Fibromyalgia is a painful stress-related disorder. A key issue in fibromyalgia research is to investigate how distress could be converted into pain. The sympathetic nervous system is the main element of the stress response system. In animal models, physical trauma, infection, or distressing noise can induce abnormal connections between the sympathetic nervous system and the nociceptive system. Dorsal root ganglia sodium channels facilitate this type of sympathetic pain. Similar mechanisms may operate in fibromyalgia. Signs of sympathetic hyperactivity have been described in this condition. Genetic factors and/or distressful lifestyle may lead to this state of sympathetic hyperactivity. Trauma and infection are recognized fibromyalgia triggers. Women who suffer from fibromyalgia have catecholamine-evoked pain. Sympathetic dysfunction may also explain nonpain-related fibromyalgia symptoms. In conclusion, in fibromyalgia, distress could be converted into pain through forced hyperactivity of the sympathetic component of the stress response system. 1. Introduction The key issue in fibromyalgia (FM) research is to define why people suffering from this illness have so much pain. FM is a stress-related disorder [1]. Patients who have FM often associate the onset of their illness to a particularly stressful situation such as physical or emotional trauma [2–4] or to different types of infections [5]. Additionally, they are frequently immersed in a distressful life style [6]. This article reviews scientific evidence suggesting that, in FM, distress becomes pain through malfunction of the sympathetic component of the stress response system. The following topics will be analyzed. (i)Definition of stress, distress, and allostasis.(ii)The sympathetic nervous system as a key element of the stress response system.(iii)The autonomic nervous system as a complex adaptive system.(iv)Animal models linking the development of sympathetic pain to physical or emotional trauma and to different types of infections.(v)Dorsal root ganglia sodium channels as key elements in sympathetically maintained pain.(vi)Physical and emotional distress in FM.(vii)Genetic and clinical data suggesting that FM is a sympathetically maintained neuropathic pain syndrome. (viii)Conclusions. 2. Stress, Distress, and Allostasis The term stress is used in various ways and has different interpretations. Stress has been used to describe the cause (stressor) or the effect (stressed) of a phenomenon. An acceptable physiological definition of stress could be “any stimuli, physical or emotional, that threatens
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