What is Phantom Limb Pain?
Every year, between 30,000 to 40,000 people in the United States have a limb amputated. There are many reasons for this, such as severe injuries, tumors, blood vessel diseases, and infections. After an amputation, it’s not uncommon for people to experience pain. There are two main types of pain that are common: residual limb pain (RLP) and phantom limb pain (PLP).
Phantom limb pain is when someone feels pain in a limb that’s no longer there. This type of pain often affects people who’ve had a limb amputated, but the exact cause of this kind of pain isn’t fully understood. PLP can have a range of symptoms and vary in severity. It’s important to understand that PLP is different than other conditions, like RLP.
Residual limb pain, also known as “stump pain,” is pain that someone feels at the site of the amputation. This type of pain tends to be most common right after the amputation has taken place and usually gets better as the wound heals. Unlike PLP, RLP is often a sign of an underlying issue like a trapped nerve, growths of nerve tissue, surgical trauma, decreased blood flow, skin breaking down, or infections. It’s worth noting that more than half of the people who have PLP also experience RLP. Both types of pain can happen at the same time, but it’s important to tell the difference since they have different causes and treatments.
Dealing with PLP and RLP is a significant challenge in medicine both in terms of understanding how many people it affects and in terms of finding effective treatments. Almost all people who’ve had an amputation experience some form of pain related to their amputation. About 79.9% of people report PLP and 67.7% report RLP. These types of pain can greatly lower a person’s quality of life and can sometimes be very difficult to manage.
What Causes Phantom Limb Pain?
The exact cause of Phantom Limb Pain (PLP), a type of pain that feels like it’s coming from a body part that’s no longer there, isn’t fully understood yet. Different theories have been suggested, and most people agree that there are likely many factors involved. It was believed for many years that the pain was caused by the irritation of nerve endings that had been cut during amputation. This belief was backed up by the fact that almost all people who have had an amputation develop neuromas, or nerve growths, in the remaining part of the limb.
However, over the past few decades, new technology for taking pictures of the brain, like MRI and PET scans, has shown that the brain may also play a role in phantom pain. These scans showed activity in the parts of the brain that were connected to the amputated limb when the patient experienced phantom pain. Given these findings, it’s now believed that phantom pain likely involves a combination of factors related to both the peripheral nervous system, which includes nerves outside the brain and spinal cord, and the central nervous system, which includes the brain and spinal cord.
Risk Factors and Frequency for Phantom Limb Pain
In 2005, one in every 190 people in the U.S. were living with limb loss, totaling up to 1.6 million people. This number is projected to increase to 3.6 million by 2050. Among those who have had a limb amputated, 60% to 85% experience phantom limb pain (PLP).
The common reasons for limb loss include:
- Vascular disorders (the most common)
- Injuries
- Cancer
- Conditions present at birth
Signs and Symptoms of Phantom Limb Pain
Phantom limb pain (PLP) is often described by patients as a sensation of tingling, throbbing, or sharp pains, like pins and needles, in a limb that has been amputated and is no longer there. It’s usually more common in people who’ve had an arm amputated, compared to a leg. The pain can come and go, and its severity can range from mild to severe. This can start right after the amputation, or even years later. It’s important to distinguish PLP from residual limb pain (RLP).
The goal of a physical exam is to rule out the causes of RLP. The first step is to carefully check the skin for signs of wounds or infection. Next, the person’s sense of touch should be tested, and the doctor will check for extreme sensitivity to touch (allodynia) and heightened pain responses (hyperalgesia). Additionally, the joint above where the limb was amputated needs to be checked for dysfunction.
With RLP, the pain intensity is usually not severe, and the sensations felt can be described as:
- Pressing
- Throbbing
- Burning
- Squeezing
- Stabbing
Testing for Phantom Limb Pain
The diagnosis of Phantom Limb Pain (PLP), a condition where you feel pain in a limb that isn’t actually there, is primarily based on the patient’s own experiences and history. This means lab tests aren’t typically needed. However, to rule out other possible conditions like infections, a Complete Blood Count (CBC) test, which evaluates your overall health and detects a wide range of disorders, might be recommended.
