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The spiral axis as a clinical tool to distinguish essential tremor from dystonia cases

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Abstract

Background

Tremor is a common feature of a variety of neurological disorders. In genetic studies of essential tremor (ET), investigators need to screen potential enrollees by mail or telephone to exclude those with other neurological conditions, especially dystonia. In clinical settings, the differentiation of ET and dystonia may also be very challenging. We hypothesized that the spiral axis, described below, is a useful screening tool to distinguish ET cases from dystonia cases.

Methods

We analyzed the hand-drawn spirals of 135 individuals enrolled in a genetics study at Columbia University Medical Center. Each of the four spirals was assessed for the presence of a single identifiable tremor orientation axis, and a spiral axis score (range = 0–4) [a single axis on all 4 spirals] was assigned to each enrollee.

Results

There were 120 ET cases and 15 cases with dystonic tremor. Most (101/120, 84.2%) ET cases had an axis score ≥1 vs. only half (8/15, 53.3%) of the dystonia cases (p = 0.02). Receiver Operator Curve (ROC) analysis revealed that the use of a spiral axis score ≥2 as a cut off would exclude 60.0% of dystonia cases while including 67.5% of ET cases.

Conclusion

Handwritten spirals appear to have a single predominant axis in more ET than dystonia cases. The evaluation of this axis has moderate diagnostic validity as a screening tool to distinguish ET cases from those with dystonia. Although this study did not assess the utility of this tool in clinical practice settings, future studies should do so.

Introduction

Tremor is a common feature of a variety of neurological disorders, including essential tremor (ET), Parkinson's disease (PD), and dystonia [1]. In genetic studies of ET, investigators must screen potential enrollees (i.e., reportedly affected relatives) by mail or telephone to ensure that they do not have other neurological conditions. Many individuals who self-report a diagnosis of “ET” actually have another neurological disorder rather than ET [2]. One previous study on misdiagnosis of tremor disorders reported that of the 26 patients with false ET, 6 (23.1%) were diagnosed with dystonia [2]. Another study of the over-diagnosis of ET demonstrated that 4 (40%) of 10 ET patients had dystonia [3].

To save time and resources, and avoid costly field trips to individuals who do not have ET, it is important to develop methods, aside from self-report, to effectively screen/exclude individuals with dystonic tremor prior to an in-person study visit. We previously reported [4] that on spiral drawing, the wave forms of ET cases generally aligned along a single predominant axis rather than several axes (Fig. 1). To our knowledge, no study has investigated the spiral axis as a screening tool to distinguish ET from dystonia cases. Here, we analyzed the pre-enrollment hand-drawn spiral drawings of 135 individuals enrolled in a genetic study, all of whom self-reported ET. Each of the four spirals was assessed for the presence of a single identifiable tremor orientation axis, and a spiral axis score (range = 0–4) [a single axis on all 4 spirals] was assigned to each enrollee (Fig. 1). After enrollment, each enrollee underwent a neurological examination, and 120 were diagnosed with ET and 15 with dystonic tremor. We hypothesized that the spiral axis would be a useful screening tool to distinguish ET cases from dystonia cases.

Section snippets

Participants

This study was conducted as part of the Family Study of Essential Tremor (FASET), Columbia University Medical Center (CUMC), New York [5]. Prior to enrollment, individuals with familial ET who were reported to have tremor were required to submit a set of four Archimedes spirals (two right, two left), drawn on a standard sheet of paper, without resting their wrist on the paper. These were analyzed and rated by a senior movement disorders neurologist (E.D.L) to determine the features and severity

Results

There were 120 ET cases and 15 dystonia cases (6 with torticollis, 2 with arm dystonia, 1 with blepharospasm, and 6 with dystonia in more than one region). The dystonia cases had not reported a diagnosis of dystonia during the screening phase of the study – dystonia was diagnosed after enrollment based on the videotaped neurological examination. ET cases were on average 7.1 years younger than dystonia cases (p = 0.03, Table 1). The proportion of women was 50.8% in ET cases and 93.3% in dystonia

Discussion

Despite attempts to use questionnaires to screen out enrollees with dystonia, in the current study, we still enrolled 15 dystonia cases, so there is a clear need for better screening methods. This need prompted these analyses. In an earlier study, we examined hand drawn spirals in a small sample of 29 ET cases and identified an axis in one or both spirals in 23/29 cases [4]. We now explore whether a tremor axis is identifiable in dystonia patients. Our current results show that an analysis of

Acknowledgments

This work was supported by NIH grant R01 NS073872.

References (6)

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