Muscle pathology in primary fibromyalgia syndrome: a light microscopic, histochemical and ultrastructural study.

Upper medial trapezius muscle biopsy was obtained from 12 primary fibromyalgia syndrome (PFS) patients (age 17 to 40 years) and studied with histochemistry, light and electron microscopy (EM). No evidence of inflammation was found in any case. Significant histochemical abnormalities were Type II fiber atrophy in 7 and moth-eaten appearance of Type I fibers in 5. EM revealed segmental muscle fiber necrosis with lipid and glycogen deposition as well as subsarcolemmal mitochondrial accumulation in all cases. Papillary projections of sarcolemmal membrane were seen in 11 patients. These observations in 12 PFS cases without obvious muscle trauma indicate definite but nonspecific muscle changes which we suspect are secondary to chronic muscle spasm and ischemia of unknown etiology.