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Due to diabetes, peripheral vascular disease and trauma, the tragedy of limb amputation unfortunately continues to occur too frequently. The fact that complications are common after amputation only adds to the despair and emotional stress of the procedure. Phantom limb sensations are nearly universal after amputation. In its most innocuous form, the person with the amputation is merely aware that the limb is still there and at times can even sense movement of the limb. In approximately 50% of lower limb amputations, this sensation is painful sometimes terribly so. It can occur up to one year after the amputation and can be excruciating. It is confusing to understand how something that is no longer present can be painful and much about this phenomena is poorly understood, but some points can lead us to a general understanding about pain in other conditions.
Pain is a complex sensation that is processed and experienced at many levels within the brain. Our physical body is closely associated with a conceptual body within our consciousness and represented within our brain. There is a portion of our brains that is intimately associated with sensations including pain. In this portion of the brain, a specific area represents each part of our body. Certain parts of the body that are particularly important for sensation like our hands and our faces are over-represented. When an amputation occurs, the part of the brain that is devoted to sensing that portion of the body no longer receives normal sensory input. The sensory system then undergoes reorganization; adjacent portions of the cortex involved in the sensation of other parts of the body migrate into this neglected area and the portions representing the amputated part can shift. The amount of reorganization is correlated with the degree of pain. Certain therapies that help with phantom limb pain are actually correlated with a normalization of these brain changes.
Similar changes have been cited in reflex sympathetic dystrophy above and may also be involved in a number of other painful conditions such as painful diabetic neuropathy and pain after nerve injuries. Like in the other painful syndromes, medications may only incompletely help with this.
However, Ramachadran has described a novel and interesting therapy recently. By using mirrors that can give the appearance to the person suffering from phantom limb pain, the pain can be radically reduced. The visual feedback can modulate the other senses and alter the painful phantom limb sensation. The development of this therapy is still in its infancy and it remains to be seen whether similar techniques could lead to the treatment of other painful conditions. Other researchers have done similar experiments with virtual reality techniques.
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