AUSTIN, TX—A 50-year-old male who presented with a 3–4 year history of burning pain to the plantar and dorsal aspects of his feet and big toes was successfully treated with an 8% capsaicin patch (Quetenza), according to a case report presented during the American Pain Society 30th Annual Scientific Meeting.
Ryan Michaud, MD, of the University of Utah, Salt Lake City, and colleagues noted that previously, the patient had negative workups for diabetes, HIV sensory neuropathy, and ischemic neuropathy. His history revealed no significant nutritional abnormalities, or chemical, toxic, or chemotherapeutic agent exposure. The investigators believed his neuropathy was secondary to an initial frostbite injury.
The patient experienced minimal pain relief when taking pregabalin 50mg in the morning and 125mg in the evening with one to two tablets of hydrocodone/APAP 7.5/500mg every day as needed. Previous trial treatments, comprised of tricyclic antidepressants, gabapentin, Lidoderm patches, and other opioid medications, were intolerable due to adverse effects. Subsequent treatment with pregabalin resulted in minimal help as investigators were unable to escalate his dose secondary to increased somnolence. When treated with capsaicin 8% topical patch, he reported a >50% reduction in pain at a one month clinic visit follow up.
Topical capsaicin acts as an agonist of the transient receptor potential vanilloid 1 (TRPV1) receptor. This receptor is initially activated by capsaicin through depolarization of nociceptive sensory nerve endings, which generates electrical excitation and initiates signal transmission to the spinal cord, the investigators reported.
One theory of the analgesic effect of capsaicin is continued capsaicin exposure at the TRPV1 receptor can lead to “defunctionalization” or impairment of nociceptor function. Another theory is that an impairment of retrograde transport of neuropeptides like nerve growth factor may play a role in attenuating sensory neuronal hyperexcitability and temporarily depleting nociceptor nerve endings in the epidermis.
The investigators found that epidermal nerve fibers (ENF) density were reduced an average of 80% from a single application of capsaicin 8% transdermal patch for one hour on the bilateral thigh of healthy adults, leading to the possible conclusion that neurodegeneration may also account for this patient’s pain relief.