title: Deficient conditioned pain modulation after spinal cord injury correlates with clinical spontaneous pain measures.
abstract: The contribution of endogenous pain modulation dysfunction to clinical and sensory measures of neuropathic pain (NP) has not been fully explored. Habituation, temporal summation, and heterotopic noxious conditioning stimulus-induced modulation of tonic heat pain intensity were examined in healthy noninjured subjects (n = 10), and above the level of spinal cord injury (SCI) in individuals without (SCI-noNP, n = 10) and with NP (SCI-NP, n = 10). Thermoalgesic thresholds, Cz/AFz contact heat evoked potentials (CHEPs), and phasic or tonic (30 seconds) heat pain intensity were assessed within the C6 dermatome. Although habituation to tonic heat pain intensity (0-10) was reported by the noninjured (10 s: 3.5 ± 0.3 vs 30 s: 2.2 ± 0.5 numerical rating scale; P = 0.003), loss of habituation was identified in both the SCI-noNP (3.8 ± 0.3 vs 3.6 ± 0.5) and SCI-NP group (4.2 ± 0.4 vs 4.9 ± 0.8). Significant temporal summation of tonic heat pain intensity was not observed in the 3 groups. Inhibition of tonic heat pain intensity induced by heterotopic noxious conditioning stimulus was identified in the noninjured (-29.7% ± 9.7%) and SCI-noNP groups (-19.6% ± 7.0%), but not in subjects with SCI-NP (+1.1% ± 8.0%; P < 0.05). Additionally, the mean conditioned pain modulation response correlated positively with Cz/AFz CHEP amplitude (ρ = 0.8; P = 0.015) and evoked heat pain intensity (ρ = 0.8; P = 0.007) in the SCI-NP group. Stepwise regression analysis revealed that the mean conditioned pain modulation (R = 0.72) correlated with pain severity and pressing spontaneous pain in the SCI-NP group. Comprehensive assessment of sensory dysfunction above the level of injury with tonic thermal test and conditioning stimuli revealed less-efficient endogenous pain modulation in subjects with SCI-NP.
authors.affiliation: Sensorimotor Function Group, Hospital Nacional de Parapléjicos SESCAM, Finca "la Peraleda," Toledo, Spain Escuela de Enfermería y Fisioterapia de Toledo, Universidad de Castilla La Mancha, Toledo, Spain. S. Albu is now with the Department of Psychology, Texas A&M University, TX, USA.
authors.forename: Sergiu
authors.initials: S
authors.lastname: Albu
authors.forename: Julio
authors.initials: J
authors.lastname: Gómez-Soriano
authors.forename: Gerardo
authors.initials: G
authors.lastname: Avila-Martin
authors.forename: Julian
authors.initials: J
authors.lastname: Taylor
mesh_terms: D000328:Adult; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008875:Middle Aged; D009437:Neuralgia / Q000175:diagnosis* / Q000209:etiology* / Q000523:psychology; D010147:Pain Measurement / Q000379:methods* / Q000523:psychology; D017288:Pain Threshold / Q000523:psychology; D013119:Spinal Cord Injuries / Q000150:complications* / Q000175:diagnosis* / Q000523:psychology