The effects of menthol on cold allodynia and wind-up-like pain in upper limb amputees with different levels of phantom limb pain.

The mechanisms underlying phantom limb pain are not fully known, but hypersensitivity appears to be a central element. Menthol has previously been suggested as a model for hypersensitivity, but it has not yet been investigated if different levels of neuropathic pain may influence the effects of menthol or if topical application of menthol may act as a model for hypersensitivity in patients with phantom limb pain. In the present study, menthol (l-menthol 40%) was applied to the affected and non-affected sides in 24 upper-limb amputees with different levels of phantom limb pain to test if menthol could induce cold allodynia and exacerbate wind-up-like pain. The average level of phantom limb pain was significantly related to cold allodynia (P=0.044). Prior to application of menthol, the level of phantom limb pain was significantly related to the level of wind-up-like pain following both brush (P=0.040) and pinprick (P=0.033) stimulation. After application of menthol, the level of phantom limb pain was only related to wind-up-like pain following brush (P=0.011) but not pinprick stimulation (P=0.233). This study indicates that menthol does influence hypersensitivity in phantom limb pain patients, and it is the first study to show that menthol may exacerbate wind-up-like pain in this group of neuropathic pain patients. The findings suggest that menthol may act as a model for studying sensitization in phantom limb patients.