RESUMEN
We present a description of the Central Sensitivity Syndrome (CSS) and some of its main components such as Multiple Chemical Sensitivity Syndrome, Chronic Fatigue Syndrome and Fibromyalgia. We review the changes in pain perception, describing the physiology and pathophysiology of the painful experience from the medulla horn to the CNS. We explain the theory of central sensitization as the basis to the syndrome. We refer to the differences between fibromyalgia and depressive disorders, is spite of their frequent presentation in comorbidity. We state the main clinical and neurobiological differences. We point out the main psychoneuroimmunoendocrinologic differences such as adrenal activity (hypoactivity vs. hyperactivity, DST hypersuppressive response vs. DST non suppression, hypersensitivity of central glucocorticoid receptors vs. desensitization of these, among others), thyroid (probable reverse T3 vs. flat stimuli TSH response curve) and growth hormone secretion (probable increase vs. disruption of normal circadian rhythm) that makes CSS resemble PTSD. We describe differential changes in sleep patterns (alpha-delta intrusion vs. altered sleep time, REM latency, and stage 3/4) and immunological disturbances almost opposite in each pathological entity. We finally argue which medical specialty should treat these complex syndromes.