Phantom Limb Pain

Shinjini Bandopadhyay, Amity University Kolkata

ORIGIN AND UNDERSTANDING OF PHANTOM LIMB PAIN

Phantom Limb Pain (PLP) is the pain associated with a missing or amputated limb. Severe trauma, tumor, vascular diseases, or infections can result in surgical removal or amputation of a limb, giving rise to phantom limb sensations of excruciating pain or discomfort in most patients, who report feeling like their amputated limb is still present. This intense pain experienced by amputees in their ‘phantom’ limb is known as PLP, and it can range from throbbing, stabbing, electric shock-like pain to cramping or painful, immobilized sensations. Many patients can also perform or control phantom movements such as wiggling toes or opening/closing their hand, immediately after surgery.

This phenomenon of phantom limb pain was first documented by a French surgeon in 1552, but it was not medically defined until the American Civil War. During the war, there was a sharp rise in reported cases of PLP, but it was dismissed as a psychological problem. Later during World War II, many wounded soldiers with severed or amputated limbs faced the additional fear of being stigmatized as mentally ill and concealed their struggles with PLP. 

Since the 16^th century, there has been extensive research and clinical progress in defining and treating PLP. However, the exact mechanism and underlying pathophysiology of phantom limb pain is still largely unknown and continues to perplex scientists and doctors. 

It became evident over recent decades that one of the major contributing factors for this phenomenon is neuroplasticity, which is the ability of neurons in the brain to change or modify their behaviour/function. Numerous theories are surrounding the neurological pathways that form the backbone of the manifestation of phantom limb complications; some of these theories hold the central nervous system (CNS) responsible for regulating PLP whereas the others also include the significance of the peripheral nervous system (PNS) in influencing PLP.

NEUROLOGICAL BASIS OF PHANTOM LIMB PAIN

The most popular CNS theory currently is cortical remapping theory (CRT) or cortical reorganization. This is a phenomenon that is also known as map expansion neuroplasticity, in which the brain is believed to respond to limb loss by reorganizing somatosensory maps. These are ‘maps’ present in regions of the brain’s cerebral cortex for handling the receptors present in specific organs or body parts, and their functioning is based on receiving sensations of touch, movement, pain, and temperature. The remarkable plasticity of the mammalian brain is accountable for somatosensory cortical rearrangement as a neurophysiological response to amputation—PLP can be explained by cortical ‘remapping’ where the neurons that once received input from an arm before its amputation, subsequently begin responding to new inputs from the face that invade the nearby arm-associated somatosensory region; as a result, with facial stimulation, a patient may experience phantom limb sensations, including pain. This is due to a sudden absence of sensory information reaching the cortical area that once controlled the missing limb. 

Recent research also focuses greatly on the peripheral causes of PLP, basing it on the inability of the severed nerves to repair previous connections and the role played by the dorsal root ganglion (DRG). When an injury occurs to the nerves, neurons in the DRG increase their nociceptive (pain) signalling through increases in neuronal excitability and the creation of ectopic discharges (which induce neuropathic pain). This aberrant signalling may produce PLP. However, peripheral factors alone cannot mediate PLP and the PNS is usually involved alongside the CNS. The dysregulated neural inputs caused by peripheral nerve injury cause excessive aberrant inputs that eventually create changes in the cortex. Furthermore, PNS pain modulation is generally maintained by the CNS and is affected by emotional state, memories, and attention (all controlled by CNS). Hence, while an amputation directly affects the PNS, the CNS is also affected due to change in sensory and movement signal pathways.  

TREATMENT AND THERAPY FOR PLP

The debilitating chronic pain caused due to PLP has been subjected to various treatment options. Phantom limb pain in some patients may gradually disappear over a few months to one year if left untreated, but some suffer from PLP for decades. Treatment regimens include pharmacotherapy, adjuvant therapy, and surgical intervention. A variety of medications such as analgesics, sedatives, anti-depressants, and anticonvulsants can help alleviate pain symptoms. Non-surgical approaches include shock therapy and acupuncture. Non-invasive treatment regimens may be useful when other methods fail, such as deep brain stimulation, intrathecal drug delivery systems, and spinal cord stimulation.

Adjuvant therapy includes transcutaneous nerve stimulation (TENS), mirror therapy, electroconvulsive therapy, acupuncture, and massage. 

Among these, mirror box therapy is a novel therapeutic method that has proved successful in a small number of patients. It is especially effective for patients suffering from ‘learned paralysis’ (experienced by those whose limbs were paralyzed before amputation or loss). In mirror therapy, the patient uses a box without a roof, with a mirror in the center, and two holes. One hole is used to insert the patient’s intact arm or leg and the other is reserved for ‘inserting’ their phantom limb. The patient watches the reflection of their existing limb in the mirror and this tricks the brain into visualizing the phantom limb. By continuously repeating this, the patient trains their brain into ‘moving’ the phantom limb and this eventually relieves them of PLP and often leads to long-term relief from learned paralysis and associated pain.

The study of PLP and the associated treatment methods are still being researched in great detail. The exact cause, manifestation, and therapeutic scope of PLP will help open avenues to improved understanding and interpretation of the brain and its regulation of pain. 

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REFERENCES

1. Collins KL, Russell HG, Schumacher PJ, Robinson-Freeman KE, O’Conor EC, Gibney KD, Yambem O, Dykes RW, Waters RS, Tsao JW.(2018). A review of current theories and treatments for phantom limb pain J Clin Invest.128(6).2168-2176  DOI: https://dx.doi.org/10.1172%2FJCI94003

2. Amreet Kaur, Yuxi Guan,(2018) Phantom limb pain: A literature review,Chinese Journal of Traumatology,Volume 21, Issue 6,2018,366-368,ISSN 1008-1275,DOI: https://dx.doi.org/10.1016%2Fj.cjtee.2018.04.006 

3. J. Barbin, V. Seetha, J.M. Casillas, J. Paysant, D. Pérennou,(2016)The effects of mirror therapy on pain and motor control of phantom limb in amputees: A systematic review, Annals of Physical and Rehabilitation Medicine,Volume 59, Issue 4, 270-275,ISSN 1877-0657,DOI: https://doi.org/10.1016/j.rehab.2016.04.001

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