Phantom limb pain – Definition
Phantom limb pain (PLP) refers to ongoing painful sensations that seem to be coming from the part of the limb that is no longer there. The limb is gone, but the pain is real. The onset of this pain most often occurs soon after surgery. It can feel like a variety of things, such as burning, twisting, itching or pressure. It is often felt in fingers or toes. It is believed that nearly 80 percent of the amputee population worldwide has experienced this kind of pain.
The length of time this pain lasts differs from person to person. It can last from seconds to minutes, to hours, to days. For most people, PLP diminishes in both frequency and duration during the first six months, but many continue to experience some level of these sensations for years. People are often reluctant to tell anyone that they are experiencing PLP or phantom limb sensations, for fear that they will be considered “crazy.” However, it is important to report these pains as soon as you begin to experience them so treatment can be started.
Despite, the phantom limb sensation was described by French military surgeon Ambroise Pare (1510-1590) in the sixteenth century, even today we do not have a clear explanation of this complex phenomenon and, therefore, the pathophysiology is explained by a wide range of mechanisms. These mechanisms. which are the basis of theories, they are not necessarily mutually exclusive
Peripheral Nerve Changes
During the amputation, there is a significant amount of trauma that occurs in the nerves and surrounding tissues. This damage disrupts the normal afferent and efferent signals involved with the missing limb. The proximal portions of the severed nerves start to sprout neuromas, and the nerves become hyper-excitable due to an increase in sodium-channels and resulting in spontaneous discharges.
Spinal Cord Changes
In the spinal cord, a process called central sensitization occurs. Central sensitization is a process where neural activity increases, the neuronal receptive field expands, and the nerves become hypersensitive. This is due to an increase in the N-methyl-D-aspartate, or NMDA, activity in the dorsal horn of the spinal cord making them more susceptible to activation by substance P, tachykinins, and neurokinins followed by an upregulation of the receptors in that area. This restructuring of the neural components of the spinal cord can cause the descending inhibitory fibers to lose their target sites. The combination of increased activity to nociceptive signals as well as a decrease in the inhibitory activity from the supraspinal centers is thought to be one of the major contributors to phantom limb pain.
Over the past few years, there has been significant research into cortical reorganization and is a commonly cited factor in phantom limb pain. During this process, the areas of the cortex that represent the amputated area are taken over by the neighboring regions in both the primary somatosensory and the motor cortex. Cortical reorganization partially explains why nociceptive stimulation of the nerves in the residual limb and surrounding area can cause pain and sensation in the missing limb. There is also a correlation between the extent of cortical reorganization and the amount of pain that the patient feels.
Chronic pain has been shown to be multi-factorial with a strong psychological component. Phantom limb pain can often develop into chronic pain syndrome and for treatment to have a higher chance of success the patient’s pain behaviors and pain processing should be addressed. Depression, anxiety, and increased stress are all triggers for phantom limb pain.
What Causes Phantom Limb Pain?
Unlike pain that is caused by trauma directly to a limb, PLP is thought to be caused by mixed signals from your brain or spinal cord. This is an important concept to consider, because the treatment for this pain has differences from the treatment you would receive for other kinds of pain. New therapies for PLP all involve trying to change the signals from your brain or spinal cord.
As with any other kind of pain, you may find that certain activities or conditions will trigger PLP. Some of these triggers might include:
- Urination or defecation
- Sexual intercourse
- Cigarette smoking
- Changes in barometric pressure
- Herpes zoster
- Exposure to cold.
If you notice any particular thing triggering an episode of PLP for you, let your healthcare provider know. Some triggers can be avoided – for example, you can prevent constipation or stop smoking. For other triggers, you will just have to understand and treat accordingly. You will not be able to prevent the barometric pressure from changing, but you will be able to understand that your PLP might be more severe on days with big shifts in the weather!
People are often reluctant to tell anyone that they are experiencing PLP or phantom limb sensations, for fear that they will be considered “crazy.” However, it is important to report these pains as soon as you begin to experience them so treatment can be started.
What are the risk factors for phantom limb pain?
Anyone who has an amputation can develop phantom pain. Some people find the pain is worse when they aren’t wearing a prosthetic device.
These factors may trigger phantom limb pain:
- Angina (chest pain due to low oxygen to the heart).
- Changes in temperature or barometric pressure.
- Shingles (herpes zoster).
- Sex or physical touch.
What Phantom Limb Pain Feels Like?
Not all pain feels the same. The throbbing of a headache, for example, is very different from the sharp ache of a stomach cramp. So it’s no surprise that phantom limb pain is not the same for everyone. Your pain may feel like it’s:
- Like “pins and needles”
- Like an electric shock
Aside from pain, you may also sense other feelings from a body part that’s no longer there:
Complications of phantom limb pain
- One of the main complications of phantom limb pain is difficulty sleeping.
- Lack of sleep can worsen pain, so it is important to address PLP and sleep disturbances to prevent additional or worsened pain.
