Background
Despite its high prevalence, there are surprisingly few prospective, longitudinal data on the clinical course of essential tremor (ET). Patients themselves often want to know from their treating physician whether and by how much their tremor is expected to worsen over time.
Methods
As part of two research protocols, prospective, longitudinal data were collected on tremor severity in two samples of ET cases (44+39 cases, combined n=83). At a baseline and one follow-up evaluation, a detailed clinical assessment was performed and action tremor in the arms was rated by a senior movement disorders neurologist using a standardised clinical rating scale (Total Tremor Score (TTS), range 0–36).
Results
In the first case sample, TTS increased annually by 0.32±0.89 points (ie, an annual increase of 5.3±17.1% (median 1.8%) from the mean baseline score). TTS increased by ≥0.5 points in 23/24 (95.8%) cases followed for ≥5 years. In the second sample, TTS score increased annually by 0.64±1.49 points (annual increase of 3.1±8.1% (median 2.0%) from the mean baseline score). TTS increased by ≥0.5 points in 11/15 (73.3%) cases followed for ≥5 years. No baseline factors were identified that predicted annual change in TTS.
Conclusions
Most ET cases exhibited a progressive worsening in tremor scores with time such that the average annual increase in tremor severity from baseline was estimated to be between 3.1% and 5.3% and the median annual increase from baseline was between 1.8% and 2.0%. These published estimates will hopefully be a useful prognostic guide for clinicians and their patients.
In nine ET brains with upper-extremity rest tremor, neither Lewy body-containing neurons nor Lewy neurites were found on α-synuclein immunostained sections, and other pathological changes in the basal ganglia were minimal. These data support the notion that isolated rest tremor in longstanding ET is not the expression of underlying Lewy body pathology in the SNc.
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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