06–1.91, p=0.02; Table 4). However, greater self-reported overall suffering was not significantly associated with a higher likelihood of ET patients experiencing moderate to severe depressive symptoms (Wald χ2=1.56, df=1, OR=1.28, 95% CI=0.86–1.90, p=0.21). Greater CO perception of psychological suffering (Wald χ2=8.96, df=1, OR=1.26, 95% CI=1.08–1.47, p<0.001) and overall suffering (Wald χ2=7.89, df=1, OR=2.62, 95% CI=1.34–5.13, p=0.005) were each associated with a higher likelihood of COs experiencing moderate to severe depressive symptoms.
|Wald Statistic (1 df)||Odds Ratio||95% Confidence Interval||p|
|Model 1: ET patient psychological suffering predicting depression|
|Self-reported psychological suffering||5.52*||1.42||(1.06, 1.91)||0.02|
|Tremor duration||0.01||1.00||(0.95, 1.06)||0.93|
|Tremor disability score||3.39||1.41||(0.98, 2.04)||0.07|
|Total tremor score||2.41||0.81||(0.61, 1.06)||0.12|
|Model 2: ET patient overall suffering predicting depression|
|Self-reported overall suffering||1.56||1.28||(0.86,1.90)||0.21|
|Tremor duration||0.36||1.01||(0.97, 1.06)||0.55|
|Tremor disability score||2.92||1.30||(0.96, 1.74)||0.09|
|Total tremor score||0.69||0.91||(0.74, 1.13)||0.41|
|Model 3: CO perceived psychological suffering predicting depression|
|Perceived psychological suffering||8.96**||1.26||(1.08, 1.47)||0.00|
|Tremor duration||0.43||0.96||(0.96, 1.08)||0.51|
|Tremor disability score||0.47||0.69||(0.69, 1.19)||0.49|
|Total tremor score||4.92*||0.49||(0.49, 0.96)||0.03|
|Model 4: CO perceived overall suffering predicting depression|
|Perceived overall suffering||7.89**||2.62||(1.34, 5.13)||0.005|
|Tremor duration||1.16||1.03||(0.98, 1.09)||0.28|
|Tremor disability score||0.92||0.88||(0.68, 1.14)||0.34|
|Total tremor score||6.21*||0.65||(0.46, 0.91)||0.01|
Multiple linear regression models (Table 5) also revealed that COs’ perception of psychological suffering (β=0.34, t(4)=2.87, p=0.01) and overall suffering (β=0.31, t(4)=2.42, p=0.02) were each associated with higher levels of self-reported daily stress, supporting Hypothesis 3.
|B Coefficient||Standard Error||Beta||T||p|
|Model 1: Perceived psychological suffering predicting CO daily stress|
|Perceived psychological suffering||0.08||0.03||0.34||2.87||0.01|
|Tremor disability score||0.04||0.05||0.10||0.82||0.42|
|Total tremor score||–0.02||0.05||–0.05||–0.46||0.65|
|Model 2: Perceived overall suffering predicting CO daily stress|
|Perceived overall suffering||0.30||0.12||0.31||2.42||0.02|
|Tremor disability score||0.02||0.06||0.04||0.31||0.76|
|Total tremor score||–0.03||0.05||–0.07||–0.54||0.59|
When ET patients without MCI or dementia were in the analysis only (n=41), the correlations between suffering, tremor severity variables, and severity of depressive symptoms in both the ET cases and their COs remained largely the same. Patients’ psychological suffering (r=0.75, p<0.001) and overall suffering (r=0.24, p=0.15) were correlated with patient depressive symptoms either significantly or in the same direction. The findings for the depressive symptoms of COs also remained the same as in the main analysis (perceptions of patient psychological suffering, r=0.49, p=0.001; overall suffering, r=0.29, p=0.06). Associations with COs’ daily stress were in the same direction but no longer significant (perceived psychological suffering, r=0.20, p=0.20; overall suffering, r=0.22, p=0.15).
