1. 2022;25;E641-E647Capsaicin 8% for Peripheral Neuropathic Pain Treatment: A Retrospective Cohort Study
   Observational Study
   Joana Pinto, MD, Cristina Cardoso, APRN, Maria do Ceu Loureiro, MD, Alfredo Mendes de Castro, MD, Ines Ferreira Vieira, MD, and Jose Pedro Assuncao, MD.

BACKGROUND: Chronic neuropathic pain is a disabling condition that affects quality of life. Despite recommendations and guidelines, treatment remains suboptimal as it often does not result in significant symptom relief. Capsaicin 8% patch has been used for the treatment of several peripheral neuropathic pain etiologies with encouraging results.

OBJECTIVES: To assess the results of capsaicin 8% patch on neuropathic pain by evaluating pain intensity and the painful treatment area.

STUDY DESIGN: Observational retrospective cohort study.

SETTING: All patients submitted to capsaicin treatment at the Chronic Pain Unit of the Hospital Centre of Tondela Viseu, from 2011 through 2019.

METHODS: Records of capsaicin treatments were reviewed, and the data collected. The primary outcome was pain intensity and painful treatment area reduction between the first and last treatment. Also, the number of treatments performed, neuropathic pain duration, anatomic location, pain etiology, and concomitant oral pain medication at baseline and upon treatment conclusion was also listed.

RESULTS: Postsurgical neuropathic pain was the most common etiology (49%), followed by postherpetic (28%). The median (interquartile range [IQR]) baseline pain intensity assessed by the Numeric Rating Scale (NRS-11) was 6 (5-8) and the median (IQR) final NRS-11 was 3 (1-5), with a median (IQR) relative difference of -0.5 (-0.85-0.17) with statistically significant differences (P < 0.001) between baseline and last pain intensity, regarding all groups. Also, there was a reduction in the painful treatment area between baseline and the last evaluation, with a median (IQR) relative difference of -0.4 (-0.625-0.167).

LIMITATIONS: A relatively small sample and occasional different timing for pain intensity and pain treatment area assessment due to logistical difficulties.

CONCLUSIONS: Capsaicin 8% patch is a valuable option for the treatment of peripheral neuropathic pain, providing a significant reduction in pain intensity and painful area. It is well tolerated and has a high treatment compliance.

Ethics Committee Reference Number: 16/16//04/2021

KEY WORDS: Capsaicin, chronic pain, neuralgia, neuropathic pain, topical administration