The dermatoscope is to the skin as the otoscope is to the ear. Once you have examined the ear with an otoscope, it is hard to imagine examining the ear without one. The same is true for the dermatoscope and the skin. The dermatoscope allows you to see into the skin and make diagnoses with greater accuracy and confidence. The dermatoscope was originally used and studied to better diagnose skin cancers, but its use has been expanded into all aspects of dermatology including the diagnosis of scabies, alopecia, nail disorders, and inflammatory skin diseases.
The scope is called either the dermatoscope or dermoscope. The process of using the dermatoscope is interchangeably called dermoscopy or dermatoscopy.
Dermoscopy is a technique that allows clinicians to evaluate subsurface structures within the skin with an instrument called a dermatoscope (Figure 111-1). Most of the light shining onto the skin is scattered at the air-skin interface, resulting in back-scattered light (glare). The dermatoscope is a handheld device consisting of a 10× magnification lens and a transilluminating polarized or non-polarized light source designed to diminish surface glare to see into the deeper layers of the skin.
Various dermatoscopes. (Reproduced with permission from Richard P. Usatine, MD.)
NON-POLARIZED DERMOSCOPY (NPD)
Non-polarized dermatoscopes (NPDs) eliminate the air-skin interface with the glass faceplate of the dermatoscope and immersion fluid. The following liquids work well: ultrasound gel, mineral oil, and alcohol. Because of the lack of air bubbles and the clarity of the image, 70% alcohol is the preferred immersion liquid. For certain locations such as the nail, ultrasound gel is preferred, as it will not flow off the nail plate surface.1 NPDs primarily allow for the observation of structures located between the stratum corneum and superficial papillary dermis, with the superficial structures being more conspicuous (Figure 111-2).
Non-polarized dermoscopy. Light is transmitted via the dermatoscope—light source (blue, black, and red arrows). The red arrow represents the superficial penetrating light, the main source of contrast using non-polarized dermoscopy, which undergoes minimal scattering events. The black arrow represents the deep penetrating light, contributing a small fraction of the back-reflected light due to multiple scattering events. The blue arrow represents the surface glare, eliminated by the use of the immersion fluid.
POLARIZED DERMOSCOPY (PD)
Polarized dermatoscopes (PDs) are similar to NPDs with the main difference between the two being that PD uses two polarized filters to achieve cross-polarization, which eliminates the glare off the skin.2 One advantage of PDs is that they do not require direct contact with ...