Muscle pain in neuromuscular disorders and primary fibromyalgia

Abstract

Muscle fibre degeneration and regeneration, inflammation in intramuscular connective tissue and hypoxia in resting muscle are not necessarily associated with pain. However, when sustained or dynamic muscle contractions are performed in an ischaemic muscle, severe pain develops. In the chronic muscle pain syndrome called fibromyalgia (or fibrositis) the most likely cause of the pain is a combination of muscle tension and muscle hypoxia. This conclusion is supported by the finding of a pathological distribution of tissue oxygen tension in painful muscles and a subjective feeling of muscle tension and muscle stiffness in the majority of patients. A decrease in high energy phosphates is found in biopsies from painful muscle. The most characteristic morphological finding is the so called ragged red fibre, which is a finding that can been seen in mitochondrial disorders. The morphological and chemical findings are possibly a consequence of a long standing hypoxia. The possibility that activity in muscle sympathetic nerves is important for the development of chronic muscle pain is discussed.

Changes in muscle morphology in chronic trapezius myalgia.

“…Thus 10 female patients with a mean age of 45.5 (range 27-58) years were included. According to detailed work history recordings, these patients had been exposed to static and highly repetitive work tasks for an average of 15 (range [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] years. Their job titles were cashier (N =2), charwoman (N =l), assembly worker (N = 5), microscopist (N = I), and spray lacquerer (N = I).…”

“…Recent findings of morphological and biochemical changes in muscle biopsies from patients with work-related trapezius myalgia have been suggestedto be related to local temporary hypoxia and reduced muscle oxygenation (15), possibly due to reduced blood flow (16). Furthermore, an energy crisis within the muscle fibers has been suggestedas a possible cause of chronic muscular pain (15,17).…”

Fiber type composition of the human male trapezius muscle: Enzyme‐histochemical characteristics

“…Ragged-red fibers have been suggested to be the most characteristic morphological finding in chronic trapezius myalgia (Henriksson, 1988).…”

Load pattern and pressure pain threshold in the upper trapezius muscle and psychosocial factors in medical secretaries with and without shoulder/neck disorders

“…Ha¨gg (1991) proposed an explanatory model for shoulder myalgia based on the Henneman recruitment principle (Henneman et al 1965) and findings of single affected fibres (''ragged red fibres'') (Henriksson 1988). A practical consequence of this hypothesis is that short periods of totally relaxed muscle (EMG gaps, Veiersted et al 1990) would prevent later myalgia.…”