Sensory and pain modulation profiles of central neuropathic ongoing extremity pain in multiple sclerosis

Abstract

Prevalence of pain in multiple sclerosis (MS) patients ranges from 29% to 86%, and central ongoing neuropathic extremity pain (CNEP) is most frequently described. A prospective cohort study was aimed at evaluation of sensory and pain modulation profiles in a well-defined group of MS patients suffering from CNEP. A group of 56 MS patients suffering from CNEP that complied with the criteria of definite neuropathic pain were compared with two control groups: a painless MS group (n = 63) and a group of 73 healthy volunteers, age- and sex-matched with the pooled MS group (mean age 36.3 vs. 37.7 years, 66.7% vs. 68.9% women in controls vs. pooled MS patients). Pain questionnaires and standardized quantitative sensory testing (QST) protocol and its dynamic variant (dQST) assessing both the facilitatory (temporal summation) and inhibitory (conditioned pain modulation) pain mechanisms were used to characterize pain and to compare sensory profiles of evaluated subgroups. In the CNEP group, QST disclosed significantly more severe and frequent sensory loss (predominantly in thermal modalities) as compared to both painless MS and control groups. In addition, thermal and pressure pain hypersensitivity in both CNEP and painless MS subgroups in comparison with healthy controls were found. dQST showed no difference between CNEP and painless MS patients or controls. To conclude, in CNEP MS patients we found signs of sensory loss (as an indicator of deafferentation secondary to lesion in the spino-thalamocortical pathways) in combination with thermal and mechanical hypersensitivity due to supposed central pain mechanisms.