Capillary Structure and Mitochondrial Volume Density in the Trapezius Muscle of Chronic Trapezius Myalgia, Fibromyalgia and Healthy Subjects

Abstract

Objective: To better understand some of the pathophysiological mechanisms of chronic muscle pain. Methods: Muscle biopsies were obtained from myalgic areas in the trapezius muscle of female patients suffering from either chronic trapezius myalgia or fibromyalgia and from corresponding areas in healthy, symptom-free subjects. Electron microscopy and morphometric analysis were used to determine mean myofibrillar mitochondrial density and the capillary structure. Results: The mitochondrial fraction was higher in the patients with chronic trapezius myalgia than in those with fibromyalgia or in the healthy subjects. The mean volume density of mitochondria in the trapezius muscle fibers, however, was lower than that previously reported for human female limb muscle in all three groups. This indicates that the trapezius muscle in general has a lower capacity to tolerate endurance work than limb muscles. The morphometric analysis of the capillary structure revealed that the area and thickness of the endothelium was significantly larger in the fibromyalgia group than in the patients with chronic myalgia and in the healthy subjects. Capillaries with structural changes in the endothelium were more frequent in the fibromyalgia group of patients than in the other two groups; the differences in frequency, however, were not significant. Conclusions: It is proposed that the higher mitochondria fraction in chronic trapezius myalgia might be a result of an insufficient capillarization of the fibers in these patients. The capillary changes in the fibromyalgic group might be secondary to disturbances in muscle microcirculation causing localized hypoxia/ischemia. Thus, the present result might indicate differences in the pathophysiology of chronic myalgia and fibromyalgia.

KEYWORDS:

• Trapezius myalgia
• fibromyalgia
• morphology