Case of the Month #39: Post Amputation Pain by Dr Fiona Sweeney

Ms A was managed with ongoing morphine PCA for her mixed stump pain, opioid hyperalgesia and phantom limb pain. This was for a further 2 days on a weaning schedule with regular oramorph, paracetamol and ibuprofen. She was discharged with oramorph and pregabalin with close GP and outpatient pain services follow-up. Several different treatment approaches have been used to reduce phantom limb pain:

• surgical
• pharmacological
• physical therapy and prosthetics
• psychological interventions

Pharmacological

Multi-modal analgesia acts independently and synchronously on pain mechanisms at the varying loci points on the pain pathway (peripheral, spinal and cortical) as well as to reduce inter-individual variations⁴. Multi-modal analgesia can therefore target nociceptive and neuropathic pain at the site of the trauma, at the peripheral nerve, the dorsal horn, the descending pathway and at the brain to prevent sensitisation.

Perineural blockade:
A prospective study of 71 patients given a perineural infusion of a high concentration local anaesthetic infusion for 30 days (median duration) showed an incidence of only 3% of severe to intolerable phantom limb pain⁶.
Expert opinion supports the use of perineural catheters for 80hrs for the prevention of phantom limb syndrome^1,4.

Strong opioids:
Use is confined to managing wound pain and have been shown to have a very limited role in the management of phantom limb pain^1-6.

Novel analgesic agents:
Salmon calcitonin (100IU OD) is a neuropetptide postulated to act via altered beta-endorphin production, inhibition of prostaglandin and cytokine production and modulation of central serotonergic pathways. Small studies have shown that benefits on phantom limb pain were evident on follow-up a year later¹. Its use is not routine however^1-6.
Memantine is an NMDA antagonist that is relatively free of the psychotropic effects that limit ketamine, which can be given perineurally and orally. Evidence for its efficacy is expert opinion and not from trials¹. Ketamine has not been shown to prevent the development of phantom limb pain^1-6.

Gabapentinoids:
These drugs work via the alpha-2-delta subunit of the voltage dependent calcium channels and GABAB receptors in the CNS. There is again mixed trial evidence for prevention of phantom limb pain, but their use is more established in preventing chronic post-surgical pain with their anti-nociceptive, anti-neuropathic effect, opioid sparing effects¹.
 

Non-drug treatments

• Mirror therapy

Neuronal plasticity and reorganization of the somatosensory cortex is a process by which neighbouring regions of the area that represents the lost limb expand along the cortical map. This co-activates neurons formerly receiving and processing input from this limb and there is expansion of neuronal fields. Therapy thereby focusing on limb perception eg mirror therapy and virtual reality could prevent, reduce and even reverse these changes in cortical reorganization. Computational models have shown both the reorganisation and level of cortical activity to be important and work is ongoing to deduce whether it is predominantly the maladaptation of inter-regional functional connectivity or re-organisation that drives phantom limb pain and various types of modification of input into the affected brain might alter pain sensation.

• Acupuncture

• TENS and Sensory Discrimination training

Electrodes placed over the amputation stump in a region where stimulation excited the nerve that supplied the amputated portion of the arm has provided therapeutic benefit. Patients have to discriminate the frequency and location of the stimulation during a training period. Transcutaneous or transcranial direct current stimulation have shown therapeutic benefit during stimulation periods, but no longer lasting effects.

• Psychological interventions

Affective burden eg depression is not linked to occurrence of phantom limb pain, but can alter the course and severity of the pain. Cognitive behavioural therapy, trauma focused or eye movement desensitisation and reprocessing therapy have shown to be effective, although there are very few randomised controlled trials of small case numbers¹.

• Prosthetic Supply and Bionic Reconstruction