Re: Neuropathic pain: mechanisms and their clinical implications
Cohen and Mao  have described mechanisms and clinical implications of neuropathic pain. They also provided rationale for mechanism-based treatment separating neuropathic pain from nociceptive pain. However, the explosion of literature on neuropathic pain with extensive diagnosis and treatment modalities is a major concern. A major issue remains the lack of a gold standard and changing definition of neuropathic pain. The International Association for the Study of Pain (IASP), with extension by various other groups, provided an earlier definition of neuropathic pain. Further, it is likely true that many practicing physicians continue to accept the definition of neuropathic pain as the pain caused by injuries producing lesions in the somatosensory pathway in the peripheral or central nervous system . However, the definition of neuropathic pain was revised in 2008 by the Neuropathic Pain Special Interest Group (NeuPSIG) of the International Association for the Study of Pain as pain arising as a direct consequence of a lesion or disease affecting the somatosensory system . This new definition is proposed to ensure that neuropathic pain is distinguished from pain due to secondary changes in the nociceptive system as a result of the inherent plasticity in response to strong nociceptive stimulation and to ensure that neuropathic pain is distinguished from musculoskeletal pain and other types of pain that arise indirectly in the course of neurological disorders. Thus, based on a more liberal definition with a lack of gold standard, the prevalence of neuropathic pain continues increase, in some reports as high as 75% of the patients with chronic widespread musculoskeletal pain  and 37% of the patients with chronic low back pain without radiculopathy .
Thus, multiple diagnostic tests, without a gold standard and with a lack of demonstrated accuracy, lead to increased estimations of prevalence that will lead to an explosion of expensive drug therapy, which may lead to increasing disabilities.
While we appreciate the manuscript by Cohen and Mao , which is comprehensive and detailed, we would like to express our concern in reference to neuropathic pain which essentially is based on a subjective diagnosis. This harkens back to the explosion of opioid use in 1990s because a small study by Portenoy and Foley  allegedly showed the benefits of opioids in chronic noncancer pain resulting the major disaster of the century with numerous fatalities . Thus, it is essential to exercise caution in the diagnosis, and consequently, the recommendations of multiple treatments.
 Cohen SP, Mao J. Neuropathic pain: Mechanisms and their clinical implications. BMJ 2014;348:f7656.
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Competing interests: Dr. Falco is a consultant for St. Jude Medical Inc. and Joimax Inc.