Changes of trapezius muscle blood flow and electromyography in chronic neck pain due to trapezius myalgia

Chronic neck pain may increase the transmitter activity of neuropeptides in the upper cervical medulla causing impairment of the blood flow in the loc al muscle because of a lack of vasodilatatory substances excreted axonally. We have been using a new single-fibre technique for clinical determination of the microcirculation (LDF) in the trapezius muscles in relation to elec tromyography (EMG). This study pertains to the 76 patients (46 women and 30 men) who received a final diagnosis of chronic trapezius myalgia out of a total series of 300 cases with chronic neck pain which had been remitted to the National Insurance Administration Hospital in Tranas, Sweden, because their complaints interfered with their working ability. The purpose was to derive more objective medical information upon which to base rehabilitation . Sixty percent had continuous pain and 40% had pain after physical effort, or at work. Twenty healthy women volunteered to participate as a normal co ntrol group. The right and left trapezius muscles of all individuals were e xamined simultaneously with laser-Doppler flowmetry (LDF) and surface EMG d uring a fatiguing series of stepwise-increased contractions, each of 1 min duration with 1 min rest in between. The most painful side was compared wit h the opposite side in all patients and, in the female patients, also with the right shoulder of the healthy control women. The patients showed consis tently low local blood flow in the painful side. The difference was statist ically significant at low contraction intensities. Muscle tension was somew hat elevated, as evidenced by a slight increase of the rms-EMG that was sta tistically significant at high contraction intensities. The mean power freq uency (MPF) of the EMG showed no change. The lowered local blood flow was n ot explained by a changed intramuscular pressure which is low in the trapez ius during ordinary activities that do not normally impair the local blood flow (Larsson, S-E., Cai, H. and Oberg, P.A., Microcirculation in the upper trapezius muscle during varying levels of static contraction, fatigue and recovery in healthy women. A study using percutaneus laser-Doppler flowmetr y and surface electromyograpy, fur. J. Appl. Physiol., 66 (1993) 483-488). We conclude that an impaired regulation of the microcirculation in the loca l muscle is of central importance in chronic trapezius myalgia, causing noc iceptive pain which can be differentiated objectively from neuralgic neck-s houlder pain by the atraumatic technique described. (C) 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.