Nociceptive pathway function is normal in cervical dystonia: a study using laser-evoked potentials

Abstract

Cervical dystonia (CD) is often associated with pain in the neck muscles, though the mechanisms underlying pain in this condition are still largely unknown. The aim of this study was to assess laser pain rating and CO(2) laser-evoked potentials (LEPs) in CD patients with pain in the posterior neck region. We assessed the N2/P2 LEP complex and laser pain rating in a group of 20 CD patients and in 21 normal subjects. In 11 of the 20 CD patients (group I), the N2/P2 complex was recorded after stimulation of the skin overlying the right and left deltoid muscles (painless and non-dystonic). In the remaining nine CD patients (group II), the N2/P2 complex was recorded after stimulation of the skin over the splenius capitis muscle (painful and dystonic) and after stimulation of the skin overlying the contralateral splenius muscle (painless and non-dystonic). In group I patients, the N2/P2 LEP amplitude and laser pain rating after stimulation of both shoulders did not differ significantly from those obtained in normal subjects. Similarly, in group II patients, the N2/P2 LEP amplitude and laser pain rating after stimulation of the painful and dystonic splenius capitis muscle did not differ significantly from those obtained from either the contralateral painless, non-dystonic splenius capitis or normal subjects. The results of this study demonstrate that cutaneous nociceptive pathway function in CD patients is normal, thereby indicating that muscle pain in CD is not associated with any central sensitization of nociceptive inputs in either painful (dystonic) or non-painful (non-dystonic) body areas.

Pain processing in functional and idiopathic dystonia: An exploratory study

“…The normality of pain thresholds and tolerance in our CD sample parallels these early findings, obtained with pressure painful stimuli, and supports the view that at least cutaneous nociceptive pathways are normal in patients with idiopathic CD chronically treated with BoNT. Overall, they are in keeping with the evidence that the amplitude of the N2/P2 peak of laser‐evoked potentials is comparable between CD and healthy subjects, regardless of stimulating a painful or painless area …”

“…Pain is a frequent feature associated with CD; it occurs in up to 88.9% of patients naïve to BoNT and is correlated with severity of dystonic symptoms . Whether pain in CD is related to chronic muscle contraction or is generated by an alteration of transmission and processing of nociceptive stimuli has been a matter of debate for a long time . Several sensory modalities have been explored in idiopathic isolated dystonia.…”

“…3 Whether pain in CD is related to chronic muscle contraction or is generated by an alteration of transmission and processing of nociceptive stimuli has been a matter of debate for a long time. 8,[18][19][20] Several sensory modalities have been explored in idiopathic isolated dystonia. One of the most frequently reported alterations is prolonged temporal tactile discrimination threshold, which is a feature common to different types of dystonia, regardless of the affected body segment.…”

“…Yet, there are no experimental data on pain perception in either F‐Dys or idiopathic CD, which is often associated to pain. Only one study utilizing laser‐evoked potentials has revealed that the function of nociceptive pathways in CD is comparable to healthy subjects …”

“…Only one study utilizing laser-evoked potentials has revealed that the function of nociceptive pathways in CD is comparable to healthy subjects. 8 Based on the evidence that in F-Dys there is abnormal connectivity between motor and limbic areas, 9 we hypothesized an alteration of the cognitive-emotional component of pain in F-Dys. On the other hand, patients with idiopathic dystonia have abnormal temporal processing of somatosensory stimuli 10 and a distorsion of cortical maps in the somatosensory cortex, 11 which might produce an alteration of the sensorydiscriminatory component of pain.…”