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

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).

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.

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.

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.

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.