Essential tremor (ET) is a progressive neurological disease that can have a significant impact on patients’ activities and life satisfaction (1). Due to tremors, ET patients may experience functional disability (2) and diminished quality of life (3). Fine motor skills are particularly challenging; patients with ET often use modified utensils (4) or leave all writing tasks to a part of the day when tremors are mildest. Patients with more severe ET may be completely unable to use silverware or glassware without spilling all contents, and writing may be impossible (5). ET patients may also experience a host of additional non-tremor symptoms (6) including problems with balance (7–9), cognitive impairment compared with healthy controls (10–12), and sleep dysregulation (10, 13). Cognitive deficits are not uncommon, affecting 30–60% of patients (14), but run a wide range of severities from subclinical abnormalities to mild cognitive impairment (MCI) and dementia. Specific cognitive deficits in ET include impairments in executive function, working memory, verbal memory, and language (14, 15). Furthermore, individuals with ET also experience increased frailty as they age (16), and psychosocial factors contribute to the difficulty of dealing with ET. Many patients experience embarrassment (2, 17), anxiety (2, 17), and depression (8), with some patients meeting diagnostic criteria for social anxiety disorder and social phobia (18, 19).

Typically, the impairments due to ET are not severe enough to require constant care or paid caregivers. However, these challenges can require the assistance of relatives and friends who take on caregiving activities and act as caregivers. Patients may rely on family or friends to assist with eating, drinking, and dressing and to perform tasks such as writing checks or completing forms. In patients with voice tremors (approximated at 12% of all ET patients) (20), friends, and relatives will act as interpreters to assist the patient in being understood. Finally, ET caregivers provide emotional and psychological support. While we know that care providing can be burdensome across disease contexts, the experience of ET caregivers is unknown and is in need of exploration. In fact, a recent patient-needs assessment for ET identified “support for family members and caregivers” as an area of care that needed improvement (21).

In the literature, caregiver burden is defined as the diminishment of one’s emotional, physical, social, or financial well-being as a result of providing care (22). Caregiver burden has been well-described in patient populations that share similarities with ET, including the frail elderly (23), Parkinson’s disease (PD) (24), dementia (25), and MCI (26). In these studies, burden is associated with a pattern of patient and caregiver attributes. Typically, caregiver burden increases with disease severity and impaired patient cognition (16, 27). Additionally, large time investments by the caregiver have been found to be particularly burdensome, and both patient and caregiver mood seem to play an important role in moderating levels of caregiver burden.

This study has three aims: first, to assess the levels of caregiver burden in the ET population. Second, to determine the characteristics of both caregivers and ET patients that are correlated with burden. Based on previous work examining caregiver burden in similar populations, we hypothesize that increased tremor severity (14), longer duration of care (28), and cognitive impairment (29) will be associated with burden. Finally, previous research in multiple illness contexts has shown that caregivers who perceive their partner to be suffering experience a higher level of burden (23). Suffering as a construct is typically measured along three parameters (psychological, physical, and existential/spiritual distress) (30) and is assessed from the perspective of both the caregiver and the patient. Focusing on the dimensions of physical and psychological suffering, we will explore this relationship in the ET context. It is hypothesized that in ET as well, those caregivers who perceive more suffering experience more burden. This research aims to clarify the experiences of ET relatives and caregivers so that clinicians can provide the appropriate support and counseling.

Fifty-five pairs of ET participants and their caregivers completed all necessary questionnaires for analysis. ET participants had a mean age of 76.9 years and a mean total tremor score of 23.1 (Table 1). Most caregivers were the spouses (31, 56.4%) or children (16, 29.1%) of ET participants. Four caregivers (7.3%) were friends, and four (7.3%) had another familial relationship (long-term girlfriend, daughter-in-law, niece) with the ET participant. Caregivers were on average younger than ET participants with a mean age of 66.6 (t = −5.76, p < 0.01) (Table 1).

Caregivers perceived higher psychological suffering scores than ET participants reported (t = 2.53, p < 0.05). Caregivers perceived similar physical suffering scores to what ET participants reported (t = 1.06, p = 0.29) (Table 1).