Twenty-four of the 50 ET patients were on five medications or more. The mean number of medications was 5.53±4.06 (range=0–20, SD=4.06). Correlational analysis revealed that COs perceived greater ET psychological and overall suffering when ET patients took more medications; however, ET patients’ self-reported psychological and overall suffering were not significantly related to greater number of medications (Table 3). We re-ran all models that included CO perceived suffering variables as predictors, adding ET patients’ number of medications as a covariate, and the results did not significantly change (CO perceived psychological suffering still predicted depression (β=0.23, Wald=7.77, p=0.01) and daily stress (β=.36, t=2.66, p=0.01); CO perceived overall suffering still predicted depression (β=1.04, Wald=6.78, p=0.01) and daily stress (β=.39, t=2.90, p=0.01).
To understand how much suffering patients were self-reporting and COs were perceiving for ET patients without high comorbidity, we selected ET patients who took fewer than five medications. ET patients who took fewer than five medications (n=24) reported a mean of 7.29±7.45 for the modified psychological suffering score, 5.92±6.41 for the unmodified psychological suffering score, and 2.57±2.06 for overall suffering. Their COs reported a mean of 7.50±6.00, 5.88±5.44, and 2.71±1.92, respectively. In this subgroup analysis, there were no significant differences between patient and CO reports (p>0.77).
To our knowledge, this is the first study to examine the experiences of ET patient suffering, COs’ perceptions of ET patient suffering, and the associations with depression for both patients and COs. Our study demonstrates that psychological suffering in ET patients, reported by both patients and COs, is a measurable entity, similar to psychological suffering in other disease contexts.17 For example, Schulz and colleagues17 found that osteoarthritis patients and dementia patients both reported a mean of 7.5 out of a possible 39 for psychological suffering; they also found that caregivers reported means of 8.7 and 11.7 for their perceptions of the suffering of their care-recipients with osteoarthritis and dementia, respectively. The means in the present study, when using the Schulz unmodified scale, were slightly lower than the means in other studies, but comparable (6.6±6.5 for ET patients and 9.0±8.2 for COs). When we looked at ET patients who had low comorbidity, their reports of psychological suffering were lower than for ET patients with high comorbidity. However, they were still well within the range of what has been reported in osteoarthritis and dementia patients. In using the modified scale, we also found that many ET patients frequently feel frustrated, suggesting that this may also be an important aspect of psychological suffering beyond anger and irritability.
The findings that COs overestimate patient psychological suffering are consistent with previous studies of osteoarthritis and dementia and demonstrate that overestimation of suffering also occurs in the context of ET.19 For example, it has been shown that caregivers of individuals with dementia consistently report greater levels of suffering and lower levels of quality of life for dementia patients than they report themselves.19 These consistent findings showing overestimation of perceived suffering suggest that clinicians should be careful in using proxy informants exclusively in their assessments. It also suggests that COs may benefit from interventions that enhance communication between patients, COs, and clinicians. On the one hand, a patient’s suffering may not be taken seriously; on the other, family members may be perceiving suffering that does not exist. This is especially important given that patient experiences and COs’ perceptions of patient suffering have been shown to have implications for both dyad members’ mental health.18 Miscommunication about suffering may also have negative effects on caregivers’ and clinicians’ support behavior.
In terms of associations with depression, multiple studies10,35 have suggested that ET patients have a higher prevalence of depression than individuals without ET. The biological basis for depression in ET is unknown at this time. One study suggested that depression could be a secondary response to the motor symptoms.14 The current study, by examining the role of psychological suffering, provides additional information about sources of depression for people with ET and their family members. As in other studies of different disease contexts, the present findings show that the experience and perception of psychological suffering may be more important than disability and clinical disease severity of ET in predicting mental health outcomes.
