Age at Onset Predicts Motor and Non‐motor Severity in Cervical Dystonia

Background Cervical dystonia (CD) is the most common focal dystonia and shows significant heterogeneity in both motor and non‐motor symptoms. Although motor symptoms typically prompt clinical presentation, non‐motor features are the principal determinants of quality of life. Previous efforts to classify CD have focused on selected motor and non‐motor clinical characteristics, suggesting distinct subtypes with potential prognostic implications. Objective We employed cluster analysis to identify phenotypic subgroups within a large CD population with detailed motor and non‐motor assessments. Methods Adult patients with idiopathic isolated CD were included. Data were collected across five domains using validated instruments: motor severity (TWSTRS2‐Severity), quality of life (CDIP‐58 total and EQ‐5D‐5L utility index), disability (TWSTRS2‐Disability), pain (TWSTRS2‐Pain), and psychiatric symptoms (HADS‐Total). Hierarchical cluster analysis using Ward's linkage method was performed to identify phenotypic subgroups. Results 201 CD patients (67% female) were included for analysis. Median age was 62 years. Hierarchical cluster analysis identified two distinct phenotypic subgroups (Clusters A and B). Cluster A patients (n = 78) demonstrated significantly earlier disease onset (35 vs 48 years) and greater symptom burden across all variables ( p < 0.001) when compared with Cluster B (n = 123). The largest between‐cluster differences were observed for CDIP‐58, HADS‐Total, and TWSTRS2‐Pain. Motor severity showed a smaller effect size, suggesting non‐motor features more strongly distinguish these phenotypes. Conclusion Hierarchical cluster analysis identified two distinct CD phenotypes: an earlier onset high‐burden subgroup and later onset low‐burden subgroup. These clusters were primarily distinguished by non‐motor features (quality of life, mood, pain, and disability). Our findings highlight age at onset as a key determinant of CD phenotype.