(Give this to anyone who thinks you're faking it!)

Neurology. 2006 Aug 22;67(4):673-5.
Endothelial dysfunction in cold type complex regional pain syndrome.

Schattschneider J, Hartung K, Stengel M, Ludwig J, Binder A, Wasner G, Baron R.

The authors examined endothelial function in cold type chronic complex regional pain syndrome (CRPS) I using acetylcholine- and sodium nitroprusside-induced vasodilation combined with laser Doppler flowmetry in 14 patients and 10 controls. On the affected side, acetylcholine-induced vasodilation was significantly reduced in comparison to controls and the unaffected extremity. No significant differences were found after application of sodium nitroprusside. The results demonstrate impaired endothelial function in chronic CRPS I.