Photo Credit: RossHelen

The following is a summary of “Topical capsaicin modulates the two-point discrimination threshold—Modulation depends on stimulation modality and intensity,” published in the August 2024 issue of Pain by Frahm et al.

Spatial acuity, which influences pain sensitization and is the ability to narrow down the sensory output, is tested by a 2-point discrimination threshold (2PDT).

Researchers conducted a retrospective study to examine 2PDTs for mechanical and heat stimulation at various intensities modulated by topical capsaicin sensitization.

They divided 30 healthy individuals into capsaicin and placebo groups. The test was performed using mechanical and thermal (laser) stimulation, delivered at innocuous and noxious intensities, determined at baseline, and re-assessed for 48 hours. In the follow-up session, the individuals either had a capsaicin patch (8%) or a placebo patch 30 min before retesting the 2PDT.

The results showed  2PDT as highly dependent on stimulation modality and intensity. Innocuous mechanical stimuli (40.0 mm, 95% CI 38.1–41.9 mm were the lowest, and the highest 2PDT was for innocuous thermal stimuli (81.7 mm, 95% CI 73.9–89.5 mm). Topical capsaicin elevated the 2PDT. There was an increased intensity in stimuli following capsaicin, which was higher for noxious stimuli than for innocuous stimuli (ANOVA, P < 0.001).

They concluded that capsaicin showed increased pain sensitization in the 2PDT, and its testing using innocuous mechanical stimuli showed less variable results, indicating that 2PDT is suitable for detecting spatial acuity.

Source: onlinelibrary.wiley.com/doi/10.1002/ejp.4701