Phantom pain: pinching in nowhere

22. November 2011
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Whether from a car accident or adult-onset diabetes: the number of amputations is rising. Whatever is not there should also actually not cause any more pain: not so at all! Patients with phantom pain are, according to many physicians, quite a headache.

Previously dismissed as a purely psychological phenomenon, researchers have now gained new insights: processes in the brain and spinal cord are responsible for the pain in absent limbs. And quite often: in Germany the number of amputations is well over 50,000 per year, for the United States approximately 200,000 such OPs are indicated. Arms or legs are mostly affected, but hardly a body part can be excluded from phantom pain.

It’s gone – but it hurts!

As Europe’s largest survey showed, three out of four patients suffer after an arm or leg amputation from phantom pain. The study involved some 537 patients, of whom only fifteen percent had no such ailments. Those afflicted describe sensations that can be as mild as tingling, temperature stimuli or phenomena, as if the – inexistent – leg feels heavy after long walks. The spectrum of feelings described also include those as severe as cramps and stabbing pains. These sensations have also been observed much more frequently where the limb before amputation had already caused complaints for years. Amazingly for the authors: about 62 percent in addition suffered from sleep disturbances. “Because lack of sleep in turn reinforces the perception of pain and, due to fatigue, prostheses are used less, this is something that has to be kept in mind,” stipulates Dr. Uwe Kern from the Pain and Palliative Care Center in Wiesbaden. Yet exactly how phantom pain occurs neurologists still cannot explain in an encompassing way.

Molecular discomfort

Today, researchers describe a number of processes that are relevant in phantom pain: At the end of the amputation-stump, neuromes – particular growths of nerve endings – are formed. These get tangled together in their growth and irritate one another. This alone however cannot be the cause, because patients who are already born with missing limbs – one thinks of thalidomide victims – report similar symptoms. “With phantom pain, the brain compensates incorrectly for the lack of signal from an amputated body part via the production of pain,” explains Professor Dr. Christoph Maier from BG University Hospital Bergmannsheil, Bochum. “The cause of this includes nerve cells, which are virtually made redundant by the amputation,” adds Professor Thomas Weiss of the University of Jena, Department of Biological and Clinical Psychology. Pain-processing structures change and shifting of neuronal functions in the brain takes place.

Other explanations given are also based on processes in the rear area of the spinal cord: so-called C-fibres, which are specialised nerve fibres that transmit stimuli, die off. Neural impulses, which are usually of no significance, are suddenly over-interpreted as pain. This outcome is amplified by activation of neuromas. However metabolic processes also get out of control. Nerve fibres produce more substance P, a protein. This process also reinforces stimuli that are usually lost in background noise, making them reach the point of pain.

First plan then amputate

“Phantom pain is very difficult to treat,” says Weiss. Good planning for the amputative surgical procedure can nevertheless prevent this pain for some patients or at least reduce the associated distress, as shown by various studies. It starts with most peripheral separation possible, followed by optimal conditions in the amputation stump: the shortened nerve-ends being well separated from the stump-ending; stable fixed muscles as well as a careful dissection of the soft tissues do have a positive effect. Subsequent to that, much less impact can be made. Studies show particularly that surgical post-amputative corrections, but also techniques of neurostimulation and local anaesthetic methods, do not offer anything more than does a placebo.

Drugs – before or afterwards?

Pharmacological efforts have been undertaken, which are primarily based on knowledge gained in treatment of neuropathic pain. British scientists are now investigating, as part of a literature review, whether preventive doses of analgesics could perhaps offer something. A total of eleven studies came into the picture, among others those of local anaesthetics, opioids, N-methyl-D-aspartate receptor antagonists or gamma-aminobutyric acid analogues, administered either alone or in combinations. The sobering conclusion: “There is no reliable data on the use of preventive analgesia used in order to minimise the risk of chronic pain after amputation,” the authors write. Nevertheless, the substances may help postoperatively, as analgesics fit into the WHO pain relief ladder. In addition, antidepressants, anticonvulsants, antipsychotics, and muscle relaxants are employed. Pain therapists suggest a potential strategy that begins in the short term with the peptide hormone calcitonin (up to three days), possibly supplemented by analgesics. If the effect is not sufficient, antidepressants, anticonvulsants and physical measures follow. If these strategies also show no effect, referral to specialists is inevitable.

Prosthesis on, away with pain

Pain researchers at the University of Jena have gone a different route. They’ve developed special prostheses for hand or forearm which are connected through a sleeve with the upper arm amputation-stump. The original plan was to have the pressure sensors only control grip strength in the fingers. “Our system will now also transfer this sensory information from the hand to the arm,” says Professor Gunther Hofmann, Director of the Department of Trauma, Hand and Reconstructive Surgery at the University of Jena. The prosthesis gives the body therefore a response as if it were its own hand. This has consequences: restructuring in the brain can be reversed, according to the researchers from Jena. In addition to this high-tech aspect, phenomena of perception also play a role: if the prosthesis is perceived as part of the body, phantom pains are also much less common.

Reflected away

Another method comes from the U.S. neurologist Vilayanur Ramachandran: already 15 years ago, he developed mirror therapy. In this, the patient sits at a table and sees the reflection of the remaining arm or leg. His or her brain is fooled: the amputated limb is still there and can also be controlled. Together with sensory stimuli or movements of the intact – and thus a mirror image of the amputee’s – arm or leg, it will be conveyed to the brain that everything is well. “The patient learns to control his phantom limb, through which the sensation of pain can be sigificantly reduced,” says Christopher Maier. Various methods are used here – sometimes exercises work better, sometimes instead sensation of touch. The good thing about the method: side effects are not to be feared. Here also, virtual reality has already moved in: researchers at the University of Manchester have developed sensors which are attached to the non-amputated limb. With a three-dimensional computer program and a head mounted display, the patient then sees as they move both limbs almost at once. In four out of five subjects improvements occurred, sometimes even at the first session.

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