Pardo JV, et al. - In order to test the hypothesis that differences exist in female patients with fibromyalgia syndrome (FMS) and pain-free female controls with respect to the sympathetic responses, a fact that may unmask important biomarkers and factors that contribute to the etiology of FMS, researchers undertook a pilot study including 13 individuals with FMS and 11 controls to compare blood pressure (BP), skin temperature, thermogenic activity, circulating glucose, and pain sensitivity at room temperature (24°C) with that after exposure to cold (19°C). Individuals with FMS showed the convergence of the effect of cold on 4 relatively simple measures of thermogenic, cardiovascular, and metabolic activity, each regulated by sympathetic activity. This strongly suggests impaired sympathetic responses to stress among individuals with FMS that are observable and highly significant even when measured in extraordinarily small sample populations. If insufficient sympathetic responses to stress are linked to FMS, these potential clinical biomarkers of FMS may be unmasked and maximized by stress which may be related to its etiology.