from fibromyalgia patients. Int J Tissue React. 2005;27(3):75-82. Ribel-Madsen S, Gronemann ST, Bartels EM, Danneskiold-Samsoe B, Bliddal H. The Parker Institute, Department of Rheumatology, Frederiksberg Hospital, H:S University Hospital, Denmark. [log in to unmask] PMID: 16372472 The distribution and amount of collagen in skin from a non-tender-point area from fibromyalgia patients was assessed by quantitative analysis of amino acids and by electron and light microscopy. Skin biopsies were obtained from the front of the thigh of 27 females who fulfilled the American College of Rheumatology criteria of fibromyalgia and from eight control subjects who were matched for gender, age and physical activity. Amino acids were determined by high-performance liquid chromatography. Electron and light microscopic investigations were carried out to examine tissue structure. Among the collagen-related amino acids, the mean number of hydroxyproline residues per 1,000 residues was 52.5 and 63.4 in fibromyalgia patients and control subjects, respectively (p = 0.050); proline residues were 81.7 and 110.0 (p = 0.006); and hydroxylysine residues were 14.7 and 10.1 (p = 0.002). The total amount of skin protein in proportion to dry tissue weight was 83.4% and 72.6% in fibromyalgia and controls, respectively (p = 0.037). The overall microscopic picture was normal. The lamellar structure of the perineurium and a deficiency in collagen packing in the endoneurium was observed more frequently and to a larger extent in fibromyalgia patients than in controls. In conclusion, there are some differences between the amino acid composition of skin proteins in fibromyalgia patients compared with controls. The amount of collagen may be lower in skin from fibromyalgia patients, and collagen packing in the endoneurium may be less dense.