Transfollicular delivery of gold microparticles in healthy skin and acne vulgaris, assessed by in vivo reflectance confocal microscopy and optical coherence tomography

Introduction Topical application of gold microparticles (GMPs) for selective photothermolysis is a recently FDA‐cleared therapy for acne vulgaris. Current evidence indicates the potential of optical imaging to non‐invasively visualize GMPs and describe photothermal tissue effects. Objectives To qualitatively and quantitatively describe GMP delivery in vivo and visualize laser‐mediated thermal effects of GMPs in facial skin of acne patients and healthy participants, using reflectance confocal microscopy (RCM) and optical coherence tomography (OCT). Methods Patients with facial acne (n = 14), and healthy participants (n = 7) were included. RCM and OCT images were acquired at baseline, after GMP application, and after diode laser exposure. All images were evaluated qualitatively and quantitatively with regards to GMP delivery in skin layers and morphological thermal effects. Lastly, skin biopsies were obtained to compare RCM and OCT findings to histology. Results GMPs were delivered equally in healthy participants and acne patients, and in lesional and non‐lesional acne skin. In RCM images, GMPs appeared as hyperreflective aggregates inside hair follicles and eccrine ducts, corresponding to natural skin openings (NSOs). The fraction of NSOs with hyperreflective content increased significantly after GMP application compared to baseline (50–75% increase, P = 8.88 × 10−16). Similarly, in OCT images, GMPs appeared as hyperreflective columns inside hair follicles and were not detected in surrounding skin. GMPs reached a maximum depth of 920 μm (median 300 μm). After laser exposure, RCM and histology revealed selective perifollicular tissue changes around NSOs. Conclusion Optical imaging visualizes GMP delivery and thermal tissue response following laser exposure and enables bedside monitoring of transfollicular microparticle delivery. Lasers Surg. Med. 51:430–438, 2019. © 2019 Wiley Periodicals, Inc.