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Health and Disease

Phantom Limb: Perceiving the Invisible

By Swetha Babu

Published 3:02 PM EST, Sat July 10, 2021

Introduction

The incidence of phantom limb is reported to be as high as 60-80% in patients post-amputation. Phantom limb pain should be differentiated from residual limb pain (RLP), as the latter originates from the actual site of the amputation.

Unlike phantom limb, RLP is often a manifestation of an underlying source, such as nerve entrapment, skin infections, surgical trauma, etc.

Onset and Symptoms

The onset of phantom limb mostly occurs immediately after amputation, however, some are documented to onset after a few weeks, although, rarely months later. The rise towards maximal sensation and pain differs between patients, often due to the contrasting extent of trauma and amputation.

Phantom pains are often described as crushing, burning, tingling, and cramping. Phantom sensations can be categorised into three different types:

–   Kinetic (movement)

–   Kinaesthetic (position and shape)

–   Exteroceptive (other stimuli such as touch, temperature and irritations)

 Image 1

Pathophysiology Theories behind phantom pain

Peripheral Nerve Changes

Amputation can result in a great trauma to nerves and tissues surrounding the site of amputation. 

This damage disrupts the normal nervous signals involved with the missing limb. The proximal portions of severed nerves begin to form neuromas (benign growths of nerve tissue), and the nerves become hyper-excitable, resulting in spontaneous discharges of impulses – pain and other sensations are experienced. 

Brain Changes

There has been significant research into cortical reorganisation, and it is a commonly cited factor in phantom limb pain. Cortical reorganisation refers to how the brain ‘re-maps’ the sections of the brain, adapting to significant stimuli. This can result in stimulation of nerves in the residual limb and the surrounding areas, causing the experience of pain and sensation in the missing limb. There is also a correlation between the extent of cortical reorganisation and the amount of pain that the patient experiences. 

An example of Cortical Reorganisation in response to amputation:

Psychological Factors

Sensations and pain could be influenced by memory of the incident, memory of pain proceeding the amputation, mood state, and a variety of other social concerns. In addition, circulating epinephrine within the body resulting from emotional distress can contribute to the stimulations of the peripheral nervous system, which can develop into the perception of sensations and pain in the amputated section of the limb. 

Evaluating Symptoms

The diagnosis of this phantom limb phenomenon is primarily a diagnosis of exclusion and is greatly dependent on the patient’s history, hence laboratory tests are less required.  A complete blood count (CBC) can help rule out infection as the source of paraesthesia. An ultrasound can be ordered to look for neuromas as a possible pain stimulator. However, most importantly, a psychology evaluation may be indicative if the patient is having significant extrinsic triggers that may be contributing to the patient’s pain, which could signify the requirement of psychiatric therapy.

Treatment and Prognosis

Often, when phantom limb pain and sensations continue vigorously for more than six months, the prognosis for spontaneous improvement is poor: some patients will experience a lifelong struggle with chronic pain. Phantom limb is a very difficult and complex condition to treat, particularly due to the lack of understanding of the nature of the condition, and that the cause of the phenomenon varies between patients.

The first treatment is usually conservative and should include non-pharmacological and nonsurgical methods. Prosthetists should assess the stump – the site of amputation – and should encourage the patient to use a prosthetic device for improved mobility. Psychotherapists may help identify the psychological cause of the pain and sensations experienced by the patient with the aim to mitigate the experiences and to ease anxiety and depression. In the event that neither solution is successful, pharmacists will work to select appropriate pharmacological agents. The medication should be specific to the extent of pain and/or sensations, considering its debilitation and hindrance on everyday life, as well as the history of symptoms. The patient must be aware of why the medication is being administered and educated on the different pharmacological agents available and their effectiveness and adverse effects.

Treating phantom limbs tends to be for symptomatic control, and although no medications specifically for phantom limbs exist, some drugs designed to treat other conditions have been helpful in relieving nerve pain: 

  • Antidepressants, especially Tricyclic antidepressants, help relieve the pain of phantom limb phenomena. 
  • Receptor antagonist medications, specifically NMDA receptor antagonists, are anaesthetics which bind to specific receptors on nerve cells, blocking the binding of a protein called glutamate, which has a crucial role in relaying nerve signals.

Conclusion

Research about phantom limbs is still in early stages, hence currently nothing more can be done to prevent, reduce, and cure phantom limbs. With a variety of psychotherapy options, medication, and prosthetics, alongside occupational therapy, phantom limb pain and sensations can be relieved in some, but not all, cases. As mentioned before, there is no one treatment that works reliably or consistently in all patients; the outcomes for most patients are limited and the quality of life can be poor.

Swetha Babu, Youth Medical Journal 2021

References

BJA Education. (2016) 16(3): 107–112. Pain after amputation. https://doi.org/10.1093/bjaed/mkv028

Image 1: https://medicalxpress.com/news/2018-09-theory-phantom-limb-pain-effective. html

Hanya-Deutmeter, A., Cascella, A., Varacallo, A. (2021). Phantom Limb Pain. National Centre for Biotechnology Information. https://www.ncbi.nlm.nih.gov/books/NBK448188/

Mayo Clinic, Mayo Foundation for Medical Education and Research. (2020, Oct. 29) Phantom Pain. https://www.mayoclinic.org/diseases-conditions/phantom-pain/diagnosis-treatment/drc-20376278

Cleveland Clinic. (2016, Mar. 14). Phantom Limb Pain. https://my.clevelandclinic.org/health/diseases/12092-phantom-limb-pain