Abstract
Complex regional pain syndrome (CRPS) is a chronic neuropathic pain disorder that typically occurs in the limbs, usually the upper limb. CRPS usually develops from a peripheral event but its maintenance relies on changes within the central nervous system. While functional abnormalities in the thalamus and primary somatosensory cortex (S1) of the brain are some of the most consistently reported brain findings in CRPS, the mechanisms are yet to be explored in full, not least of all how these two regions interact and how they might relate to clinical deficits, such as the commonly reported poor tactile acuity in this condition. This study recruited 15 upper‐limb CRPS subjects and 30 healthy controls and used functional magnetic resonance imaging (fMRI) to investigate infra‐slow oscillations (ISOs) in critical pain regions of the brain in CRPS. As hypothesised, we found CRPS was associated with increases in resting signal intensity ISOs (0.03–0.06 Hz) in the thalamus contralateral to the painful limb in CRPS subjects. Interestingly, there was no such difference between groups in S1, however CRPS subjects displayed stronger thalamo‐S1 functional connectivity than controls, and this was related to pain. As predicted, CRPS subjects displayed poor tactile acuity on the painful limb which, interestingly, was also related to thalamo‐S1 functional connectivity strength. Our findings provide novel evidence of altered patterns of resting activity and connectivity in CRPS which may underlie altered thalamocortical loop dynamics and the constant perception of pain.
Highlights
Complex regional pain syndrome (CRPS) is a chronic pain disorder characterised by spontaneous or regionally evoked pain and other signs and symptoms typically affecting the distal extremities, the upper limbs (Marinus et al, 2011)
In addition to chronic neuropathic pain being associated with altered thalamic burst firing and altered thalamocortical rhythm (Di Pietro et al, 2018; Jones, 2010; Sarnthein, Stern, Aufenberg, Rousson, & Jeanmonod, 2006; Walton, Dubois, & Llinas, 2010; Walton & Llinás, 2010), we have recently shown that neuropathic pain in the orofacial region is characterised by significantly increased infra-slow oscillations (ISOs) (
For the 3 CRPS subjects with pain on the left, their functional magnetic resonance imaging (fMRI) images were reflected across the midline so that the right side was ipsilateral to the highest ongoing upper limb pain
Summary
Complex regional pain syndrome (CRPS) is a chronic pain disorder characterised by spontaneous or regionally evoked pain and other signs and symptoms typically affecting the distal extremities, the upper limbs (Marinus et al, 2011). There are several lines of evidence of central nervous system involvement. These include the observation that the pain often spreads in a non-dermatome fashion (van Rijn et al, 2011), that pain intensity of the initial injury, but not injury severity, predicts the development of CRPS (Moseley et al, 2014), as well as the presence of perceptual deficits including altered two-point discrimination ability (Galer & Jensen, 1999a; McCabe, Haigh, Halligan, & Blake, 2003; Moseley, 2005).
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