What Does Phantom Pain/ Sensation Feel Like

What Does Phantom Pain/ Sensation Feel Like/Phantom Pain is clinically defined as the perception of pain or discomfort in a limb that no longer exists.  Although PLP most commonly presents as a pathological sequelae in amputee patients, the underlying pathophysiology remains poorly understood. PLP can present along a wide clinical spectrum and varying severity of symptoms.  The condition should be differentiated from other related but separate clinical conditions, including residual limb pain (RLP).  RLP (formerly known as “stump pain”) is pain that originates from the actual site of the amputated limb.  It is most common in the early post-amputation period and tends to resolve with wound healing. Unlike PLP, RLP is often a manifestation of an underlying source, such as nerve entrapment, neuroma formation, surgical trauma, ischemia, skin breakdown, or infection.[rx]

Phantom pain is a perception that an individual experiences relating to a limb or an organ that is not physically part of the body. Limb loss is a result of either removal by amputation or congenital limb deficiency.^[rx] However, phantom limb sensations can also occur following nerve avulsion or spinal cord injury.

Mechanisms Phantom Leg Syndrome

The mechanism responsible for PLP and PLS is still debatable, however a lot of theories had been given. Following amputation, there may be formation of neuroma showing abnormal spontaneous activity, and on mechanical and chemical stimulation, which is thought to be due to upregulation of sodium channels. Furthermore, other factors though to have an influence on the PLP are decreased threshold for PLP, increased c-fiber activity, inverse relationship between pressure pain threshold and phantom limb pain intensity, abnormal activity of dorsal root ganglion, and so on.[rx,rx] Sympathetic nervous system also plays a role in maintaining PLP.[rx,rx] Further, there is spinal plasticity, i.e., increase in the excitability of spinal neurons, more accessibility of Aδ- and c-fibers to other pathways.[rx] N-methyl-D-aspartate receptor systems are also believed to have a role in “wind-up” phenomenon seen in PLP.[rx] Furthermore, spinal and cerebral reorganization occurs and there is a relationship between degree of reorganization and pain.[rx,rx]

Types of Phantom Leg Syndrome

There are various types of sensations that may be felt:

• Sensations related to the phantom limb’s posture –  length and volume e.g. feeling that the phantom limb is behaving just like a normal limb like sitting with the knee bent or feeling that the phantom limb is as heavy as the other limb. Sometimes, an amputee will experience a sensation called telescoping. This is the feeling that the phantom limb is gradually shortening over time.
• Sensations of movement – (e.g. feeling that the phantom foot is moving).
• Sensations of touch, temperature – pressure and itchiness. Many amputees report of feeling heat, tingling, itchiness, and pain.

Causes of Phantom Leg Syndrome

• 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 spontaneous discharges. [rx]
• 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. [rx]
• Brain Changes – 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. [rx]
• Psychogenic Factors – 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. [rx] As with any other kind of pain, you may find that certain activities or conditions will trigger PLP. Some of these triggers might include-
• Touch
• Urination or defecation
• Sexual intercourse
• Angina
• Cigarette smoking
• Changes in barometric pressure
• Herpes zoster
• Exposure to cold.

Symptoms of Phantom Leg Syndrome

It onset within the first few days of amputation. Comes and goes or is continuous. Often affects the part of the limb farthest from the body, such as the foot of an amputated leg. May be described as shooting, stabbing, boring, squeezing, throbbing or burning. Sometimes feels as if the phantom part is forced into an uncomfortable position. May be triggered by pressure on the remaining part of the limb or emotional stress.^[rx]

• Onset within the first week after amputation, though it can be delayed by months or longer
• Pain that comes and goes or is continuous
• Symptoms affecting the part of the limb farthest from the body, such as the foot of an amputated leg
• Pain that may be described as shooting, stabbing, cramping, pins and needles, crushing, throbbing, or burning

Phantom limb sensation – is a nonpainful feeling or sensation in the body part that was amputated. Phantom sensations are more commonly reported than stump pain or phantom limb pain. The sensations feel like the limb felt before the amputation, and are related to the same sense of awareness that helps people distinguish “myself” from others. The sensations occur from the interaction of current sensory inputs from your limb, and the internal “models” of the body in the brain.

• Early on, the phantom limb resembles the limb shape prior to amputation. It may be perceived in a certain position, have feelings of warmth or cold, itching, or tingling.
• Following amputation, it is common to “forget” the limb is absent and to attempt to use it—a sensation that can result in a fall.
• It is also common for people who experienced amputation to feel as though the upper portion of the limb is missing, or has shrunk. This phenomenon, called telescoping, is caused by a change in the internal model of the body in the brain. It also can cause the sensation that the amputated part of the limb is floating, or has even moved up inside the stump.

Stump pain is common in the postoperative period. It is felt only in the remaining body part, or stump. Stump pain may be felt at the incision or deeper into the residual limb. This pain is often described as sharp, burning, stabbing, or “electric.” Stump pain, which normally fades as the surgical scar heals, can coexist with phantom limb pain.