Caregiver burden has not been previously assessed in the context of ET. This study sought to understand the level of caregiver burden in ET, to discover the clinical correlates of such burden, and to investigate the relationship between perceived patient suffering and burden.

We found that while some relatives and loved-ones of our ET participants are providing little care, others are very active caregivers. There are ET caregivers who spend a significant amount of time (up to 40 h/week) providing care and assisting their partners with 10 (out of 10) activities of daily living. On average, caregivers are helping with three of these daily living tasks, and almost half (43.6%) of all of the caregivers surveyed are assisting with writing tasks. We found as well that this caregiving can be burdensome. Our caregivers reported a mean ZBI-12 score of 6.1 ± 8.2. Other studies using the same scale to assess caregiver burden found means of 15.0–17.7 for dementia patients (46, 47), 9.6 for heart failure patients (48), 11.1–12.0 for advanced cancer patients (46, 48), and 21.7 for patients with acquired brain injury (46). Average ET ZBI-12 scores are slightly lower than in these other studied conditions. Yet, the range of ZBI-12 scores that we found in the ET population is close to matching these other conditions. The 10th–90th percentile range of ZBI-12 scores for our ET participants was 0–20.2. For heart failure patient caregivers, the 10th–90th percentile range was 0–22 (48), and for advanced cancer patient caregivers, the range was 0–24.2 (48). 12.7% of our ET caregivers reported levels of burden within the highest quartile level found by the creators of the ZBI-12 (43). This compares to findings of 30 and 19% in the lung cancer and heart failure caregiver population, respectively. While many ET caregivers do not experience much burden, we have found that there is a group who are burdened at levels that are within the range of other difficult and disabling conditions.

To our knowledge, there have been no previous studies of caregiver burden in ET, so we cannot compare our results with earlier findings. However, the patient and caregiver characteristics that correlated with burden in this study are largely in-line with research on PD caregiver burden or MCI caregiver burden. Like past studies, we found burden to be unrelated to caregivers’ age but significantly related to the amount of time and number of tasks that caregivers provided assistance (24). Predictably, years spent providing care, hours per week dedicated to caregiving, and the number of tasks with which caregivers assisted were all associated with increased reports of burden. Also in-line with previous research in the PD and MCI populations, we found that ET participants’ decreased cognition was significantly associated with increased burden for their caregivers (29). Functional cognition (assessed by the CDR) and global cognition (assessed by the MoCA) were both related to caregiver burden, and these relationships remained intact in a group of participants with normal cognition or only MCI (as defined by CDR < 1). Although one might assume tremor severity to be an important indicator of burden, we did not find associations between burden and either objective tremor severity scores (as measured by a neurologist) or subjective tremor disability scores (as reported by the ET participants). In past PD research, some studies have found caregiver burden to be connected to tremor severity and some have not (24, 49). Our results point toward the non-tremor symptoms of ET being more burdensome to caregivers than the tremor symptoms.

Our findings also suggest a relationship between depression and caregiver burden that likely warrants further exploration in the context of ET. Like past studies in other populations, we found that increased depressive symptoms in either the ET participant or in the caregiver were associated with higher burden for caregivers (24). Perhaps it is particularly burdensome for caregivers to witness their loved one experience depressive symptoms.

Similarly, we found caregiver perceptions of suffering to be strongly associated with caregiver burden whereas measures of patient impairment (total tremor score, tremor disability score) were not. These findings fit past research which describes perceived suffering as a significant predictor of caregiver burden even after adjusting for disability (50). Our data support the hypothesis that dealing with a partner’s suffering (especially psychological suffering) is difficult for caregivers and can outweigh the burden of actual tasks or tangible assistance that caregivers also provide.

