Unmasked Neuropathic Pain After Neurectomy: A Case Series and Review of the Literature.

Localization of neuropathic pain to a specific peripheral nerve origin relies on patient history, physical examination, and nerve blocks. Neurectomy of the involved nerve(s) can successfully alleviate patients' pain. However, a subset of patients postoperatively describe persistent pain, but say that the pain "moved" to a new location (eg, from the dorsum of the foot to the lateral foot). This may be viewed as a treatment failure by the patient and surgeon alike. Further investigation, however, may localize the new pain to an additional, separate peripheral nerve injury, which was previously unrecognized by both parties. The mechanism involved is that of pain masking and unmasking. Successful treatment of the more prominent pain stimulus allows for recognition of a second, less-offending peripheral nerve injury. As the field of surgical treatment of chronic peripheral neuropathic pain advances, it is important to identify and define specific nuances of diagnosis and treatment via neurectomy. The term "diffuse noxious inhibitory control," used to describe the pain-inhibits-pain pathway, may help explain the phenomenon of masking, whereby one pain generator is more prominent and shields another site from recognition and subsequent diagnosis. In this context, unmasked pain should be considered as a potential source of surgical treatment failure. We present a series of patients who, following improvement in the initial location of their pain, reported pain in a distinctly new peripheral nerve distribution, leading to reoperation.