Phantom Limb Pain (PLP) is a common problem in patients following an amputated extremity. PLP is the sensation of pain that a patient experiences in a limb following removal. It is estimated that 45-85% of amputees experience some degree of phantom limb sensation following amputation (Kuffler, 2018). Patients typically experience PLP in the first month following surgery and again at one-year post-op. Typically, this pain dissipates over time, but some patients continue to experience intense pain chronically. PLP affects patients physically and mentally and often inhibits rehabilitation. The cause of this neuropathic pain is not entirely understood. Some research has associated the presence of neuromas, which are growths of sensory nerve fibers, at the site of amputation (Ramachadran et al., 1998). These neuromas may form from nerve endings that are severed during the amputation. Prior research has led to the belief that some of the pain associated with PLP is due to the nerves continuing to produce action potentials (Ramachadran et al., 1998). However, other possible explanations have been made to describe the cause, including brain changes, dorsal horn changes, and epigenetics.
Presently, there is no standard treatment for PLP. Non-medication therapies are used, including mirror box therapy, with varying levels of success. A few treatments that healthcare professionals may trial for PLP patients include local anesthetics like lidocaine administered into the spinal canal, NSAIDs, antidepressants, anticonvulsants, and opioids (Kuffler, 2018). However, non-traditional treatment approaches have been studied too. Intriguingly, dextromethorphan, also known as Robitussin, has been used to treat PLP. Dextromethorphan is an N-methyl-D-aspartate (NMDAR) antagonist, which has been found to be successful in treating neuropathic pain, by preferentially binding to the NMDA receptor, which is a hypothesized mechanism of the pain. Another NMDAR antagonist is ketamine, which carries increased cognitive and CNS side effects. In a small 3-week study in 2002, PLP patients who received dextromethorphan experienced relief of PLP symptoms at doses of 120 and 180 mg, without significant side effects, compared to the control group (Abraham et al., 2002). Additionally, a study was performed in 2014, testing the efficacy of low-dose dextromethorphan on post-surgical pain in mice. It showed improved behavior and cognitive function in treatment of hyperalgesia following surgery (Morel et al., 2014). Despite the promising results in these small studies, there have been few studies to date testing the efficacy of dextromethorphan for the treatment of PLP. Dextromethorphan, when taken in therapeutic doses, is unique in that it may treat recurrent PLP without the risks associated with opioids or ketamine. However, further expansion of clinical studies is necessary to determine if dextromethorphan is an effective treatment for PLP.
Abraham, R., Marouani, N., Kollender, Y., Meller, I., & Weinbroum, A. A. (2002). Dextromethorphan for phantom pain attenuation in cancer amputees: A double-blind crossover trial involving three patients. The Clinical Journal of Pain, 18(5), 282–285. https://doi.org/10.1097/00002508-200209000-00002
Kuffler, D. P. (2018). Coping with Phantom Limb Pain. Molecular Neurobiology, 55(1), 70–84. https://doi.org/10.1007/s12035-017-0718-9
Morel, V., Pickering, G., Etienne, M., Dupuis, A., Privat, A.-M., Chalus, M., Eschalier, A., & Daulhac, L. (2014). Low doses of dextromethorphan have a beneficial effect in the treatment of neuropathic pain. Fundamental & Clinical Pharmacology, 28(6), 671–680. https://doi.org/10.1111/fcp.12076
Ramachandran, V. S., & Hirstein, W. (1998). The perception of phantom limbs. The D. O. Hebb lecture. Brain: A Journal of Neurology, 121 ( Pt 9), 1603–1630. https://doi.org/10.1093/brain/121.9.1603
Hi Austin! Its interesting how limited treatment options are for PLP given that it has been around since the mid-1500's (Martin, n.d.). In trying to find more research regarding mirror box therapy, I have had little success finding it being consistently beneficial or it even being recommended as first line treatment (Barban et al., 2016). But honestly is it so bad that Robitussin can be used as PLP treatment? It is so widely available over the counter and inexpensive as compared to trialing different pain medications that will, most likely, not relieve them of their perceived pain. All in all, this may be a good thing for those who have PLP but you are definitely right, further research should be conducted in order to support continuing treatment using Robitussin.
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Barbin, J., Seetha, V., Casillas, J. M., Paysant, J., & Pérennou, D. (2016). The effects of mirror therapy on pain and motor control of phantom limb in amputees: A systematic review. Annals of physical and rehabilitation medicine, 59(4), 270–275. https://doi.org/10.1016/j.rehab.2016.04.001
Martin, R. (n.d.). Why Do People Get Phantom Limb Syndrome?. Birmingham Hand and Plastic Surgery. Retrieved from https://birminghamhandandplasticsurgery.com/why-do-people-get-phantom-limb-syndrome/#:~:text=Later%2C%20the%20term%20%E2%80%9Cphantom%20limb%E2%80%9D%20was%20coined%20by,or%20feet%20could%20also%20go%20through%20the%20condition