An ultrasound, which uses high-frequency sound waves to capture live images from inside your body, can also be requested. This will allow the doctor to check for neuromas, which are abnormal growth of nerve tissue, and might be causing the pain.
Lastly, if you’re experiencing outside factors that seem to be contributing to your pain, a psychological evaluation may be suggested. This type of evaluation can help find ways to cope and deal with these triggers.
Treatment Options for Phantom Limb Pain
Unfortunately, treating phantom limb pain (PLP – a feeling of discomfort in a limb that has been amputated) isn’t always successful. While pain linked to the remaining part of the limb (RLP) might be related to a physical cause that can be addressed, phantom limb pain is often focused on managing the symptoms.
Various medications are used to treat PLP. These include:
- Over-the-counter painkillers, like ibuprofen or acetaminophen, which are the most common treatment for PLP.
- Opioids, a type of strong painkiller, such as tapentadol, are sometimes used to treat nerve pain and PLP. These should be used together with other medications like antidepressants or nerve modulation medicines such as gabapentin or pregabalin. Due to the potential for developing a tolerance or dependence, caution is needed when using opioids for non-life-threatening conditions.
- Antidepressants can help manage PLP. Amitriptyline is often used, but other types like nortriptyline and desipramine could be equally effective. Duloxetine is another antidepressant that has shown promising results.
- Anticonvulsants (medications typically used to treat seizures), like gabapentin and pregabalin, have shown mixed results in treating PLP.
- N-methyl-d-aspartate (NMDA) receptor antagonists, such as ketamine and dextromethorphan, have shown effectiveness in treating pain syndromes, although they work in a way we don’t fully understand yet. Another NMDA receptor antagonist, Memantine, showed mixed results..
- Beta-blockers (propranolol) and calcium channel blockers (nifedipine) have unclear data regarding their effectiveness against PLP.
- Topical Analgesics. These are painkillers you put on your skin. Capsaicin has been shown in some small studies to reduce sensitivity and PLP, but more research is needed.
- Botulinum toxin type B injections. These are used to treat excessive sweating in patients after amputation. This excessive sweating can interfere with the use of a prosthetic limb and can also affect both phantom limb and RLP. In some small studies, these injections have been shown to reduce RLP, PLP, and sweating.
- Local anesthetics. Some studies have examined the effectiveness of local anesthetics in treating PLP, with mixed results.
Non-drug treatments for PLP include:
- Transcutaneous electrical nerve stimulation (TENS). This uses a low-voltage electric current to manage pain. It’s thought to be most effective for PLP when used at a low frequency and high intensity and can also help relieve RLP.
- Mirror therapy. This therapy uses a mirror to create a reflective illusion of the affected limb, which can help reduce feelings of pain. Some small studies have found mirror therapy to be beneficial for PLP.
- Biofeedback, which helps you become more aware of your body’s responses and learn to control them.
- Acupuncture. Research into the effectiveness of acupuncture for PLP is ongoing.
- Spinal cord stimulation (SCS). This involves an implantable device that stimulates nerve pathways within the spinal cord. This can often be an effective therapy for managing PLP.
- Other nerve stimulation techniques, such as peripheral nerve stimulation (PNS), can be helpful for both PLP and RLP.
- Virtual and Augmented Reality technologies. These advanced forms of “mirror therapy” program the movements of the remaining limb part into virtual or augmented reality headsets to replicate the movements of a ‘whole’ limb in a virtual world. This treatment has shown to be effective in a few case studies, but larger studies are needed to confirm its effectiveness.
A procedure that changes the circulation of blood to a particular region (sympathetic block) might also help with PLP. In some cases, additional surgeries on the remaining part of the limb might be needed.
What else can Phantom Limb Pain be?
Some conditions that can be confused because they have similar symptoms include:
- Infection in a joint (Septic arthritis)
- Infection in the bone (Osteomyelitis)
- Body’s reaction to a foreign substance (Foreign body reaction)
- Growth of nerve tissue (Neuroma)
- Inflammation in the joint (Arthritis)
