Monday, February 26, 2007

Deep Brain Stimulation For Phantom Limb Pain

A clinical study of deep brain stimulation for the treatment of phantom limb pain (Bittar et al., 2005) reviews not only the treatments and mechanisms of phantom limb pain, but the historical aspects as well:
The 16th century French military surgeon Ambroise Pare was the first to medically document the phenomena of phantom limb sensation and phantom limb pain in 1551:

"For the patients, long after the amputation is made, say they still feel pain in the amputated part. Of this they complain strongly, a thing worthy and almost incredible to people who have not experienced this"

In 1830, the neurologist Charles Bell published a description of the condition in The Nervous System of the Human Body. The term ‘phantom’, however, is often credited to the American military surgeon Silas Weir Mitchell, who in 1871 gave the first modern description of a post-surgical ‘ghost’ occurring in an amputee:

"There is something almost tragical, something ghastly, in the notion of these thousands of spirit limbs haunting as many good soldiers, and every now and then tormenting them... when... the keen sense of the limb’s presence betrays the man into some effort, the failure of which of a sudden reminds him of his loss"
Bittar RG, Otero S, Carter H, Aziz TZ. (2005). Deep brain stimulation for phantom limb pain. J Clin Neurosci. 12: 399-404.

Phantom limb pain is an often severe and debilitating phenomenon that has been reported in up to 85% of amputees. Its pathophysiology is poorly understood. Peripheral and spinal mechanisms are thought to play a role in pain modulation in affected individuals; however central mechanisms are also likely to be of importance. The neuromatrix theory postulates a genetically determined representation of body image, which is modified by sensory input to create a neurosignature. Persistence of the neurosignature may be responsible for painless phantom limb sensations, whereas phantom limb pain may be due to abnormal reorganisation within the neuromatrix. This study assessed the clinical outcome of deep brain stimulation of the periventricular grey matter and somatosensory thalamus for the relief of chronic neuropathic pain associated with phantom limb in three patients. These patients were assessed preoperatively and at 3 month intervals postoperatively. Self-rated visual analogue scale pain scores assessed pain intensity, and the McGill Pain Questionnaire assessed the quality of the pain. Quality of life was assessed using the EUROQOL EQ-5D scale. Periventricular gray stimulation alone was optimal in two patients, whilst a combination of periventricular gray and thalamic stimulation produced the greatest degree of relief in one patient. At follow-up (mean 13.3 months) the intensity of pain was reduced by 62% (range 55-70%). In all three patients, the burning component of the pain was completely alleviated. Opiate intake was reduced in the two patients requiring morphine sulphate pre-operatively. Quality of life measures indicated a statistically significant improvement. This data supports the role for deep brain stimulation in patients with phantom limb pain. The medical literature relating to the epidemiology, pathogenesis, and treatment of this clinical entity is reviewed in detail.

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At February 27, 2007 10:55 AM, Blogger nullability said...

There was also a paper in the latest NeuroReport that uses magnetoencephalography to look more closely at the possible mechanisms by which deep brain stimulation affects pain. There was a very compelling case report of a man who experienced a dramatic increase in subjective pain when his implant was switched off.

Kringelbach, Morten L. et al. (2007). "Deep brain stimulation for chronic pain investigated with magnetoencephalography". Neuroreport, 18(3), pp. 223-228.


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