Head tremor at disease onset: an ataxic phenotype of cervical dystonia

Abstract

Background: Cervical dystonia (CD) can present with head tremor. It is unclear whether ataxic features are differentially associated with this phenotype at onset of CD.

Objectives: We sought to evaluate: (1) the demographic features of CD patients with (Tr-CD) and without head tremor (nTr-CD) at onset, and (2) the differential ataxic features between these CD subtypes.

Methods: For the first objective, we compared demographic data in Tr-CD versus nTr-CD subtypes in the entire cohort of CD subjects enrolled in the Dystonia Coalition Natural History and Biorepository studies (n = 1608). For the second objective, we rated the standardized videos from consecutively enrolled Tr-CD subjects (n = 50) and age-, gender-, and disease duration-matched nTr-CD subjects (n = 50) for ataxia severity scoring using the Scale for the Assessment and Rating of Ataxia (SARA) and the International Cooperative Ataxia Rating Scale (ICARS); and for dystonia severity using the Toronto Western Spasmodic Torticollis Rating Scale section-I (TWSTRS) and the Global Dystonia Rating Scale (GDRS).

Results: Of 1,608 subjects, 18.1% (n = 291) were classified as Tr-CD and 81.9% (n = 1317) as nTr-CD. The Tr-CD cohort was older, predominantly female, and had longer disease duration than the nTr-CD cohort (p = 0.01). Compared to nTr-CD, Tr-CD subjects had worse generalized ataxia, speech, and gait and posture scores. High ataxia severity with low dystonia severity distinguished Tr-CD from nTr-CD with high accuracy (area under the curve, 0.91 (95% CI 0.85-0.97).

Conclusions: Head tremor at disease onset represents a clinically distinguishable subtype of cervical dystonia affecting predominantly older women, with worse ataxia and milder dystonia than the non-tremulous dystonic phenotype.

Keywords: Ataxia; Cerebellum; Dystonia; Head tremor; Tremor.

Fig. 1.. Comparison of Ataxia and Dystonia Scores in CD Subtypes

NTr-CD: Non-tremor-dominant Cervical Dystonia; Tr-CD: Tremor-dominant Cervical Dystonia; SARA: Scale for the Assessment and Rating of Ataxia; ICARS: International Cooperative Ataxia Rating Scale; TWSTRS: Toronto Western Spasmodic Torticollis Rating Scale; GDRS: Global Dystonia Rating Scale

Fig. 2.. Ataxia and Tremor Sub-scores in CD Subtypes

NTr-CD: Non-tremor-dominant Cervical Dystonia; Tr-CD: Tremor-dominant Cervical Dystonia; ICARS: International Cooperative Ataxia Rating Scale; Tremor: Composite score of items 11–14 of the ICARS; * = p < 0.05

Fig. 3.. Receiver Operator Curve

Sensitivity and Specificity Values in Differentiating Tr-CD and NTr-CD using the combination of TWSTRS and ICARS. ROC: Receiver Operator Curve; AUC: Area Under the Curve; ICARS: International Cooperative Ataxia Rating Scale; TWSTRS: Toronto Western Spasmodic Torticollis Rating Scale