Principles and Technique of Dermoscopy and Videodermoscopy1
Dermoscope synonyms: Dermatoscope, skin surface microscope, epiluminescence microscope or episcope.
Introduction
A dermoscope is a noninvasive, diagnostic tool which magnifies subtle clinical surface features of skin lesions as well as unveils some subsurface skin structures not normally visible even with a magnifying lens. Some dermoscopic patterns are observed consistently with certain diseases and these then could be used for their diagnosis. Hence, this office procedure may sometimes obviate the need for a skin biopsy for diagnosis and for follow-up. The facility of storage of images and the results being immediately available are added advantages.1
In short, a dermoscope is functionally similar to a magnifying lens but with several add-on features of an inbuilt specialized illuminating system (visible light, polarized light, and ultraviolet sources), adjustable magnification, the ability to assess structures as deep as in the reticular dermis, and the ability to record digital images for future analysis and comparison.
Principles of Dermoscopy
The basic principle of dermoscopy is illumination (and transillumination) of a lesion with different light sources and studying it with a high magnification lens that may or may not be connected to a camera and computer.2 Any light ray incident on skin undergoes varying proportions of reflection, refraction, diffraction, and absorption dependent to physical properties of the skin (Fig. 1.1). Most of the light incident on dry, scaly skin is reflected, but smooth, oily skin allows most of the light to pass through it, reaching the deeper dermis improving visibility of subsurface features.
Fig. 1.1: Principle of a contact dermoscope (Reproduced with permission of Dr DM Thappa, Chief Editor, IJDVL from reference no. 1)
3Linkage fluids like oils applied over the lesions to be studied improve the translucency of the skin, although many modern day videodermoscopes do not require use of linkage fluids (Fig. 1.2). Various linkage fluids used are oils (immersion oil, olive oil, and mineral oil), water, an antiseptic solution, glycerin, and gels. A practical problem with use of oils as linkage medium is that, unless applied abundantly, they cause a lot of bubbles that may make the lesion difficult to visualize or photograph. Moreover, immersion oil is not used because it contains chlorinated paraffin and dibutyl phthalate, which have teratogenic, fetotoxic, and carcinogenic effects.3
4Water causes fewer bubbles but evaporates quickly and hence is less preferred than oils. Besides, their refractive index is not as close to that of the skin; hence, subsurface features may not be well seen. An evidence-based study by Gewirtzman AJ et al4 showed that a 70% alcoholic solution gives best results in terms of image clarity, eliminating air bubbles, and better patient tolerability, as it has less strong odor. We use commercially available antiseptic solutions containing 70% alcohol. These solutions are better tolerated by patients, as they also have an additional emollient and moisturizing effect. Their use also potentially decreases the rate of transmission of infections,5 as we deal with inflammatory dermatoses, which are likely to be excoriated and secondarily colonized with microorganisms. One can also use liquid paraffin, which is inexpensive, safe, and easily available, with good results. Air bubbles are more likely to form with paraffin oil.
Glass has a refractive index (1.52) similar to that of skin (1.55) and hence when placed over linkage fluids coated skin (as in contact plates), further enhances transillumination of the lesion. Gels (ultrasound gel) are useful, while doing dermoscopy of solid curved areas, particularly the area surrounding the nail plate.6 By using gels, the entire curved area of the nail can be viewed as the viscous gel fills up and remains in the space between the surface to be viewed and the contact plate unlike liquids which would escape out. Another indication of using gels as linkage fluid is while doing dermoscopy around the eye region, because unlike liquids, gel would not flow into the eyes.7
5Videodermoscopes with powerful light sources do not usually use linkage fluid thereby simplifying the procedure of dermoscopy further. This also allows them to show the surface features of the skin on “as is” basis that is needed to assess dryness or oiliness of the skin.
Parts of a Dermoscope
The essential components of a dermoscope are:
- Achromatic lens: Most basic instruments provide 10X magnification, but higher magnifications like 20X give better results and higher magnification or up to 1000X can be achieved with special lenses or with CCD cameras used in modern day videodermoscopes.
