[Sympathetic nervous system and pain: ideas, hypotheses, models.]

In the present article aspects of reflex sympathetic dystrophy (RSD) and sympathetically maintained pain (SMP) are discussed from the point of view of a basic scientist. The main focus is on the sympathetic nervous system. A critical evaluation of the clinical situation is followed by an explanation of the components of a general hypothesis about the mechanisms that might operate in these pain syndromes. This discussion centres on the couplings which might develop between sympathetic and primary afferent neurons, the changes in the neuroeffector transmission to the autonomic effector organs, the role of the micromilieu of the nociceptors and the changes of the central signal in the sympathetic neurons. Finally, clinical observations are discussed that seem to bear little or no relation to the models that are available. The general synopsis puts the problem into a wider context.