More than 50% of patients complain of hypersensitivity in the amputation stump, and chronic pain, in both the residual limb and the area referred to the body part removed. Rosario Privitera et al. conducted a functional MRI study to determine the efficacy of a single 60 minute application of capsaicin 8% patch in minimising chronic amputation stump and phantom limb pain, associated hypersensitivity with quantitative sensory testing, and changes in brain cortical maps using functional MRI (fMRI) scans.

The study enrolled 14 patients with single limb amputation with a pain intensity on the Numerical Pain Rating Scale ≥4/10 for a chronic stump or phantom limb pain. The study outcomes included assessment of pain, quantitative sensory testing, and fMRI (for the lip pursing task) at baseline and 4 weeks after application of capsaicin 8% patch to the amputation stump. The previous studies indicated a correlation between the shift into the hand representation area of the cerebral cortex with the lip pursing task and phantom limb pain, but in this study, fMRI clinical model for cortical plasticity was used.

The result showed that a mean reduction of −1.007, −1.414), and −2.029 was observed in spontaneous amputation stump pain, phantom limb pain, and evoked stump pain respectively. A marked decrease of −165 cm2, −80% (p=0.001) and −132 cm2, −72% (p=0.001) in the areas of brush allodynia and pinprick hypersensitivity in the amputation stump was also observed respectively. fMRI analysis contributed objective evidence of the restoration of the brain map, that is, reversal of the shift in the hand representation of the cerebral cortex with the lip pursing task (p<0.05).

At last, it was inferred that capsaicin 8% patch treatment might significantly reduce leads chronic pain mainly, in the area of stump hypersensitivity, enabling patients to wear prostheses, thus improving mobility and rehabilitation. Further, it was reported that phantom limb pain ("central" strain) and associated brain plasticity might be modulated by peripheral inputs, which can be ameliorated by the peripherally restricted effect of the capsaicin 8% patch.