Certain patients with a possible contribution of the
sympathetic system to pain may not fit the definition of complex
regional pain syndromes (CRPS), which raises the question of
terminology for those patients. To further clarify the relationship
between the sympathetic system and pain, apart from the need for
placebo studies, there remains an urgent need for a satisfactory
definition of the criteria for a complete sympathetic block. It also
remains uncertain whether a change in the discharge pattern of
sympathetic fibres underlies the changes in sympathetic organ
function, often found in patients with CRPS.