title: Increased levels of interstitial potassium but normal levels of muscle IL-6 and LDH in patients with trapezius myalgia.
abstract: The mechanisms behind the development of work-related trapezius pain are suggested to involve both peripheral and central components, but the specific contribution of alterations in muscle nociceptive and other substances is not clear. Female patients with chronic trapezius myalgia (N=19; TM) and female controls (N=20; CON) were studied at rest, during 20 min repetitive low-force exercise and recovery, and had their interstitial concentrations of potassium (K(+)), lactate dehydrogenase (LDH), interleukin-6 (IL-6) and collagen turnover determined in the trapezius muscle by the microdialysis technique. K(+) levels were at all time points higher in TM than in CON (P<0.0001). Baseline levels of LDH and IL-6 were similar in both groups. In response to exercise pain intensity, rated perceived exertion, and the concentrations of K(+), LDH and IL-6 increased significantly in both groups. [K(+)] immediately decreased to baseline levels in CON but remained elevated during the first 20 min of recovery in TM (P<0.01) whereafter it returned to baseline level. In all subjects taken together mean [K(+)] correlated negatively with pressure pain threshold of trapezius (P<0.001), positively with mean pain intensity VAS (P<0.001) and mean perceived exertion (P<0.001). Rises in muscle LDH and IL-6 as well as the anabolic ratio for collagen type I was not significantly different between groups. In conclusion, patients with chronic pain in the trapezius muscle had increased levels of interstitial potassium. This finding could be causally related to myalgia or secondary to pain due to deconditioned muscle or altered muscle activity pattern.
authors.affiliation: National Institute of Occupational Health, Copenhagen, Denmark Division of Rehabilitation Medicine, Department of Neuroscience and Locomotion, Faculty of Health Sciences, SE 581 85 Linköping, Sweden Sports Medicine Research Unit and Copenhagen Muscle Research Center, Bispebjerg Hospital, Copenhagen, Denmark Pain and Rehabilitation Center, University Hospital, Linköping, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Rosendal
authors.forename: Jesper
authors.initials: J
authors.lastname: Kristiansen
authors.forename: Björn
authors.initials: B
authors.lastname: Gerdle
authors.forename: Karen
authors.initials: K
authors.lastname: Søgaard
authors.forename: Michael
authors.initials: M
authors.lastname: Peolsson
authors.forename: Michael
authors.initials: M
authors.lastname: Kjær
authors.forename: Jan
authors.initials: J
authors.lastname: Sörensen
authors.forename: Britt
authors.initials: B
authors.lastname: Larsson
mesh_terms: D000328:Adult; D003094:Collagen / Q000378:metabolism*; D005260:Female; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D008875:Middle Aged; D009209:Myofascial Pain Syndromes / Q000175:diagnosis / Q000378:metabolism*; D009784:Occupational Diseases / Q000378:metabolism*; D010147:Pain Measurement; D017288:Pain Threshold; D011188:Potassium / Q000378:metabolism*; D020069:Shoulder Pain / Q000175:diagnosis / Q000378:metabolism*
chemical_list: D015850:Interleukin-6; D003094:Collagen; D007770:L-Lactate Dehydrogenase; D011188:Potassium