RR394 - Development of functional magnetic resonance imaging (fMRI) to measure the central nervous system response to chronic back pain

Aim of Investigation: To investigate evidence of brain hyper-responsivity and cortical reorganization in response to actual and anticipated pain using fMRI in patients with chronic low back pain vs. healthy controls.

Methods: 17 healthy controls and 20 chronic lower back pain patients were tested. To determine whether patients (vs. controls) were hypersensitive to actual (but clinically nonspecific) pain we applied noxious thermal stimulation to the right hand and mechanical stimulation to the lower back. Innocuous warm stimulation of the hand was also tested. To determine whether patients activate more in response to visual cues signalling expected vs anticipated clinicallyrelevant pain we presented coloured visual cues to the patient prior to lifting the patient's leg to an elevation predetermined to cause discomfort and slight pain. Random effects group analyses are reported at a threshold of Z > 2.3, P <.01 (corrected) unless otherwise stated.

Results: Patients (vs controls) demonstrated significantly more activation of the contralateral parietal and prefrontal cortex in response to painful (and non-painful) thermal stimulation (vs rest) of the right hand plus ipsilateral activation of the anterior cingulate and insula cortices. An enlarged cortical reorganization of the somatosensory representation of the back following mechanical stimulation was observed with a medial shift of activation from healthy controls to patients. Finally, significantly more activation in response to a visual cue signalling expected painful movement of the leg (vs unexpected movement) was seen in right parietal and prefrontal cortices and the primary sensorimotor representation of the leg.

Conclusions: Cortical hyper-responsiveness is seen in response to actual and anticipated painful stimulation in patients with NSLBP vs. healthy controls in regions of the brain known to represent the sensory and emotive processing of pain and may suggest patients attend more generally to pain or to cues signalling pain (even in the absence of painful stimulation). Furthermore, the somatosensory region corresponding to the lower back is enlarged, which may suggest re-organisation of the brain in response to long-term pain or increased attention to this part of the body.

This work was part-funded by a grant from the Pain Relief Foundation.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.

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Updated 2021-04-19