- Another major complication of phantom limb pain involves emotional changes. Depression often accompanies chronic pain, including PLP.
- The quality of life of individuals with phantom limb pain is often compromised due to impairment of daily activities and an increase in anxiety and depression.
How is Phantom Limb Pain Diagnosed?
There is no medical test to diagnose phantom limb pain. However, doctors identify the condition from the patient’s symptoms and circumstances, such as trauma or surgery, prior to the onset of the pain.
Finding a treatment to relieve your phantom pain can be difficult. Doctors usually begin with medications and then may add noninvasive therapies, such as acupuncture.
More-invasive options include injections or implanted devices. Surgery is done only as a last resort.
Although no medications specifically for phantom pain exist, some drugs designed to treat other conditions have been helpful in relieving nerve pain. No single drug works for everyone, and not everyone benefits from medications. You may need to try different medications to find one that works for you.
Medications used in the treatment of phantom pain include:
Over-the-counter (OTC) pain relievers. Acetaminophen (Tylenol, others), ibuprofen (Advil, Motrin IB, others) or naproxen sodium (Aleve) might relieve phantom pain. Take these medications only as directed by your doctor. Overuse can cause serious side effects, such as stomach bleeding.
Antidepressants. Tricyclic antidepressants may relieve the pain caused by damaged nerves. Examples include amitriptyline, nortriptyline (Pamelor) and tramadol (Conzip, Ultram). Possible side effects include sleepiness, dry mouth and blurred vision.
Anticonvulsants. Epilepsy drugs — such as gabapentin (Gralise, Neurontin) and pregabalin (Lyrica) — may be used to treat nerve pain. Side effects may include dizziness, sedation and mood changes.
Narcotics. Opioid medications, such as codeine and morphine, may be an option for some people. Taken in appropriate doses under your doctor’s direction, they may help control phantom pain.
However, you may not be able to take them if you have a history of substance abuse. Even if you don’t have a history of substance abuse, these drugs can cause many side effects, including constipation, nausea, vomiting or sedation.
N-methyl-d-aspartate (NMDA) receptor antagonists. This class of anesthetics works by binding to the NMDA receptors on the brain’s nerve cells and blocking the activity of glutamate, a protein that plays a large role in relaying nerve signals.
In studies, NMDA receptor antagonists ketamine and dextromethorphan helped relieve phantom pain. Side effects of ketamine include mild sedation, hallucinations or loss of consciousness. No side effects were reported from the use of dextromethorphan.
As with medications, treating phantom pain with noninvasive therapies is a matter of trial and observation. The following techniques may relieve phantom pain for some people:
Mirror box. This device contains mirrors that make it look like an amputated limb exists. The mirror box has two openings — one for the intact limb and one for the residual limb.
The person then performs symmetrical exercises, while watching the intact limb move and imagining that he or she is actually observing the missing limb moving. Some studies, though not all, have found that this exercise may help relieve phantom pain.
Acupuncture. The National Institutes of Health has found that acupuncture may ease some types of chronic pain. In acupuncture, the practitioner inserts extremely fine, sterilized stainless steel needles into the skin at specific points on the body. Acupuncture is generally considered safe when performed correctly.
Repetitive transcranial magnetic stimulation (rTMS). This therapy uses an electromagnetic coil placed against the forehead. Short pulses are sent through the coil that cause small electrical currents in the nerves located in a specifically targeted area of the brain.
Research suggests that this therapy may be helpful for phantom pain, though it isn’t yet specifically approved for this condition. The magnetic field is similar to the one used in MRI scans. Side effects may include a mild headache or lightheadedness.
Spinal cord stimulation. Your doctor inserts tiny electrodes along your spinal cord. A small electrical current delivered continuously to the spinal cord can sometimes relieve pain.
Surgery may be an option if other treatments haven’t helped. Surgical options include:
Brain stimulation. Deep brain stimulation and motor cortex stimulation are similar to spinal cord stimulation except that the current is delivered within the brain. A surgeon uses a magnetic resonance imaging (MRI) scan to position the electrodes correctly. Although the data are still limited and these treatments aren’t specifically approved for phantom pain, brain stimulation appears to be a promising option in selected individuals.
Stump revision or neurectomy. If the pain is from nerve irritation in the stump, surgery can sometimes be helpful. But, cutting the nerves includes a risk of making the pain worse.
Potential future treatment
Newer approaches to relieve phantom pain include virtual reality goggles. The computer program for the goggles mirrors the person’s intact limb, so it looks like there’s been no amputation. The person then moves his or her virtual limb around to accomplish various tasks, such as batting away a ball hanging in midair.
Although this technique has been tested only on a small number of people, it appears to help relieve phantom pain.
Can you prevent phantom limb pain?
Some studies suggest that using spinal and general anesthesia together during limb amputation surgery may lower the risk of phantom limb pain.