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Abstract
Background Essential tremor (ET) is among the most misdiagnosed neurological diseases, and overdiagnosis is especially common. As many as 30–50% of supposed ‘ET’ cases have other diagnoses, with dystonia prominent among these. Therefore, the recognition of differences in tremor phenomenology has potential diagnostic value for practising clinicians. There is an anecdotal sense that head tremor in ET is positional rather than resting, a feature which could aid in the diagnosis, yet no published data exist.
Methods In this cross-sectional study of ET and spasmodic torticollis (ST) patients (3:1 matching) who had head tremor while upright, the prevalence of supine (ie, resting) head tremor was compared.
Results There were 60 ET cases and 19 ST cases with head tremor while seated. When supine, head tremor persisted in only 5/60 (8.3%) ET versus 13/19 (68.4%) ST cases (p<0.001), indicating that essential head tremor is more likely to resolve in the supine position than is the head tremor of ST. Supine head tremor, when present in ET, did not seem to preferentially occur in patients with more severe disease (p>0.05).
Conclusions These results indicate that there is some validity to the anecdotal sense that head tremor in ET is a postural tremor that dissipates when a patient lies down; by contrast, in ST, head tremor more often persists. In a clinical context, these results have potential implications in diagnostically ambiguous patients with head tremor. Physicians should consider asking their tremor patients to lie down to assess whether head tremor resolves.
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Introduction
Essential tremor (ET) is one of the most misdiagnosed neurological diseases, and overdiagnosis is especially common. By some estimates, as many as 30–50% of supposed ‘ET’ cases have other diagnoses, especially dystonia and Parkinson's disease.1 2 ET and dystonia patients, in particular, may have overlapping clinical features. For example, head (ie, neck) tremor often occurs both in patients with ET and in those with spasmodic torticollis (ST),3 and at times (eg, when head tremor is not associated with twisting movements or head deviation and when hand tremor is mild), there can be considerable diagnostic uncertainty. Therefore, the recognition of differences in tremor phenomenology has potential diagnostic value for practising clinicians.
The presence in ET of postural arm tremor, coupled with the low prevalence of rest tremor in that disease, has led to an anecdotal sense that head tremor in patients with ET,4 which is exhibited while the head is not supported against gravity (in an upright position), will dissipate when patients lie in the supine (resting) position. However, we are not aware of any published data that substantiate this, showing that head tremor resolves when ET patients are recumbent. In dystonia patients, dystonic postures and tremor may continue in limbs and body regions that are at rest, and it is presumed that head tremor in patients with ST may persist when patients are supine. Yet we are unaware of any data comparing ET patients with ST patients in this regard. Our aim in this observational, cross sectional study was to compare ET and ST patients, all of whom had head tremor while seated, in terms of the prevalence of supine head tremor. Furthermore, we determined whether supine head tremor, like the resting arm tremor of ET, preferentially occurs in ET patients with severe disease.5
Methods
ET cases were all enrolled as potential future brain donors in a clinical research study at Columbia University Medical Center (CUMC) (2009–2011), and their ascertainment has been described previously.6 Of 175 enrolees, 60 were observed on videotaped neurological examination to have head tremor while seated and they were the subject of this study. Twenty ST patients, also ascertained from CUMC, were consecutively enrolled after their routine clinical visit to the Center for Parkinson's disease and Other Movement Disorders, if they met inclusion criteria (head tremor observed on examination during their clinical visit). There was no attempt to age match ET or ST cases as there were no a priori data suggesting that supine head tremor would be associated with age. A consent form approved by the CUMC institutional review board was signed by all ET and ST participants on enrolment. The clinical diagnosis of ET, initially assigned by treating neurologists, was confirmed using clinical research criteria, as described previously.7 The clinical diagnosis of ST, initially assigned by treating neurologists, was confirmed according to diagnostic criteria proposed by Fahn.8 All ET and ST patients underwent the same in-person clinical assessment that included structured clinical questionnaires and a standardised videotaped tremor examination. The videotaped examination included three tests of kinetic arm tremor performed with each hand (drinking water from a cup, finger–nose–finger manoeuvre and a spiral drawing task) as well as assessments of voice tremor (sustained phonation, reading aloud) and head tremor while seated and then while comfortably lying on their back for 2 min with their head fully supported against gravity.
Videotapes were reviewed by a senior neurologist specialising in movement disorders (EDL) who rated the severity of tremor. An arm kinetic tremor score (range 0–24) was generated by summing the 0–4 ratings of kinetic tremor during three right and left hand tests noted above; the mean rating of arm kinetic tremor (range 0–4) was the average tremor rating during the three right hand and three left hand tests. Head tremor was evaluated separately while seating and while supine using the Fahn, Tolosa and Marin rating scale,9 resulting in head tremor scores (0 (non-existent)–4 (severe)) while seated and while supine.
We had a fixed number (n=60) of ET cases enrolled between 2009 and 2011. Estimating a priori that supine head tremor might be observed in only 30% of ET cases and as many as 70% of ST cases, in 2011 we planned a targeted enrolment of 20 ST cases (3:1 matching), which we calculated would provide 90% power to detect a difference between ET and ST in terms of the proportion with supine head tremor (assuming α=0.05).
