title: Central hyperexcitability as measured with nociceptive flexor reflex threshold in chronic musculoskeletal pain: a systematic review.
abstract: Chronic musculoskeletal conditions are increasingly conceived as involving altered central nervous system processing, and impaired nociceptive flexor reflex (NFR) appears to reflect altered central nervous system processing. The primary objective was to synthesize the evidence for impaired NFR in these conditions. The secondary objective was to evaluate the NFR stimuli parameters employed by reviewed studies. Electronic databases: MEDLINE, CINAHL, Embase, PEDro, Google Scholar, and Cochrane library were searched from the mid-1960s to June 2010. Experimental reports were systematically reviewed and meta-analysis (where possible) was performed. NFR thresholds and parameters of NFR stimuli were extracted. Sixteen trials were identified, 11 of which were suitable for inclusion in the meta-analysis. Compared to healthy controls, standardized mean differences in NFR threshold were significantly lower in subjects with primary headache (-0.45; 95% confidence interval [CI] -0.77 to -0.13, P=0.005), fibromyalgia (-0.63; 95% CI -0.93 to -0.34, P<0.0001), knee pain (-1.51; 95% CI -2.10 to -0.93, P<0.00001) and whiplash (-0.73; 95% CI -1.11 to -0.35, P=0.0002). Employed stimuli parameters vary between studies, with inter-pulse duration (P=0.044) being identified by multiple regression analysis as independent predictors of the variability in NFR threshold in healthy controls. The results indicate that there is evidence of central hyperexcitability in people with chronic musculoskeletal pain. Our review also suggests that shorter inter-pulse duration tends to yield smaller variability in NFR threshold. However, further research investigating optimal stimulation parameters is still warranted.
authors.affiliation: Centre of Clinical Research Excellence: Spine, Division of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland, St Lucia, QLD 4067, Australia Department of Physiotherapy, Singapore General Hospital, Singapore 169608, Singapore Centre for National Research on Disability and Rehabilitation Medicine (CONROD), Edith Cavell Building, University of Queensland, Herston, QLD 4029, Australia.
authors.forename: Edwin Choon Wyn
authors.initials: ECW
authors.lastname: Lim
authors.forename: Michele
authors.initials: M
authors.lastname: Sterling
authors.forename: Andrew
authors.initials: A
authors.lastname: Stone
authors.forename: Bill
authors.initials: B
authors.lastname: Vicenzino
mesh_terms: D016208:Databases, Factual / Q000706:statistics & numerical data; D006801:Humans; D009140:Musculoskeletal Diseases / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology*; D010146:Pain / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000502:physiology*; D011595:Psychomotor Agitation / Q000150:complications; D012018:Reflex / Q000502:physiology*