Lancet
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Complex regional pain syndromes can be relieved by sympathetic blockage. The mechanisms of sympathetically maintained pain (SMP) are unclear. We aimed to establish the effect of physiological sympathetic cutaneous vasoconstrictor activity on pain and hyperalgesia in patients with complex regional pain syndromes. ⋯ We have shown that in complex regional pain syndromes with SMP, physiological activation of cutaneous vasoconstrictor neurons projecting to the painful arm or leg enhances spontaneous pain and hyperalgesia. We postulate that there is a pathological interaction between sympathetic and afferent neurons within the skin.
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Susceptibility to malignant hyperthermia is diagnosed by contracture test, which requires an open muscle biopsy sample. We postulated that intramuscular injection of caffeine increases local carbon dioxide pressure (pCO(2)) in individuals susceptible to malignant hyperthermia but not in those who are non-susceptible or in healthy individuals. ⋯ There were no systemic side-effects. Metabolic monitoring of the highly diffusible CO(2) stimulated by caffeine might allow a minimally invasive test for susceptibility to malignant hyperthermia.