Mean sustained pain levels are linked to hemispherical side-to-side differences of primary somatosensory cortex in the complex regional pain syndrome I

Abstract

Chronic back pain as well as phantom-limb pain is characterized by a close relationship between the amount of cortical reorganization and the magnitude of pain. In patients with positively assessed complex regional pain syndrome type I (CRPS I), we found a positive correlation between representational changes of primary somatosensory cortex (SI) and mean sustained pain levels. We investigated seven right-handed patients with CRPS I of one upper limb by means of somatosensory evoked potential (SSEP) mapping. Cortical representation of the CRPS-affected hand was significantly smaller than that of the contralateral healthy hand, giving rise to a substantial side difference. Subjective pain levels experienced over the last 4 weeks were estimated according to the visual analogue scale (VAS). Individual expansion of hand representation contralateral to the CRPS-affected limb was significantly correlated with mean pain intensity. Accordingly, low pain levels were linked to small representational side-to-side differences, while subjects with a distinctive hemispherical asymmetry reported the highest pain levels. Follow-up studies using functional imaging methods might be instrumental in providing a better understanding of this issue.

Functional Imaging of Central Nervous System Involvement in Complex Regional Pain Syndrome

“…43 The MC representation corresponding to the unaffected hand was significantly larger compared with the representation corresponding to the affected hand. These findings resembled the representational asymmetries in S1 20,24,31,32 and might be explained by the close anatomic and functional relationship between MC and S1. [44][45][46][47] The MC representational asymmetry was discussed with respect to chronic pain, though no direct relationship between the amount of interhemispheric asymmetry and pain intensity could be established.…”

“…Using a different methodologic approach, Pleger et al 31 used EEG to localize dipole sources of somatosensory-evoked potentials (SEP) after electrical stimulation of the median and ulnar nerve in patients with CRPS I. Results were similar to the results observed in the MEG studies after tactile finger stimulation: After electrical stimulation of the median and ulnar nerve, they found a significantly smaller distance between dipole sources of the N20 SEP component, which are generated in area 3b of S1, after stimulation of the nerves at the affected hand compared with the unaffected hand.…”

Pain and Plasticity: Is Chronic Pain Always Associated with Somatosensory Cortex Activity and Reorganization?

“…Similarly, it has been reported that painful carpel tunnel syndrome is associated with an increased representation of the painful digits (Napadow et al, 2006) and use-dependent enlargements of cortical representations, including those in response to increased innocuous tactile stimulation, have been shown to occur in many sensory systems (Hodzic et al, 2004). In contrast, complex regional pain syndrome, a non-deafferented pain condition, is associated with contraction of the relevant cortical representation (Maihöfner et al, 2003;Pleger et al, 2004), although this condition involves significant decreases in the use of the painful region, which may itself affect S1 organization. Thus, both the extent and direction of cortical reorganization associated with different forms of chronic pain are highly variable, strongly suggesting that pain itself does not result in S1 reorganization.…”

“…Using SPM8 (Friston et al, 1995) and FreeSurfer (Pleger et al, 2004) software, each subject's T1-weighted anatomical image set was spatially normalized to the Montreal Neurological Institute (MNI) template and segmented into gray, white, and CSF images. Using the gray-matter images, the left and right postcentral gyrus (S1) were automatically isolated in each individual subject.…”

Altered neurocognitive processing of tactile stimuli in patients with Complex Regional Pain Syndrome (CRPS)

“…Decrements in tactile spatial discrimination in CRPS patients 5 have been associated with neuroplasticity involving shrinkage of the somatosensory cortical homunculus 5 , which physical treatments can plausibly remedy [5][6][7][8][9][10] . Shrinkage of Penfield's homunculus would be consistent with reduced tactile perceptual resolution and an increased rate of tactile misperceptions.…”