This study should be considered in the context of certain limitations. First, the sample size was small, which may have limited the power to detect significant effects; however, numerous significant associations were detected, which makes this unlikely. Second, the ET patients were selected because many of them were ascertained through a disease-specific organization and because they volunteered to undergo an intensive cognitive evaluation as part of the COGNET study. These patients may not be representative of the general ET patient population as they may suffer from more severe disease. However, our sample was not exclusively made up of ET cases with severe tremor; 11 participants (20.0%) were assigned tremor ratings of 1 (low amplitude) or 1.5 (only occasionally moderate amplitude) on all items of the videotaped neurological examination. Third, seven of the ET patients were diagnosed with MCI and two were diagnosed with dementia during their COGNET evaluations, so the validity of their responses to questionnaires could be questioned. However, the exclusion of these patients and their COs from the analysis did not alter our results significantly. Fourth, our measure of comorbidity, number of medications taken, was at best a surrogate marker. Finally, our study was cross-sectional so we were not able to detect directionality or causality of effects. Future studies would benefit from the inclusion of a larger, more representative sample of ET cases and their family members or friends who are followed longitudinally. These studies could also benefit from the use of the same measures of depression for ET patients and their CO. This would allow the use of dyadic models such as the Actor–Partner Interdependence Model, which takes into account the interdependence in dyad members’ responses.36
In conclusion, this study provides a new understanding of experiences and perceptions of psychological suffering in patients and COs, beyond physical disability, within the context of ET. It provides a clear link between psychological suffering and depressive symptoms in patients and their family members and friends. We hope raising awareness of the ET patients’ experiences of psychological suffering and perceptions of those who are close to them helps improve communication with clinicians and provides insight for families and other caregivers experiencing depression in the context of ET.
1 Funding: This study was funded by the National Institutes of Health: R01 NS086736. The funding body played no role in the design of the study or in the collection, analysis, or interpretation of data or in writing the manuscript.
2 Financial Disclosures: None.
3 Conflicts of interest: The authors report no conflict of interest.
4 Ethics Statement: This study was performed in accordance with the ethical standards detailed in the Declaration of Helsinki. The authors’ institutional ethics committee has approved this study and all patients have provided written informed consent.
Benito-León, J, Bermejo-Pareja, F, Morales, JM, Vega, S and Molina, JA (2003). Prevalence of essential tremor in three elderly populations of central Spain. Mov Disord 18: 389–394. doi: 10.1002/mds.10376. [PubMed]
Louis, ED and Ferreira, JJ (2010). How common is the most common adult movement disorder? Update on the worldwide prevalence of essential tremor. Mov Disord 25: 534–541. doi: 10.1002/mds.22838. [PubMed]
Seijo-Martinez, M del Rio, MC Alvarez, JRR Prado, RS Salgado, ET Esquete, JP et al. (2013). Prevalence of essential tremor on Arosa Island, Spain: a community-based, door-to-door survey. Tremor Other Hyperkinet Mov, : 3. doi: 10.7916/D89P30BB.
Bares, M, Husarova, I and Lungu, OV (2012). Essential tremor, the cerebellum, and motor timing: towards integrating them into one complex entity. Tremor Other Hyperkinet Mov, : 2. doi: 10.7916/D8P277T7.
Sternberg, EJ, Alcalay, RN, Levy, OA and Louis, ED (2013). Postural and intention tremors: a detailed clinical study of essential tremor vs. Parkinson’s disease. Front Neurol 4: 1–8. doi: 10.3389/fneur.2013.00051. [PubMed]
Louis, ED, Galecki, M and Rao, AK (2013). Four essential tremor cases with moderately impaired gait: how impaired can gait be in this disease?. Tremor Other Hyperkinet Mov, : 3. doi: 10.7916/D8QV3K7G.
Sengul, Y Sengul, HS Yucekaya, SK Yucel, S Bakim, B Pazarcı, NK et al. (2015). Cognitive functions, fatigue, depression, anxiety, and sleep disturbances: assessment of nonmotor features in young patients with essential tremor. Acta Neurol Belg 115: 281–287. doi: 10.1007/s13760-014-0396-6. [PubMed]
Gutierrez, J, Park, J, Badejo, O and Louis, ED (2016). Worse and worse and worse: essential tremor patients’ longitudinal perspectives on their condition. Front Neurol 7: 1–7. doi: 10.3389/fneur.2016.00175. [PubMed]
Rao, AK, Gilman, A and Louis, ED (2014). Balance confidence and falls in nondemented essential tremor patients: the role of cognition. Arch Phys Med Rehabil 95: 1832–1837. doi: 10.1016/j.apmr.2014.04.001. [PubMed]
Jhunjhunwala, K and Pal, PK (2014). The non-motor features of essential tremor: a primary disease feature or just a secondary phenomenon?. Tremor Other Hyperkinet Mov, : 4. doi: 10.7916/D8D798MZ.
