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

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.