Results
All 60 ET cases and 19 (95.0%) of 20 ST cases had head tremor that was observed while they were seated during the videotaped examination. The remaining analyses included these 79 subjects. The 60 ET cases were older than the 19 ST cases (p<0.001) but were similar in terms of gender. Tremor duration was longer in ET than in ST, and a larger proportion of ET than ST cases had voice tremor (table 1). As expected, ET and ST cases differed with respect to the use of sensory tricks, feelings of head twisting and treatment with botulinum toxin, and ET cases had greater arm kinetic tremor than ST cases (table 1).
Demographic and clinical characteristics of essential tremor and spasmodic torticollis cases
ET cases had higher head tremor scores while seated than did the ST cases (table 1, p=0.02). When supine, head tremor persisted in <10% of ET cases versus two-thirds of ST cases (table 1, p<0.001). The mean head tremor score while supine was greater in ST than in ET cases (table 1, p=0.001). The change in head tremor score from seated to lying was greater in ET cases than in ST cases (table 1, p<0.001). Head tremor resolved completely in six (31.6%) of 19 ST cases on lying down; it diminished in eight (42.1%) and stayed the same in five (26.3%). It did not worsen in any cases.
There were five ET cases (all women) whose head tremor persisted while they were supine. None of the five noted a feeling of head twisting. We compared them with the 55 ET cases whose head tremor resolved when they were supine. The two groups were similar with respect to age (87.2±5.3 vs 84.8±4.8; t=1.05, p=0.30), mean arm kinetic tremor score (13.0±3.6 vs 12.3±2.7; t=0.40, p=0.69) and mean rating of arm kinetic tremor (2.1±0.5 vs 2.2±0.6; t=0.40, p=0.69). The proportion with rest tremor in their arms was as follows: four (80.0%) of five versus 31 (56.4%) of 55 (Fisher's exact test, p=0.39). Head tremor scores while seated were on average 0.6 points higher in the five cases, but due to the small sample size, the difference was not statistically significant (2.60±0.55 vs 1.98±0.87; t=1.55, p=0.13). The five ET cases also had an older age of tremor onset (60.6±23.9 vs 40.9±22.0 years; t=1.90, p=0.06) and a shorter disease duration (26.6±22.1 vs 44.0±22.7 years; t=1.64, p=0.11). The two groups were similar with respect to the proportion with voice tremor on examination (p=0.64).
There were 13 ST cases whose head tremor persisted while they were supine. We compared them with the six ST cases whose head tremor resolved when they were supine. The two groups were similar with respect to age (56.8±13.1 vs 65.0±19.8; t=1.08, p=0.30), gender (11 (84.6%) vs 4 (66.7%) women, Fisher's exact test p=0.56), head tremor scores while seated (1.58±0.34 vs 1.75±0.88; t=0.63, p=0.54), mean arm kinetic tremor score (8.7±3.9 vs 6.9±5.3; t=0.82, p=0.43) and mean rating of arm kinetic tremor (1.5±0.7 vs 1.2±0.9; t=0.82, p=0.43). None had rest tremor in their arms. The 13 ST cases had a younger age of tremor onset (30.9±19.9 vs 40.7±21.0 years; t=0.99, p=0.34) but similar disease duration (25.9±16.3 vs 24.3±27.1 years; t=0.16, p=0.87). The two groups were similar with respect to the proportion with voice tremor on examination (p=1.0).
Discussion
These results indicate that there is some validity to the anecdotal sense that head tremor in ET is a postural tremor that dissipates when a patient lies down (ie, it dissipates at rest); by contrast, in patients with ST, head tremor more often persists. In a clinical context, these results have potential implications in diagnostically ambiguous patients with head tremor. Physicians may ask these patients to lie down to assess whether the head tremor resolves. Marked abatement of head tremor in the supine position may help a treating physician assign a diagnosis of ET. Alternatively, little or no change in head tremor severity when going from a seated to a supine position, in collusion with other factors if present (eg, dystonic postures, jerkiness or non-regularity to the tremor), may indicate an ST diagnosis.
A small group of ET cases had head tremor that persisted when they were supine (ie, head tremor at rest). Rest tremor also occurs in the arms of some advanced ET cases.5 Our ET cases with resting head tremor had marginally more marked head tremor while seated and 80% also had rest tremor in their arms.
The focus of this report was head tremor in ET and ST cases, among whom head tremor often occurs. Head tremor may occur in patients with Parkinson's disease as well, although this is less commonly reported. Interestingly, in one study of five Parkinson's disease patients with head tremor, the tremor persisted in all of the patients while they were supine.10
There are potential limitations. Firstly, ET and ST patients differed by age. However, the presence of supine head tremor in ET was not associated with age, so this age difference could not have confounded our results. Secondly, ET cases were a group of future brain donors and their tremor phenomenology might not be representative of all ET cases, so that observations from other case samples would add to the literature as well. The study also had strengths, including the uniformity of approach to the patients and the attempt for the first time to collect and present empirical data to answer a question of clinical diagnostic relevance.
In summary, the data from this study indicate that essential head tremor is more likely to resolve in the supine position when compared with head tremor caused by ST. This observation may be of clinical diagnostic value in certain settings.
Acknowledgments
The authors thank Paul Greene, MD, Columbia University, for referring patients and for providing critical comments on this manuscript.
Footnotes
Funding This research was supported by the National Institutes of Health Grant R01 NS39422 (EDL).
Competing interests None.
Ethics approval The study was approved by Columbia University Medical Center Internal Review Board.
Provenance and peer review Not commissioned; externally peer reviewed.