Is fibromyalgia a neuropathic pain syndrome?

The fibromyalgia syndrome (FM) seems an unlikely candidate for classification as a neuropathic pain. The disorder is diagnosed based on a compatible history and the presence of multiple areas of musculoskeletal tenderness. A consistent pathology in either the peripheral or central nervous system (CNS) has not been demonstrated in patients with FM, and they are not at higher risk for diseases of the CNS such as multiple sclerosis or of the peripheral nervous system such as peripheral neuropathy. A large proportion of FM sufferers have accompanying symptoms and signs of uncertain etiology, such as chronic fatigue, sleep disturbance, and bowel/bladder irritability. With the exception of migraine headaches and possibly irritable bowel syndrome, the accompanying disorders are clearly not neurological in origin. The impetus to classify the FM as a neuropathic pain comes from multiple lines of research suggesting widespread pain and tenderness are associated with chronic sensitization of the CNS. An examination of how the term neuropathic pain is defined reveals a conceptual split into 2 partially overlapping groups of disorders: those with demonstrable pathology in the nervous system and those characterized primarily by enduring dysfunction in the nervous system. Requiring demonstrable pathology in the nervous system in the definition of neuropathic pain is the traditional approach. The expansion of the definition to require only enduring nervous system dysfunction is less palatable because it opens the classification to many disorders of uncertain etiology, including complex regional pain syndrome. As it is uncertain which of the many different chronic pain syndromes include an enduring component of central sensitization, restricting the term "neuropathic pain" to those disorders with a primary etiology clearly related to the peripheral or CNS is prudent and consistent with clinical practice.