Experimental forearm immobilization in humans induces cold and mechanical hyperalgesia

Background: Complex regional pain syndrome is a painful condition of unknown etiology. Clinical and experimental observations suggest that limb immobilization may induce symptoms and signs characteristic of complex regional pain syndrome. This study examined the effect of forearm immobilization on regional sensory and autonomic functions in healthy subjects. Methods: Thermal and mechanical sensitivity, skin temperature, and vasoconstrictor responses were measured in 30 healthy subjects before and 0, 3, and 28 days after scaphoid cast immobilization. Fifteen subjects served as nonimmobilized controls. Results: At cast removal, 27 subjects experienced pain at joint movement. Cast immobilization induced cold hyperalgesia in glabrous and hairy skin on the immobilized hand and induced significant skin temperature differences between the control and the immobilized hand at cast removal and after 3 days. Immobilization also reduced pain threshold at skin fold testing at all time points after cast removal. All measures except pain threshold at skin fold testing were normalized after 28 days. Immobilization did not affect thermal detection, heat pain, and pressure pain thresholds; resting skin perfusion; or vasoconstrictor responses induced by mental stress or deep inspirations. Conclusions: Four weeks of forearm immobilization caused transient changes in skin temperature, mechanosensitivity, and thermosensitivity, without alteration in the sympathetically mediated vascular tone.