Janicki, SC, Cosentino, S and Louis, ED (2013). The cognitive side of essential tremor: what are the therapeutic implications?. Ther Adv Neurol Disord 6: 353–368. doi: 10.1177/1756285613489591. [PubMed]
Bermejo-Pareja, F and Puertas-Martín, V (2012). Cognitive features of essential tremor: a review of the clinical aspects and possible mechanistic underpinnings. Tremor Other Hyperkinet Mov, : 2. doi: 10.7916/D89W0D7W.
Monin, Schulz R . (2010). The effects of suffering in chronically ill older adults on the health and well-being of family members involved in their care: the role of emotion-related processes. Gero Psych 23: 207–213. doi: 10.1024/1662-9647/a000024.
Schulz, R Cook, TB Beach, SR Lingler, JH Martire, LM Monin, JK et al. (2013). Magnitude and causes of bias among family caregivers rating Alzheimer disease patients. Am J Geriatr Psychiatry 21: 14–25. doi: 10.1016/j.jagp.2012.10.002. [PubMed]
Rohl, B, Collins, K, Morgan, S, Cosentino, S, Huey, ED and Louis, ED (2016). Daytime sleepiness and nighttime sleep quality across the full spectrum of cognitive presentations in essential tremor. J Neurol Sci 371: 24–31. doi: 10.1016/j.jns.2016.10.006. [PubMed]
Fahn, S and Elton, RL (1987). Members of the UPDRS Development Committee. Fahn, S, Marsden, CD, Calne, DB and Goldstein, M eds. Recent developments in Parkinson's disease. Florham Park: Macmillan Health Care Information, pp. 153–163. vol. 2
Louis, ED, Agnew, A, Gillman, A, Gerbin, M and Viner, AS (2011). Estimating annual rate of decline: prospective, longitudinal data on arm tremor severity in two groups of essential tremor cases. J Neurol Neurosurg Psychiatry 82: 761–765. doi: 10.1136/jnnp.2010.229740. [PubMed]
Louis, ED Ottman, R Ford, B Pullman, S Martinez, M Fahn, S et al. (1997). The Washington Heights-Inwood genetic study of essential tremor: methodologic issues in essential-tremor research. Neuroepidemiology 16: 124–133. doi: 10.1159/000109681. [PubMed]
Morgan, S Kellner, S Gutierrez, J Collins, K Rohl, B Migliore, F et al. (2017). The experience of essential tremor caregivers: burden and its correlates. Front Neurol 8: 1–9. doi: 10.3389/fneur.2017.00396. [PubMed]
Yesavage, JA Brink, TL Rose, TL Lum, O Huang, V Adey, M et al. (1983). Development and validation of a geriatric depression screening scale: a preliminary report. J Psychiatr Res 17: 37–49. doi: 10.1016/0022-3956(82)90033-4.
Louis, ED Barnes, LF Wendt, KJ Albert, SM Pullman, SL Yu, Q et al. (2000). Validity and test–retest reliability of a disability questionnaire for essential tremor. Mov Disord 15: 516–523. doi: 10.1002/1531-8257(200005)15:3<516::AID-MDS1015>3.0.CO;2-J. [PubMed]
Björgvinsson, T, Kertz, SJ, Bigda-Peyton, JS, McCoy, KL and Aderka, IM (2013). Psychometric properties of the CES-D-10 in a psychiatric sample. Assessment 20: 429–436. doi: 10.1177/1073191113481998. [PubMed]
Schulz, R Beach, SR Hebert, RS Martire, LM Monin, JK Tompkins, CA et al. (2009). Spousal suffering and partner’s depression and cardiovascular disease: the Cardiovascular Health Study. Am J Geriatr Psychiatry 17: 246–254. doi: 10.1097/JGP.0b013e318198775b. [PubMed]
Lemay, EP Jr, Clark, MS and Feeney, BC (2007). Projection of responsiveness to needs and the construction of satisfying communal relationships. J Pers Soc Psychol 92: 834–853. doi: 10.1037/0022-35126.96.36.1994. [PubMed]
Chandran, V, Pal, P, Reddy, J, Thennarasu, K, Yadav, R and Shivashankar, N (2012). Non-motor features in essential tremor. Acta Neurol Scand 125: 332–337. doi: 10.1111/j.1600-0404.2011.01573.x. [PubMed]