Analysis of sweating by optical coherence tomography in patients with palmoplantar hyperhidrosis

Optical coherence tomography (OCT) is a high-resolution tomographic imaging technique that uses optical interference. OCT has enabled the non-invasive three-dimensional analysis of individual acrosyringia in the stratum corneum in human skin. However, no report on the measurement of sweating by OCT using clinical data from humans has been published to date. Twenty patients with hyperhidrosis and twenty healthy subjects were included in this study. Imaging of acrosyringia in the stratum corneum using OCT and measurement of the sweat rate using the ventilated capsule method were performed simultaneously. The hand grip exercise of the right hand was used as a load to induce sweating, and the left fingertip was measured before and after the exercise load. Five acrosyringia were extracted from each OCT image, and their volumes were calculated. The mean volume of each acrosyringium was divided by the thickness of the stratum corneum to calculate the mean cross-sectional area of the acrosyringium. Furthermore, the number of sweat droplets on the skin surface was measured. The mean cross-sectional area of acrosyringia after the load increased both in patients with hyperhidrosis and in healthy subjects (P < 0.001). The mean cross-sectional area of acrosyringia of patients with hyperhidrosis was larger than that of healthy subjects (P < 0.001). The mean cross-sectional area of acrosyringia and the sweat rate showed a positive correlation before and after the load (r = 0.88 to 0.91). The number of droplets also increased after the load (P < 0.001), and the number of droplets in patients with hyperhidrosis was higher than in healthy subjects (P < 0.001). Our study has shown that acrosyringia in the stratum corneum increase in proportion to the sweat rate. OCT is a rigorous and valuable method that can measure and quantify sweating in the body without being an invasive procedure.