Neuroendocrine and immune aspects of fibromyalgia

Fibromyalgia is a form of non-articular rheumatism characterised by long term (>3 months) and widespread musculoskeletal aching, stiffness and pressure hyperalgesia at characteristic soft tissue sites, called soft tissue tender points. The biophysiology of fibromyalgia, however, has remained elusive and the treatment remains mainly empirical. This article reviews the neuroendocrine-immune pathophysiology of fibromyalgia. There is no major evidence that fibromyalgia is accompanied by activation of the inflammatory response system, by immune activation or by an inflammatory process. There is some evidence that fibromyalgia is accompanied by some signs of immunosuppression, suggesting that immunomodifying drugs could have potential in the treatment of fibromyalgia. Recent trials with cytokines, such as interferon-alpha, have been undertaken in patients with fibromyalgia. Immunotherapy with these agents, however, may induce symptoms reminiscent of fibromyalgia and depression in a considerable number of patients. Lowered serum activity of prolyl endopeptidase (PEP), a cytosolic endopeptidase that cleaves peptide bonds on the carboxyl side of proline in proteins of relatively small molecular mass, may play a role in the biophysiology of fibromyalgia through diminished inactivation of algesic and depression-related peptides, e.g. substance P. Trials with PEP agonists could be worthwhile in fibromyalgia. The muscle energy depletion hypothesis of fibromyalgia is supported by findings that this condition is accompanied by lowered plasma levels of branched chain amino acids (BCAAs), i.e. valine, leucine and isoleucine. Since there is evidence that BCAA supplementation decreases muscle catabolism and has ergogenic values, a supplemental trial with BCAAs in fibromyalgia appears to be justified.