Abstract
Background: Mild and transient head tremor may sometimes be observed in otherwise tremor-free relatives of essential tremor (ET) cases, although its prevalence is unclear. A diagnostic question is whether this transient, isolated head tremor, often observed as no more than a wobble, is an early manifestation of ET or whether it is a normal finding. A direct comparison with controls is needed.Methods: Two hundred and forty-one first-degree relatives of ET cases (FD-ET) and 77 spousal controls (Co) were enrolled in a study of ET. Each underwent a detailed evaluation that included a tremor history and videotaped neurological examination. None of the enrollees reported tremor, had a prior diagnosis of ET, or had significant tremor on screening spirals. All videotaped examinations were initially reviewed by a movement disorder neurologist blinded to subject type, and among those with head tremor on examination, co-reviewed by two additional movement disorders neurologists.Results: Twenty-six (10.8, 95% Confidence interval [CI] = 7.5–15.3%) of 241 FD-ET vs. 2 (2.6, 95% CI = 0.7–9.0%) of 77 Co had isolated, transient head tremor (odds ratio = 4.54, 95% CI = 1.05–19.57, p = 0.04). No enrollee had significant upper extremity tremor and none met inclusion criteria for ET based on the presence of upper extremity tremor. With one exception, head tremor occurred during or after phonation. It was always transient (generally a single back and forth wobble) and rare (observed briefly on one or two occasions during the videotaped examination) and had a faster frequency, lower amplitude and a different quality than voluntary head shaking.Conclusion: The basis for the observed isolated head tremor is unknown, but it could be an early feature of ET in ET families.Indeed, one-in-ten otherwise unaffected first-degree relatives of ET cases exhibited such tremor. To a far lesser extent it was also observed in “unaffected” controls. In both, it is likely a sign of early, emerging, undiagnosed ET, although follow-up studies are needed to confirm this. If it were ET, it would indicate that the prevalence of ET may be considerably higher than previously suspected.
Highlights
Essential tremor (ET) is the most common tremor disorder and among the most prevalent movement disorders (1, 2)
We previously reported that speech and certain vocal tasks can trigger a transient head tremor in ET cases (11)
We reported the prevalence of isolated head tremor in each of our two groups (FD-ET and Co), and in a logistic regression, calculated the odds of isolated head tremor in FDET compared to Co, thereby yielding odds ratios (ORs) and 95% confidence intervals (CI)
Summary
Essential tremor (ET) is the most common tremor disorder and among the most prevalent movement disorders (1, 2). In a descriptive analysis of the same studies, the median crude prevalence was 6.3% in this age group (1). In a single study of two small series of asymptomatic relatives of ET cases who had normal, physiological levels of arm tremor on examination, 1/26 (3.7%) and 6/27 (23.1%) evidenced a transient head wobble on examination during or directly after sustained phonation, speech, or reading aloud (12). Given these widely disparate results, our current estimate of the prevalence of this condition is imprecise (i.e., somewhere between 3.7 and 23.1%) (12).
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