- Inbuilt illuminating system: Halogen lamps, which are oriented at an angle of 20°, placed within the handheld piece were the order of the day till recently. However, the color contrast of lesions gets altered by the yellow light of halogen lamps. Light emitting diodes (LED) are now standard sources that provide high intensity white light and consume 70% less power than halogen lamps. Illumination can be altered by turning off a set of LEDs. They are also designed to emit lights of different colors for better visualization of the skin as penetration of the skin by light is proportional to the wavelength of light.Use of polarized light sources has added a new dimension to videodermoscopy by allowing them to display subsurface features of skin lesions without the use of contact plates and linkage fluids. Further addition of ultraviolet light source 6allows fluorescence to be studied on a microscopic basis and its applications need more exploration.
- Power supply: Handheld instruments are usually powered by batteries and may have rechargeable handles (Delta 20™).
- Display or viewing system: While handheld dermoscopes have a simple viewing see-through viewing window, the videodermoscopes have the ability to connect to a computer or another display device or have their own display screen.
- Inbuilt photography systems: These have become an essential component of a dermoscope (not available as standard feature with handheld dermoscopes) because of the obvious need to record and store the images. The camera may be either an attachable conventional or digital camera or an inbuilt video camera, and supporting software, for the capture, storage, retrieval and even interpretation of images.
Technique
Dermoscopy can be done by either the non-contact or the contact technique. In the contact technique, the glass plate of the instrument comes in contact with the surface of the linkage fluid applied lesion (Figs 1.1 and 1.3). In contrast, in the non-contact technique, no linkage fluid is needed speeding up the procedure further. In the non-contact technique of videodermoscope, separate LEDs emit white light and polarized light and the image is captured by a CCD camera (Figs 1.2 and 1.4). While the non-contact technique ensures that there are no nosocomial infections,5 the ability to capture and store digital images on a computer truly puts a videodermoscope ahead of a contact dermoscope.7
Contact plates are made of multi-coated silicone glass and are of different types. Graduated plates have inscribed scales for measuring the lesion, while nongraduated plates lack a scale. Small plates have a small contact area to facilitate use in difficult to access regions like the web spaces, flexures and for nail fold capillaroscopy. Contact plates can be sterilized by using 2% glutaraldehyde, methylated spirit, boiling, or autoclaving.
Conclusion
Dermoscopes are not commonly used in developing countries, because they are relatively expensive and are not readily available.8
Their major use in the developed world is in the study of melanocytic nevi and melanoma in white skinned individuals. Their potential for study of inflammatory and pigmentary dermatoses is waiting to be tapped. 9
References
- Nischal KC, Khopkar U. Dermoscope. Indian J Dermatol Venereol Leprol 2005;71:300–3.
- William Stolz, Peter Bilek, Michael Landchaer, Amandcogneta. Basis of dermatoscopy and skin-surface microscopy. William Stolz, Peter Bilek, Michael Landchaer, Amandcogneta. Color atlas of dermatoscopy. 1st ed. Germany: Blackwell Publications; 1994. p.7-10.
- Binder M, Kittler H, Pehamberger H, Wolff K. Possible hazard to patients from immersion oil used for epiluminescence microscopy. J Am Acad Dermatol 1999;40:499.
- Gewirtzman AJ, Saurat JH, Braun RP. An evaluation of dermoscopy fluids and application techniques. Br J Dermatol 2003;149:59–63.
- Stauffer F, Kittler H, Forstinger C, Binder M. The dermatoscope: a potential source of nosocomial infection? Melanoma Res 2001;11:181.
- Ronger S, Touzet S, Ligeron C, et al. Dermoscopic examination of nail pigmentation. Arch Dermatol 2002;138:1327–37.
- Melski JW. Water-soluble gels in epiluminescence microscopy. J Am Acad Dermatol 1993;29:129–30.