Here is a new theory of what causes CRPS:
Reports suggest that muscles lack oxygen and skin oxygenation is impaired in Complex Regional Pain Syndrome (CRPS).
While CRPS might be related to tissue ischemia-reperfusion, the affected limb is often hyperperfused, suggesting that oxygen extraction is severely impaired instead. In a recent paper in Pain, we speculate that capillary flow disturbances may explain this peculiarity, and could contribute to the development and maintenance of CRPS.
even in normal tissue, there is considerable variability in the transit time of blood through capillaries (capillary transit time heterogeneity; CTH), and some capillaries may be perfused at flow rates that are too high to permit oxygen to be extracted by tissue. Tissue oxygenation can therefore be limited by high flow rates and if a situation arises where capillary flow patterns are not controlled an ‘oxygen shunt’ may result – so-called capillary dysfunction.
We propose that acute tissue injury causes capillary dysfunction because high interstitial pressure compresses capillaries, byproducts of blood breakdown cause pericyte constriction, and inflammatory mediators enhance blood cell adhesion to the endothelium.
A critical consequence of capillary dysfunction is that blood flow and CTH combined can become so high that vasodilation fails as a means of maintaining tissue oxygenation. In this case, normal flow, and flow responses, must be suppressed in order to allow more efficient extraction of oxygen across all capillaries
We propose that the finding of hyperemic, yet hypoxic, tissue in CRPS represents the failure to suppress normal vasodilatory responses to tissue hypoxia. The suppression of blood flow to maintain tissue oxygenation in capillary dysfunction comes at a high cost: It appears to be mediated by reactive oxygen species (ROS) release, which attenuates vasodilation, but also causes long-term damage to tissue microvessels, including capillaries.
According to this hypothesis, in order to avoid prolonged oxidative stress and the development of permanent capillary damage, tissue swelling must be reduced as soon as possible after injury. We speculate that the use of corticosteroids and Vitamin C (a ROS scavenger) may reduce the risk of developing CRPS by targeting these disease mechanisms
Capillary dysfunction and impaired tissue oxygenation in complex regional pain syndrome: a hypothesis. Pain, 155 (10), 1922-6 PMID: 24946228