Phantom Limb Pain

Author: Dr. Karthik. K

The term “Phantom Limb” was first coined by Silas Weir Mitchell, a civil war surgeon, in Nineteenth Century.[1] It refers to a condition where a person feels sensation in the limb which has been amputated and does not exist. It may or may not be associated with pain, sometimes in combination with tingling or paraesthesia. When the patient complains of pain, it is termed as “Phantom Limb Pain”. It is often confused with “Stump Pain” where the pain is localized only to the stump of the amputated limb. Even though Mitchell was the first person to use the term Phantom limb in 1872, the description of post-amputation sensation was given way back in the 16th century by a French military surgeon, Ambroise Pare,[2] who gave several theories to explain this concept. But to date, still, the reason for this post-amputation sensation/pain remains unclear.

The widely accepted concept is that the cut end of the nerves develops neuromas following amputation which exhibits increased and abnormal activity on mechanical or chemical stimulation resulting in severe pain.[3] This peripheral mechanism theory became controversial, as injecting a local anesthetic agent to these neuromas or surgically removing these neuromas failed to abolish pain or sensation in the phantom limb. This lead to the development of some centralized mechanism theories. Neuroplasticity and Sensitization of spinal pain transmission neurons are believed to manifest as the expansion of peripheral respective amputated fields and mechanical hyperalgesia.[4] Cerebral reorganization[5] with changes at the subcortical level are noted in patients with phantom limb syndrome and are believed to play an important role. Further, the Sympathetic nervous system[6] also contributes to phantom limb pain. Few other theories too exist but none is found to be conclusive. Phantom limb Pain may be due to the contribution from several mechanisms and changes at several levels including peripheral, central, and psychological.

Although nearly 80-100% of patients feel the presence of a limb after amputation, 60-80% of these patients end up with pain in this absent limb in the early postoperative period, and up to 70% of them suffer pain up to 25 years after amputation.[7] These are the patients who are in need of medical attention. Over years after amputation, Phantom limb sensation fades or decreases in most patients. But around 30% of patients end up with Telescoping. Telescoping[8] refers to the condition which before the entire phantom arm fades, patients have the sensation of forearm shortening gradually ending up with only sensation of hand originating from the stump and later the only thumb. This is because the hand is represented in a comparatively larger area in the somatosensory cortex.[9]

          The most important risk factor associated with phantom limb pain is the presence of pre-amputation pain.[10] The duration of pre-amputation pain influences the duration of phantom limb pain. Phantom limb pain is seen more commonly with traumatic amputation rather than with surgical amputation.[9] Amputation earlier in childhood is associated with a lesser incidence of Phantom limb pain and increases with an increase in age.[7] Other risk facts include amputation of the upper limb, genetic predisposition, residual pain in the remaining limb, and female sex.

          A wide range of pharmacological, non-pharmacological, and surgical treatments are proposed and followed for Phantom limb pain. But none have been proven to be effective and satisfactory. Tricyclic Antidepressants and Sodium Channel blockers which are commonly used in the treatment of other neurogenic pain are often used in the treatment of Phantom limb pain.[11] Other pharmacological agents used includes NMDA antagonist, GABA agonists, Calcitonin, Beta-blockers, and opioids. Preemptive analgesics and the use of regional anesthesia in the perioperative are believed to help in the prevention of Phantom limb pain to some extent. Several surgical procedures including neurectomy, revision amputation, rhizotomy, sympathectomy have been done in an attempt to treat phantom limb pain. But none of them have been proven to be beneficial. Spinal cord stimulation is found to effective in a case report conducted in a group of patients who failed to respond to medical management.[12] Case reports of deep brain stimulation of thalamic nuclei and periventricular grey matter resulting in improvement of phantom limb pain have also been published.

          Non-pharmacological and psychological treatment plays a major part in treating phantom limb pain compared to medical and surgical management. They include Transcutaneous electrical nerve stimulation (TENS), Physiotherapy, Electroconvulsive therapy, acupuncture, biofeedback, prosthesis training, sensory discrimination therapy. Among all, Mirror therapy is found to be very effective. It is based on the principle of superimposing the intact limb as a mirrored image over the missing limb. The movement of the intact limb in the mirror creates a visual illusion of painless movement in the absent limb tricking the brain to perceive the absent limb as present and breaking the sensory pain pathway.

          To conclude the pathophysiology and treatment modalities of phantom limb sensation and pain still remain unclear and ineffective. Further, there is a lack of preventive measures. So, all the patients who need to undergo amputation should be well informed about this phenomenon and prepare the patient to handle this mentally.

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Bibliography:

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