Pathological mechanisms implicated in localized female trapezius myalgia

Myalgia localized to the neck and shoulder in women is a growing problem bo th in the general population and in the industrial world. The aim of this s tudy was to investigate the mechanisms involved in work-related myalgia. In 21 women (age, 38.7 +/- 5.5 years), muscle biopsies were obtained from the upper part of the trapezius and the morphologic and metabolic characterist ics of muscle fibres were analyzed. The patients indicated the number of pa inful areas on a pain drawing and the intensity of pain was assessed using a visual analogue scale (VAS). Two groups were formed on the basis of the m edian values: lower pain level and higher pain level. Trapezius muscles wer e characterized by the large size of type I fibres and the low capillary to fibre area ratio for both type I and type IIA fibres. patients with the hi ghest pain scores had the lowest capillary to fibre area ratio for type I f ibres (coefficient correlation r = -0.45 and P < 0.05). Moreover, the propo rtion of cytochrome c oxidase (COX)-negative fibres seen in the cross-secti ons was significantly higher in the group of patients which had the higher pain and more painful areas than in the group of patients with lower pain l evel and painful areas (P < 0.05). The significant increase (P < 0.05) of t he size of the type I fibres in trapezius myalgia point to the special stra in imposed upon type I muscle fibres during work tasks. Cytochrome oxidase c deficiency which is indicative of an energy crisis within muscle cells an d the low capillary to fibre area ratio which might impair oxygen delivery and removal of metabolites in the working muscles are both associated with pain in the trapezius muscle. (C) 1998 International Association for the St udy of Pain. Published by Elsevier Science B.V.