Cognitive impairment in cervical dystonia: core clinical feature or secondary effect related to non-motor symptoms?

AIM OF THE STUDY: To investigate subtle cognitive dysfunction in patients with cervical dystonia (CD) as a potential independent non-motor feature of the disease or as a consequence of interactions between motor and other non-motor symptoms (NMS). CLINICAL RATIONALE FOR THE STUDY: Cognitive impairment represents one of the most common non-motor symptoms in patients with cervical dystonia. However, the interrelations between cognitive dysfunction, motor symptoms, and other non-motor symptoms remain insufficiently explored. MATERIAL AND METHODS: Patients with CD (n = 34) underwent comprehensive assessment at baseline and 4-6 weeks after botulinum toxin (BoNT) treatment. Clinical and sociodemographic variables, as well as motor and non-motor symptoms of dystonia were assessed. Matched controls (n = 33) underwent a single assessment. Cognitive function, depressive and anxiety symptoms, and sleep disturbances were assessed by a neuropsychologist in both groups. RESULTS: At baseline, 52.9% of patients with CD scored below the Montreal Cognitive Assessment (MoCA) cut-off for cognitive impairment, compared with 3.0% of healthy controls. Patients also showed higher rates of depressive symptoms, anxiety, and sleep disturbances. Cognitive performance was significantly lower in the CD group across multiple domains [executive functions, visuospatial abilities, language, memory, and attention (p < 0.05)]. Following botulinum toxin treatment, significant improvements were observed in overall MoCA scores and in specific domains of executive function, visuospatial abilities, language, and memory (p < 0.05). No correlation was found between overall dystonia severity and cognitive performance, although executive function correlated with motor symptom severity at baseline (R = -0.41, p = 0.017). In the multivariate model, sleep disturbances were identified as the strongest negative predictor of cognitive function (β = -0.40, p = 0.006), while higher education showed a protective effect. Other variables, including depression, anxiety, age, disease duration, and dystonia severity, were not significant predictors. CONCLUSIONS AND CLINICAL IMPLICATIONS: The study explores cognitive impairment in cervical dystonia in relation to motor severity and non-motor domains, with the multivariable model suggesting a potential role of sleep disturbances. The findings do not allow a definitive distinction between cognitive impairment as a core feature of dystonia or a secondary effect related to non-motor symptoms, but they indicate complex and interdependent mechanisms.