This study is limited in that we did not include a group of healthy, age-matched controls, or a similar disease population. As no studies of PD or MCI have used the ZBI-12 to assess caregiver burden, we cannot compare directly to either population. A control group would have helped us to place results in an age-matched context to confirm that the results are disease specific and not merely aging related. A second limitation is that our sample came from a population of ET cases who had agreed to become brain donors, which could have biased our sample toward people with more severe tremors. However, in our analyses, we found no correlation between total tremor score and caregiver burden (r = 0.13, p = 0.33, Table 4) or between tremor disability score and caregiver burden (r = 0.05, p = 0.71, Table 4). This lack of association suggests that the potential skewing of our sample toward more severe tremor is unlikely to have affected our main results. Furthermore, our sample was not exclusively comprised of ET cases with severe tremor; 11 participants (20.0%) were assigned WHIGET tremor ratings of 1 (low amplitude) or 1.5 (only occasionally moderately amplitude) on all items of the videotaped neurological examination (36). An additional limitation of the study is that the ET cases were of advanced age and on average had the tremor for more than 30 years. Studies of ET populations with different characteristics (e.g., younger age or shorter duration) would be of value and would likely yield different results. Strengths of this study are our participants’ wide range of tremor severity and cognitive abilities and our inclusive definition of the term “caregiver.” We were able to broadly assess the burden on the relatives and friends of ET patients.

Why is caregiver burden important to consider? Research has shown that caregivers struggling with burden can be immensely impacted by their responsibilities. Burden has been repeatedly linked with a lower quality of life (51) and depression (49). Given our results, we can identify a simple and likely effective way of reducing burden. We found that perceived suffering was an important predictor of burden and also that caregivers over-reported suffering when compared with ET participants. Conversations in which caregivers are brought to understand the actual magnitude of suffering felt by ET patients would decrease perceived suffering and thus begin to reduce burden.

In conclusion, we were able to answer the three aims that this research set out to explore. We found that some caregivers of ET patients experience moderate to high levels of burden and that burden is associated with decreased cognition, the level of care providing, and depressive symptoms in patients and caregivers—but is not associated with tremor severity. Caregivers’ perception that their partners were psychologically suffering was also associated with burden and in fact, was the best predictor of caregiver burden. While not all relatives and friends of ET patients provide extensive care or experience burden, there is a group reporting high levels of caregiver burden that requires the attention and counseling of clinicians. This burden is associated with primarily non-tremor symptoms of ET and with caregivers’ perception that their partners are suffering.

The cohort of ET participants for these analyses of caregiver burden came from a larger longitudinal study of cognitive function in ET that began in July 2014 (Clinical Pathological Study of Cognitive Impairment in Essential Tremor, NINDS R01NS086736). The institutional review boards of Yale University and Columbia University approved that study, which aims to clinically and pathologically characterize a cohort of individuals with ET using motor, neuropsychiatric, and neuropsychological measures.

SM was involved in the conception and design of this work, the analysis and interpretation of data, the drafting of the manuscript, and she gives final approval of this version to be published and agreement to be accountable for all aspects of the work in question. SK was involved in the conception and design of this work, the acquisition of data, the critical revision of the manuscript, and she gives final approval of the version to be published and agreement to be accountable for all aspects of the work in question. JG was involved in the conception and design of this work, the acquisition of data, the critical revision of the manuscript, and he gives final approval of the version to be published and agreement to be accountable for all aspects of the work in question. KC was involved in the conception and design of this work, the acquisition of data, the critical revision of the manuscript, and she gives final approval of the version to be published and agreement to be accountable for all aspects of the work in question. BR was involved in the conception and design of this work, the analysis and interpretation of data, the critical revision of the manuscript, and she gives final approval of the version to be published and agreement to be accountable for all aspects of the work in question. FM was involved in the conception and design of this work, the analysis and interpretation of data, the critical revision of the manuscript, and he gives final approval of the version to be published and agreement to be accountable for all aspects of the work in question. SC was involved in the conception and design of this work, the analysis and interpretation of data, the critical revision of the manuscript, and he gives final approval of the version to be published and agreement to be accountable for all aspects of the work in question. EH was involved in the conception and design of this work, the acquisition of data, the critical revision of the manuscript, and he gives final approval of the version to be published and agreement to be accountable for all aspects of the work in question. EL was involved in the conception and design of this work, the acquisition of data, the critical revision of the manuscript, and he gives final approval of the version to be published and agreement to be accountable for all aspects of the work in question. JM was involved in the conception and design of this work, the analysis and interpretation of data, the drafting of the manuscript, and she gives final approval of this version to be published and agreement to be accountable for all aspects of the work in question.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.