Imaging modalities in trichology: Ultrasound, reflectance confocal microscopy, and optical coherence tomography

Although invasive techniques such as scalp biopsies and non-invasive techniques such as trichoscopy are commonly used for the diagnosis and management of alopecia, the latter does not always provide enough information on the state of the disease. Currently, we have new non-invasive diagnostic methods to complement the clinical and trichoscopic findings of patients with alopecia; these are high-frequency ultrasound (HFU), ultra-high-frequency ultrasound (UHFU), reflectance confocal microscopy (RCM) and optical coherence tomography (OCT), which are capable of identifying structures under the surface of the scalp, while maintaining the ability to monitor hair shafts. This review describes the main features reported with each technique for the different types of alopecia -scarring and non-scarring- with the aim of identifying those parameters that may contribute to clarifying new pathophysiological findings, while adding information to the trichoscopic examination and improving diagnostic processes and monitoring.