Abnormalities of fibromyalgia pain processing: use of magnetic resonance spectroscopy as a window to the brain

Abstract

Introduction: Fibromyalgia (FM) is a musculoskeletal pain disorder whose pathogenesis is only partially understood. Although most FM patients complain of pain in muscles and joints, few specifi c tissue abnormalities have been detected. Several recent studies have reported evidence of central pain amplifi cation in these patients associated with increased levels of substance P and nerve growth factor in the spinal fl uid. These abnormalities are most likely the result of sensitized wide-dynamic and nociception-specifi c neurons in the dorsal horn of FM patients. Central sensitization can be maintained by low-intensity peripheral input from muscles and joints activating nociceptive and nonnociceptive pathways, ultimately resulting in augmented responses of central pain processing neurons in the spinal cord and brain. These central mechanisms underlying amplifi ed pain responses can be explored using a number of advanced brain imaging techniques that include functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy (MRS). MRS is a noninvasive method to measure levels of brain tissue metabolites, including N-acetylaspartate (NAA), choline, creatine, and lactate [1]. These chemicals can provide important information on the health of brain tissues, overall energy status, and metabolism. Because brain levels of creatine are usually constant, they are typically used as internal standards, allowing for comparison of NAA/creatine and choline/creatine between groups. Other metabolites that can be observed by MRS include glucose, myoinositol, glutamine, glutamate, glycine, and many others. MRS only requires standard anatomic MRI using specifi c pulse sequences that can be obtained with most commercially available scanners.