Capsaicin is the pungent ingredient of chili peppers and is approved as a topical treatment of
neuropathic pain. The
analgesia lasts for several months after a single treatment.
Capsaicin selectively activates TRPV1, a Ca2+-permeable cationic
ion channel that is enriched in the terminals of certain nociceptors. Activation is followed by a prolonged decreased response to noxious stimuli. Interest also exists in the use of
injectable capsaicin as a treatment for focal
pain conditions, such as
arthritis and other musculoskeletal conditions. Recently injection of
capsaicin showed therapeutic efficacy in patients with
Morton's neuroma, a painful foot condition associated with compression of one of the digital nerves. The relief of
pain was associated with no change in tactile sensibility. Though injection evokes short term
pain, the brief systemic exposure and potential to establish long term
analgesia without other sensory changes creates an attractive clinical profile. Short-term and long-term effects arise from both functional and structural changes in nociceptive terminals. In this review, we discuss how local administration of
capsaicin may induce ablation of nociceptive terminals and the clinical implications.