Central representation of chronic ongoing neuropathic pain studied by positron emission tomography

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Abstract
S with painful mononeuropathy (PMN, i.e., pain in the distribution of a nerve, neuralgia) with positron emission tomography (PET), using regional cerebral blood flow (rCBF) as an index for neuronal activity. Eight patients (29–53 years) with PMN in the lower extremity (4 in the right, 4 in the left) were recruited. Paired comparisons of rCBF were made between the patient's habitual pain (HP) state and the pain alleviated (PA) state following a successful regional nerve block (RNB) with lidocaine. The ongoing neuropathic pain resulted in activation of bilateral anterior insula, posterior parietal, lateral inferior prefrontal, and posterior cingulate cortices as well as the posterior sector of the right anterior cingulate cortex (ACC), Brodmann area (BA) 24, regardless of the side Of PMN. In addition, a reduction in rCBF was noted in the contralateral posterior thalamus. No significant change of rCBF was detected in the somatosensory areas, i.e., Sl and SII. The cerebral activation pattern, while addressing the differences between the HP and PA states, emphasises the affective-motivational dimension in chronic ongoing neuropathic pain. The striking preferential activation of the right ACC (BA 24), regardless of the side of the PMN, not only confirms that the ACC participates in the sensorial/affectional aspect of the pain experience but also suggests a possible right hemispheric lateralisation of the ACC for affective processing in chronic ongoing neuropathic pain. Our data suggests that the brain employs different central mechanisms for chronic neuropathic pain and experimentally induced acute pain, respectively. *Corresponding author: Martin Ingvar, M.D., Ph.D., Department of Clinical Neuroscience, Section of Clinical Neurophysiology, Karolinska Hospital, 171 76 Stockholm, Sweden. Tel.: (46) 8-7295134; FAX: (46) 8-339953 E-mail: martini@neuro.ks.se (Received 5 January 1995; accepted 1 February 1995.) © Lippincott-Raven Publishers....