The Mite-Gallery Unit: A New Concept for Describing Scabies through Entodermoscopy

Abstract

Scabies has always represented a diagnostic challenge for dermatologists, especially in subclinical cases or in atypical ones due to the coexistence of other diseases. Fortunately, dermatoscopy has enabled easier and faster in situ diagnosis. The aim of this study is to examine old and new dermatoscopic signs that Sarcoptes scabiei produces on the skin during its whole life cycle through entodermoscopy (dermatoscopy with an entomological focus) which, unlike traditional optical microscope examination, allows the local micro-environment to be preserved intact. Patients were enrolled during outbreaks of scabies from hospitals or nursing homes for the elderly in Bari (Italy). The study was performed applying both immersion and polarized dry dermatoscopy. The systematic use of dermatoscopy highlighted the morphological complexity of the Sarcoptes tunnel that had been described previously as a simple unitary structure. On the contrary, it is possible to distinguish three separate segments of the burrow that introduce a new anatomo-functional concept called the Mite-Gallery Unit (MGU). This approach, based on the mite life cycle and local skin turnover (the latter usually being ignored), allows the dermatologist to recognize not only Sarcoptes using the gallery, but also new descriptors including tunnels without Sarcoptes, those with acari alone, and those with associated signs of inflammation. The diagnosis of scabies using optical microscopy until recently has always involved demonstrating the mite and its products outside the human body (on a glass slide) without taking into account exactly what happens within the epidermis. Entodermoscopy is a term used to encapsulate both the presence of the parasite, the usual target of microscopy, and the changes produced in the superficial layers of the epidermis in situ. Thus, the scabies tunnel or burrow can be shown to be composed of three parts, the Head, Body, and Tail, in which different events affecting both mite and host develop. The Mite-Gallery Unit provides a new anatomical and functional explanation of scabies because it provides a more comprehensive in vivo and in situ dermatoscopic diagnosis. In this respect, dermatoscopy takes into account the behavior of the mite in addition to its interaction with its habitat, the human skin.

Keywords: Dry Dermatoscopy (d-DS); Enhanced Dermatoscopy (e-DS); Entodermoscopy (EDS); Mite-Gallery Unit (MGU); Wet Dermatoscopy (w-DS).

Figure 1

Objective examination of scabies in adults (L) and children (R).

Figure 2

The Mite-Gallery Unit (MGU) in non-polarized dry dermatoscopy (d-DS).

Figure 3

Dry dermatoscopy vs. wet dermatoscopy (w-DS) of the same Mite-Gallery Unit.

Figure 4

Content of the gallery. An MGU in enhanced wet dermatoscopy mode.

Figure 5

The Body of the mite. Enhanced wet dermatoscopy of an MGU in w-DS mode. In addition to refraction of its anterior part, Sarcoptes scabiei shows an opalescent body with several scattered dark dots (ladybird sign). These structures correspond to the “bristles” on the body that enable, amongst other things, the adherence of the mite within the tunnel.

Figure 6

Enhanced dermatoscopy of the MGU’s roof in non-polarized dry mode (d-DS). The body of the gallery is not completely intact due to numerous holes which give it a riddled aspect. From these openings the larvae of the Sarcoptes are believed to exit. On the right, one can see the reflective front part of the mite. At the bottom, dermatoscope LEDs are reflected on the serous exudate.

Figure 7

Moulting pocket in dry dermatoscopy with non-polarized (L) and polarized light (R). In this structure the complete Mite-Gallery Unit does not develop because the mite remains stationary until the moulting process is completed or mating happens. There is instead only a small whitish raised area (arrows, L-R), corresponding to the whole body of the Sarcoptes, behind which a real tunnel is not visible (R). Around the pocket, an area of erythema with blurred borders is easily recognizable.

Figure 8

Scabies pseudo-follicular exanthema observed in non-polarized dry dermatoscopy. Folliculitis-like lesions (L) are commonly considered to be a non-specific sign of scabies (L). In dermatoscopy, only a peri-ostial erythematous halo is appreciated with some pinpoint-like vessels inside it (R). There are no signs of a complete or atypical MGU.

Figure 9

Inflammatory response to an MGU observed under polarized light dry dermatoscopy of a hand lesion. Next to the mite (black arrows, L-R) the skin is normal, while in the central part of the gallery an erythematous halo (red arrow, L) is evident. Immediately behind the mite, inflammation can also occur in microvesicles trapped in the epidermis (red arrow, R). The tail of the gallery is characterized by keratin collarettes.

Figure 10

Nodular scabies observed in wet (L) and dry polarized light (R) dermatoscopy. A mite is easily recognizable in one of the axillary (insert) papules of a subject of African ethnicity (arrow, L). A buttock (insert) nodule present for a few weeks appears uninhabited instead (R).

Figure 11

Dry dermatoscopy with polarized light of an atypical MGU. Two mites (arrows) can be recognized behind which there is no tunnel but an erythematous area with polycyclic borders.

Figure 12

Dry dermatoscopy with non-polarized light of an atypical MGU. The refractive part of the mite (arrow) is evident, behind which there is an aggregate of scales rather than an ordinary gallery.

Figure 13

Evolution of an MGU towards a “ghost gallery” under polarized dry dermatoscopy. Three different examples. A mature MGU ends with a tail made up of keratinised collarettes that progressively move away from each other (black arrow, L). Sarcoptes is identifiable in the front part of the burrow (circle, L). When the mite is at the end of its life cycle or after therapy, the other parts of the tunnel undergo the normal processes of remodelling of the skin (C), forming the thin and polycyclic keratinic edges of a ghost gallery (C/R).