Pain is a highly subjective experience that is difficult to measure objectively due to its varied expression. It is defined as a complex sensory-emotional experience; it is modulated by cognitive factors and involves a broad neural system. Functional neuroimaging has helped to define that neural circuit involved in the perception, modulation and response to painful experience, both in healthy controls and in patients with acute and chronic pain disorders. However, functional activation of the so-called “pain matrix” may also be differentially modulated by sensory and emotional processing components. The latter, for example, can influence the intensity to which a stimulus is perceived as painful. Such a threshold seems to be lower in patients with clinical diagnosis of fibromyalgia (FM) and has been linked to an abnormal pattern of activation of the “pain matrix” when assessed with functional magnetic resonance imaging (fMRI), considering a “syndrome of central susceptibility.” Supporting an etiological explanation for FM, studies have noted that a significant proportion of patients with FM demonstrate this abnormal pattern of activation to stimuli of low intensity. Additionally, there is an important and significant temporal dimension to this activation pattern observed in FM patients, where areas commonly associated with the emotional experience of pain show a prolonged response to painful stimuli compared to healthy subjects. Accordingly, fMRI may assist in objectifying the experience of pain in patients with FM in response to nociceptive stimulation.
El dolor es una experiencia subjetiva difícilmente evaluable de forma objetiva por su variada expresión. Se define como una compleja experiencia sensorioemocional, modulada por factores cognitivos y que involucra un amplio sistema neural. La neuroimagen funcional ha contribuido a definir este circuito neural en controles sanos y en pacientes con un síndrome de dolor agudo o crónico implicado en la modulación, la percepción y la respuesta de una experiencia dolorosa. Sin embargo, la activación funcional de la “matriz neural” del dolor puede modularse, bien por un componente sensorial bien por un componente emocional. Este último podría mediatizar la intensidad apartir de la que un estímulo se percibe como doloroso. Este umbral parece ser menor en pacientes con diagnóstico clínico de fibromialgia (FM), pacientes que generan una anormal activación funcional del circuito neural del dolor, evaluada mediante resonancia magnética funcional (RMF), lo que se considera un síndrome de susceptibilidad central. En apoyo a esta explicación etiológica, los estudios de RMF constatan que una proporción significativa de pacientes con FM presenta una consistente y anormal activación de la “matriz neural” del dolor a estímulos de baja intensidad. Adicionalmente, se constata una importante y una significativa activación funcional con una duración temporal de activación cerebral superior a la del estímulo nociceptivo aplicado y, específicamente, en las áreas neuroanatómicas implicadas en la dimensión emocional del dolor. En consecuencia, la RMF permite observar, de manera incruenta, la anormal respuesta funcional cerebral a un estímulo nociceptivo en pacientes con diagnóstico clínico de FM.
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