Phantom limb pain is pain experienced to arise from and reside in the amputated limb, hence the name, phantom limb pain. PLP is experienced by about 50-80 % after acquired limb loss. The pain can be excruciating, and chronic phantom limb pain (PLP) can have a truly devastating effect on a persons' life, affecting both physical function and quality of life. Unfortunately, phantom limb pain has proven difficult to treat both by pharmacological and non-pharmacological methods. Several treatment options have been suggested, but without showing strong research evidence for effect on PLP.
Over time, several mechanisms have been proposed to explain the occurrence of PLP, but the most cited reasons for the existence or development of phantom limb pain are theories connected to neuroplasticity, cortical reorganization and maladaptive changes due to loss of sensory input and motor control (e. g. Pons. Science, 1991). Several studies have observed that phantom limb pain is closely associated with neuroplastic changes in the somatosensory and motor cortex of the brain. Although these are maladaptive changes, the fact that the adult brain retains a neuroplastic capacity also opens a therapeutic widow of opportunity, i. e. it makes it possible to envision non-invasive therapies that exploits the principles of brain plasticity in the treatment of phantom limb pain by designing treatments that conceivably may reverse maladaptive changes and possibly reduce PLP.
Relating to this, functional activity of the affected limb, including the use of a prosthesis, has been seen to have a positive effect on PLP, and this effect is believed to be partly explained by an effect of motor activity of the remaining stump on brain cortical activity and possibly cortical reorganization (Mosely and Floor Neurorehabilitation and Neural Repair, 2012). This is also the rationale behind classical interventions such as "mirror therapy", first proposed by Ramachandran (Nature, 1995).
The present study will investigate the effect of a novel method for treatment of phantom limb pain that extends the concept of mirror therapy. This new method entails viewing a virtual limb (phantom limb) on a large screen, that "substitute" the missing limb. In short, the treatment starts with making a videorecording of the intact limb of the patient performing different predetermined movements. This recording is then digitally "flipped" and two "intact" limbs are then displayed on a large screen in front of the patient. The amputated limb is hidden below the screen. The patient is then asked to execute a set of movements with the (hidden) amputated limb, and at the same time the person will observe the phantom limb on the screen perform the exact same (prerecorded) movements. This treatment protocol is called Intensive Visual Simulation Therapy (IVS) and extends the concept of mirror therapy, where only the intact and healthy limb is performing movements and there is no motor planning or motor execution of the amputated limb.
In this project, the effect of the IVS method on reduction of phantom limb pain will be compared to "Usual Care" (UC), which will be considered the standard treatment. Persons with either unilateral upper or lower limb amputation will be included in this study. In conjunction with use of these two therapeutic approaches, advanced, neuroimaging tools (functional near-infrared spectroscopy; fNIRS) will be implemented with the purpose of investigating the neurological responses to IVS treatment. As opposed to functional magnetic resonance imaging (fMRI), the fNIRS system allows the measurement of brain activity in a more "naturalistic" setting, like when the participants "execute" movements with the phantom limb in the IVS system.
Participants in this study will be randomized to either IVS or UC treatment. Measurement of PLP and other outcome measures will be performed at baseline, after eight weeks of IVS or UC and at 2 months follow-up. Persons in the UC group shall continue with their standard treatment for this entire period (8+8 weeks). Persons in the IVS group will receive two treatment sessions per week for eight weeks and then no treatment in the follow-up period (8 weeks). The UC group will have the opportunity to receive IVS treatment after terminating their follow-up period.
