Objective:  Here, we hypothesised that somatosensory abnormality in patients with dystonia relates to a more general deficit in pre-attentive error/deviant detection . 

Background: Dystonia is a common movement disorder, characterised by abnormal postures of the affected body part. This overt motor phenotype has overshadowed a range of non-motor symptoms, in particular somatosensory abnormalities that have more recently been the focus of study, but it is currently unclear how abnormal somatosensory integration relates to the pathophysiology of dystonia

There are an enormous number of stimuli competing for our limited conscious resources at any one time. It would thus seem highly important to have a system that is at a pre-attentive stage capable of detecting salient change in the environment and biasing attentional focus towards this change. Mismatch negativity is a negative component of the event related potential (ERP) occurring at about 150-250ms and is calculated by subtracting the ERP from a standard repeated stimulus from that produced by a rare “oddball” stimulus. Error or deviation detection, which this task probes, is likely to be of fundamental evolutionary importance(ref.).

Against this background, we hypothesised that patients with cervical dystonia would have abnormal, reduced somatosensory MMN.

Methods: To assess patients with dystonia and controls using a mismatch negativity paradigm (MMN), where evoked potentials generated in response to a standard repeated stimulus are subtracted from the responses to a rare “odd ball” stimulus. We assessed MMN for “somatosensory” and “auditory” stimuli in patients with cervical dystonia and healthy age matched controls.

Results: Eighteen patients with adult-onset primary cervical dystonia were recruited. Eighteen healthy age and gender matched controls were also examined (Patient: 6 men and 12 women, mean age 58.8 ±11.7 years; Control: 7 men and 11 women, mean age 55.2± 10.9 years). There was a reduction in peak amplitude of somatosensory MMN(mean difference control-dystonia:-1.0 µV±0.3, p<0.00, t=-3.1). Auditory MMN was normal in dystonia (mean difference control-dystonia:-0.2 µV±0.2, p=0.24, t=-1.2) (Table 1).

Conclusions: These results suggest that pre-attentive error/deviant detection, specifically in the somatosensory domain, is abnormal in dystonia, and that this may contribute to the fundamental pathophysiology in dystonia.

References: Garrido MI, Kilner JM, Stephan KE, Friston KJ. The mismatch negativity: a review of underlying mechanisms. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology 2009;120(3):453-463.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/somatosensory-mismatch-negativity-is-abnormal-in-cervical-dystonia/