The term “phantom limb pain” was first used by Civil War surgeons, but the syndrome actually dates back as far as the 16th Century. There was a time when phantom limb pain was thought to be psychogenic, but today experts believe both peripheral and central neural mechanisms are involved in the condition.1
There were about 1.6 million lost limbs in the United States in 2005 and that number is projected to double by 2050.1
“During the wars in Iraq and Afghanistan, there were over 16,000 limbs lost. Thankfully those numbers have gone down,” said Jack Tsao, MD, associate professor of neurology at the Uniformed Services University of the Health Sciences in Bethesda, Maryland.
Common causes of limb loss include vascular problems, trauma, and cancer. Phantom limb pain is different than stump pain, which is pain in the residual part of the amputated limb. Phantom limb pains are sensations in the part of the limb that are no longer there.1
“These sensations can range from an occasional twinge to constant pain. In about 10% of cases, the pain can be debilitating,” said James McGowan, MD, anesthesiologist and pain medicine specialist at Mercy Medical Center in Baltimore.
Phantom limb pain may be more common in upper limb loss than in leg loss, but has also been seen after loss of other body parts including the eye, tongue, nose, breast, and penis. Pain may start immediately after amputation or years later.1
“Phantom limb pain occurs in close to 90% of people who lose a limb. In many patients the pain will decrease over time, but in about 50% of patients pain continues for more than 10 years,” said Tsao.
Mechanisms of Phantom Limb Pain
Several theories may explain phantom limb pain. “Peripheral nerves near the area of amputation may become hyperexcitable and fire independently. This nerve activity may change pain reception neurons in the spinal cord, a process called spinal cord remodeling,” said McGowan.
Central mechanisms include cortical reorganization in which areas in the brain representing the amputated body part are taken over by neighboring brain areas responsible for other body parts.1
“Brain areas for the face may take over the hand,” said McGowan.
In a 2008 study reported in the journal Brain, researchers were able to demonstrate by functional MRI that patients with upper limb phantom pain had activity in the hand area of the brain activated by movement of lips. When asked to imagine hand movement, activity was seen in areas of the brain responsible for lip movement.2
“This theory is supported by phantom arm pain being generated by facial movement. Phantom leg pain may be triggered by genital areas of the brain, such as urination, defecation, and ejaculation,” Tsoa said. “The problem with the reorganization theory is that it takes time, and some people have phantom limb pain immediately after amputation.”