Phantom limb pain is a painful or unpleasant sensation in the lost body part. Sensations can include:

• Tingling, burning, and cramping (the most common pain felt from amputation)
• Shooting, stabbing, boring, squeezing, or throbbing pain
• Pain just like that experienced at the time of the accident or serious injury
• A feeling like the phantom limb is in a forced and uncomfortable position

Since phantom pain is related to the brain and nervous system, it can also be experienced in the nonamputated part of the limb, in the opposite nonamputated limb, or even in the neck or back. Phantom limb pain usually affects the part of the limb farthest from the body. For example, lower-limb phantom pain will usually be experienced in the toes, heel, instep, or top of the foot. The pain may be continuous, or it may come and go during the day. In many cases it occurs randomly.

Phantom pain may be triggered by

• Pressure on the remaining part of the limb from objects such as clothing
• Emotional stress
• Forgetting the limb’s absence and attempting to use it
• A poorly fitting artificial limb
• Stump pain

Diagnosis of Phantom Leg Syndrome

There are no medical tests to diagnose phantom limb pain. Diagnosis is made based on your symptoms and the history of what occurred before the pain started. For example, was there illness, trauma, or surgery before the amputation? Reporting clearly and precisely what seems to trigger the phantom pain will help your physical therapist diagnose the problem. The physical therapist may have you complete questionnaires about your symptoms and functional difficulties to help clarify details of your problem and how it is affecting your daily life and activities. All other possible sources of your pain symptoms must be ruled out.

Your physical therapist will

• Perform a careful examination of the bone and soft tissues of your stump to identify possible skin breakdown, infection, or abnormal pressure on weight-bearing contact points.
• Gently tap on the stump to identify possible nerve injury or a neuroma (an overgrowth of nerves in the stump).
• Check the fit of your prosthetic limb. (It is common for the shape of your stump to change over time, affecting the prosthetic’s fit and comfort.)
• Check to make sure that you are using the correct stump socks, and that you are putting your prosthetic on properly.
• Explain how any of the above changes can cause skin breakdown and provoke pain problems.

Your physical therapist will work with your physician to determine the need for additional tests to rule out other conditions, such as poor circulation, and may refer you for X-rays to identify bone spurs or other abnormal bone formations.

Treatment of Phantom Leg Syndrome

Pharmacotherapy

• NSAIDs/Tylenol – are the most commonly used treatment for phantom limb pain. The mechanism of action is unknown.[rx]
• Opioids – Randomized controlled trials have demonstrated the effectiveness of opioids for neuropathic pain and phantom limb pain. Drugs such as codeine and morphine may ease phantom limb pain for some people, but not everyone. Tell your doctor if you have a history of substance abuse before you take one of these drugs. Should be used in conjunction with antidepressants or neural modulating agents (i.e., gabapentin, pregabalin). [rx]
• Antidepressants – are commonly used for phantom limb pain. Amitryptiline, in particular, is the TCA of choice as it has shown good results, but other studies looking at Nortryptyline and desipramine have shown them to be equally effective. Duloxetine is another medication that has been showing some positive results. [rx]
• Anticonvulsants (Gabapentin, Pregabalin) – have shown mixed results. [rx] These drugs treat seizures, but some can also help with nerve pain. Examples include carbamazepine (Carbatrol, Epitol, Tegretol), gabapentin(Gralise, Neurontin), and pregabalin (Lyrica).
• Calcitonin  – The mechanism of action of calcitonin in treatment of PLP is not clear. Studies relative to its therapeutic role have been mixed [rx, rx].
• NMDA Receptor antagonist–  mechanism is not clear. Memantine has had mixed results.
• Beta-blockers (propranolol) – and calcium channel blocker (nifedipine) show unclear data. A sympathetic block may also help.
• Botulinum toxin type B injections – have been used to treat hyperhidrosis (excessive sweating) in the post-amputation patient.  Hyperhidrosis can not only hinder the use of a prosthetic but can adversely affect the course of phantom limb and residual limb pain. Treatment of the hyperhidrosis with botulinum toxin type B injections has shown in several small studies to reduce residual limb pain, phantom limb pain, and sweating. [rx]  Botulinum toxin type A is also being investigated, but so far has not been shown to decrease pain intensity compared to lidocaine/methylprednisolone. [rx]
• Capsaicin – have been shown in some small studies to reduce hypersensitivity and phantom limb pain, but the evidence is still weak and requires more investigation. [rx][rx]
• Tricyclic antidepressants – Drugs such as amitriptyline (Elavil), nortriptyline(Pamelor), and tramadol (Conzip, Ultram) can ease nerve pain by changing chemicals in your body that send pain signals.
• Biofeedback, Integrative, and Behavioral Methods – Although there are earlier reports suggesting temperature biofeedback to be helpful for burning sensation of PLP, there is no specific evidence to match specific types of PLP with specific biofeedback techniques [rx]. There is also a case report of visual feedback helpful in reduction of phantom pain [rx].

Other painkillers – A few other types may help with phantom limb pain, including:

• NMDA receptor antagonists, such asketamine and dextromethorphan
• Over-the-counter medicine, such as aspirin and acetaminophen
• A shot of a pain-blocking drug in the area where you got the amputation

References

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