Phantom pain, also called phantom limb pain (PLP), is a discomfort perceived by the region of the body that is no longer present. This was first described by a French military surgeon in the sixteenth century. Phantom limb pain is poorly understood by experts and researchers, and around 1.6 million people live with an amputated limb.
Causes of Phantom Pain
Common causes of phantom pain are vascular problems, cancer, congenital limb deficiency, and trauma. The number of traumatic amputations has increased in the military. The incidence of PLP is reported to be around 65%, with many amputees suffering long-term, recurrent pain. Recent studies show that the prevalence of phantom pain is more common among females than males and often affects upper limb amputees more.
Phantom sensations involve a tingling sensation, throbbing pain, pins-and-needles sensations, and piercing discomfort. The cause of phantom pain is not well understood, but peripheral and central neural mechanisms are among the most popular of the hypotheses of this syndrome. After amputation, peripheral nerves are severed. The massive tissue and neuronal injury results in disruption of normal nerve input signals. This leads to a constant pain sensation. Increased nerve activity and hyperexcitability among neurons can also increase certain neurotransmitter activity. Substance P, neurokinins, and tachykinins all are neurotransmitters that contribute to phantom pain.
Another proposed mechanism of PLP is based on cortical reorganization. After amputation, the brain areas change, and reorganization occurs in the cortical regions. With the body schema concept, there is an area of the brain that continues to perceive pain long after the stump has healed. The neuromatrix is a network of neurons within the brain that integrates numerous inputs from various areas. This region of the brain is affected with amputation and phantom pain.
Phantom Pain Treatment
The treatment of phantom pain may involve a combination of therapies. Treatment options include:
- Epidural analgesia – An intrathecal pain pump can be surgically implanted into the patient’s body. A small tube runs from the tiny unit to the spinal cord space. Tiny amounts of medication are delivered to the spinal cord, which gives an analgesic effect. In a recent study, epidural analgesia started soon after surgery had the greatest pain relief effects. In a review of 28 clinical studies, intrathecal opioid delivery was found to have an 87% success rate.
- Oral medications – Nonsteroidal anti-inflammatory drugs (NSAIDs) were found to be effective for PLP. These drugs inhibit the enzymes needed for prostaglandin synthesis, which decreases pain perception. Opioids have also proven effective in randomized controlled trials. Certain antidepressants (desipramine and nortriptyline) are effective for nerve pain and have been showing useful in clinical studies involving phantom pain. Finally, anticonvulsants, such as gabapentin, have been somewhat useful for treating PLP.
- Transcutaneous electrical nerve stimulation (TENS) – This is a small battery-operated device worn outside the body. Wires run from the unit and attach to electrodes placed along the spine. The unit delivers the electrical current that interferes with pain signals. The sensation is described as pleasant. In a recent clinical study involving patients with neuropathic pain, TENS was found to be significantly better for pain reduction than placebo.