Modifying the visual aspect of a virtual arm that is felt as one's own using immersive virtual reality (VR) modifies pain threshold in healthy subjects but does it modify pain ratings in chronic pain patients? Our aim was to investigate whether varying properties of a virtual arm co-located with the real arm modulated pain ratings in patients with chronic arm/hand pain due to complex regional pain syndrome (CRPS) type I (without nerve injury) or peripheral nerve injury (PNI). CRPS (n=9) and PNI (n=10) patients were immersed in VR and the virtual arm was shown at four transparency levels (transparency test) and three sizes (size test). We evaluated pain ratings throughout the conditions and assessed the virtual experience, finding that patients with chronic pain can achieve levels of ownership and agency over a virtual arm similar to healthy participants. All seven conditions globally decreased pain ratings to half. Increasing transparency decreased pain in CRPS but did the opposite in PNI, while increasing size slightly increased pain ratings only in CRPS. We conclude that embodiment in VR can decrease pain ratings in chronic arm pain, while the type of pain determines which strategy to decrease pain is most useful. We discuss this through the interactions between body image and pain perception.
