Objective Biomarkers or Symptom Scores for the Classification of Fibromyalgia Syndrome?

Abstract

Multiple abnormalities in pain processing have been reported in patients with chronic musculoskeletal pain syndromes including fibromyalgia (FM). These changes include mechanical and thermal hyperalgesia, decreased thresholds to mechanical and thermal stimuli (allodynia) as well as central sensitization, all of which are fundamental to the generation of clinical pain. In addition to pain, self-reported symptoms like negative mood, non-refreshing sleep, and dyscognition, are common in FM. The pathogenesis of FM is only partially understood, but peripheral tissue changes and nervous system abnormalities have been implicated. These tissue abnormalities include decreased blood flow, increased levels of muscle metabolites, and degenerative joint changes. Indirect evidence from interventions that decrease tonic peripheral impulse input in patients with FM suggest that their overall pain and hyperalgesia is dependent on signaling from deep tissues. At least some of this peripheral impulse input seems to undergo abnormal pain processing in the central nervous system including increased pain facilitation as well as inadequate pain inhibition. Thus interventions that either decrease peripheral input and/or improve central pain processing abnormalities appear to be promising strategies for FM patients. The 1990 FM classification criteria were instrumental for research that greatly improved our current understanding of FM mechanisms. These criteria required widespread pain and mechanical hyperalgesia at ≥ 11 out of 18 body sites (tender points). In 2010 new FM criteria were introduced which only require self-reported somatic and cognitive symptoms, use complex scoring algorithms, and lack any objective mechanistic assessments. This lack of objective biomarker, however, may limit the usefulness of the new FM Criteria for research and clinical practice. Overall the diagnosis as well as the treatment of FM may benefit from improved classification criteria which should include relevant disease biomarkers that are fundamental for the development and persistence of FM and other chronic musculoskeletal pain syndromes, like abnormal central nervous system processing abnormalities of nociceptive signals. Keywords: Biomarker, central sensitization, nociception, fibromyalgia, chronic pain