Using Mechanical Pain Sensitivity to Target Responders to Capsaicin 8% Patch Treatment
PALM SPRINGS, CA — Capsaicin 8% patch is a novel therapy for the treatment of peripheral neuropathic pain. Researchers at the 2012 American Academy of Pain Medicine Annual Meeting reported on using mechanical pain sensitivity (MPS) to identify patients who are more likely to respond to capsaicin patch treatment in order to improve treatment targeting.
Burkhard Gustorff, MD, of the Department of Anaesthesia, Intensive Care and Pain Medicine, Wilhelminenspital der Stadt Wien, Vienna, Austria, and colleagues assessed the efficacy of capsaicin 8% patch in 31 hospital outpatients over a 12-month period starting in April 2010. MPS was determined at baseline by estimating the stimulus response function (SRF) to fixed stimulus intensities (8 to 512mN) using a punctate probe. Somatosensory perception of both treated and contralateral untreated areas was tested with quantitative sensory testing (QST) prior to treatment, after 24 hours, 1 week, 1 month, and 3 months. Patients were considered responders if they experienced a ≥30% reduction at one month in numerical pain rating scale (NPRS) average pain from baseline.
Fifteen patients completed all observations, and eight responded to treatment (53%). At baseline, responders exhibited increased MPS over non-responders as characterized by SRF with higher intercept (+16.521 vs. +1.4849) and shallow slope (0.0498 vs. 0.1122). At one month, responders showed normalization of nociceptive function (reduced intercept, +6.2159; increased slope, 0.0848; P=0.055).
In this patient population, responders to capsaicin 8% patch treatment were characterized by baseline hyperalgesia to weak pinprick stimuli which resolved after treatment. Dr. Gustorff suggested that MPS testing could identify patients more likely to respond to capsaicin patch treatment.