Non-invasive real time imaging of mite skin infestation with line field confocal optical coherence tomography

Introduction Mites affecting humans remain a widespread health issue. Among others, dermatologists need to deal with biting mites vectoring scrub thypus, house dust mites causing type I sensitisation, Sarcoptes scabiei as a vector of scabies and Demodex folliculorum associated to rosacea and Demodex folliculitis. Diagnosis is based on clinical features, skin scraping cannot always be performed. Scabies is a contagious, globally wide spread human skin infection. Caused by the scabies agent ectoparasite Sarcoptes scabiei var. hominis, its frequently occurring outbursts in communities lead to a significant health as well as economic burden. The process of diagnosing scabies is based on characteristic clinical features like a progressive rash or inflammatory excoriated papules. Moreover, the use of dermoscopy allows to visualize typical dermoscopic signs of a scabies infestation, for instance the so-called “delta”, “kite” or “triangle”, representing the anterior body of an adult female mite at the end of a burrow. Identifying mites, eggs or faecal pellets through skin scraping, with the help of a high magnification device or dermoscopy are already established criteria to diagnose scabies. Furthermore reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) have already been used to non-invasively detect scabies infestations. In addition to that, the new diagnostic imaging device Line-field confocal coherence tomography (LC-OCT) is not only able to provide a painless, real-time bedside visualisation of scabies mites inside human skin but also allows their therapeutic monitoring. Material and Methods Based on a two-beam interference microscope with line illumination and line detection scans with a cellular resolution (1.1 μm x 1.3 μm) can be provided. The device has three different imaging modalities: en-face, en-coupe and 3D. Results By using the en-coupe mode and 3D reconstruction, the exact location of the mite inside the epidermis and the Stratum corneum can be discovered. S. scabiei appear as an ovoid structure with a thin, corrugated exoskeleton and triangular spicules. Additionally, the detection of skybala and eggs as roundish, mainly hyperreflective structures, is possible. Demodex mites are visible inside the hair follicles, in vertical mode as elongated hyperrefrective structures, while in en-face mode as solitary or more frequently multiple, roundish, hyperreflective structures. Discussion Non-invasive in-vivo examination of mites is able to provide a fast, painless diagnosis at bedside. An advantage of LC-OCT in comparison to conventional OCT is a higher, almost cellular resolution. Although its resolution is still lower than in RCM scans, the opportunity to combine the en-face mode with the en-coupe mode and the 3D imaging modality allows a high resolution and penetration depth. Besides detecting burrows, eggs and skybala, LC-OCT allows exact special correlations and measurement of structures. As a result immediate diagnosing of scabies and Demodex infestation and non-invasive therapeutic monitoring is possible. Therefore we see a high potential in the use of LC-OCT in the daily dermatologic practice in the future, with its diagnostic value not only limited to skin cancer diagnostics but also to be used in skin infestations.