|SYMPOSIUM: BASICS OF DERMOSCOPY AND DERMOSCOPIC PATTERNS
|Year : 2020 | Volume
| Issue : 2 | Page : 69-73
Basic science of dermoscopy
Balachandra S Ankad, SV Smitha, Varsha R Koti
Department of Dermatology, S. Nijalingappa Medical College, Bagalkot, Karnataka, India
|Date of Submission||21-Apr-2020|
|Date of Decision||14-Jun-2020|
|Date of Acceptance||26-Jun-2020|
|Date of Web Publication||18-Aug-2020|
Balachandra S Ankad
Department of Dermatology, S. Nijalingappa Medical College, Navanagar, Bagalkot - 587 102, Karnataka
Source of Support: None, Conflict of Interest: None
Introduction: Dermoscopy is a non-invasive tool which demonstrates characteristic patterns in many dermatoses. To understand dermoscopy, basic elements, vascular structures and pigment netwrok should be dealt with. One needs to understand the concept of basic physics of dermoscopy and cross polarization. Non-polarized and polarized lights show particular patterns in prominence. Hence both are complementary to each other. It is recommended to use both lights in clinical practice. Essentially, dermoscopic features should be analyzed and interpreted in terms of pattern of dermoscopic changes, predominant color and any specific clues present in the lesion. This is basic approach to a given lesion to arrive at accurate diagnosis dermoscopically. Aim: To understand the basic principles of dermoscopy and the types of dermoscopy. Summary: Dermoscopy is a rapid method that involves the use of a hand-held device with a built-in illumination and magnification systems. It is an in-vivo technique to observe the surface and subsurface structures in the skin layers. In the past, it was employed exclusively to diagnose and rule out melanoma in a given pigmented lesion. Its confirmed utility in inflammatory and infective dermatoses has enhanced its popularity as dermatologist's stethoscope.
Keywords: Contact dermoscopy and non-contact dermoscopy, cross polarization, dermoscopy, principle
|How to cite this article:|
Ankad BS, Smitha S V, Koti VR. Basic science of dermoscopy. Clin Dermatol Rev 2020;4:69-73
| Introduction|| |
Dermoscopy is a rapid method that involves the use of a handheld device with a built-in illumination and magnification system. It is anin vivo technique to observe the surface and subsurface structures in the skin layers. In the past, it was employed exclusively to diagnose and rule out melanoma in a given pigmented lesion. It has extended its applications to the diagnosis of inflammatory, infective, and granulomatous disease as well. Basically, the very intension of dermoscopic visualization of skin lesion is to observe the structures in the different layers of the skin.
| Tool|| |
Instruments are of two types: (i) handheld dermoscope (very small, handy, portable like an ophthalmoscope) and (ii) videodermoscope, comes with USB port that it should be attached to a computer system to visualize the dermoscopic patterns. Handheld dermoscopes are easy to handle and can be carried to many places for the examination of a skin lesion, whereas videodermoscopes have to be attached to computer system. Tool is called as dermoscope and the method is named as dermoscopy.
| Synonyms|| |
- Epiluminescence microscopy
- Skin surface microscopy
- Trichoscopy (dermoscopy of hair)
- Onychoscopy (dermoscopy of nails)
- Inflammoscopy (dermoscopy of inflammatory conditions)
- Mucoscopy (dermoscopy of mucosal surface)
- Entemodermatoscopy (dermoscopy of infestations).
| Dermoscope|| |
The parts of dermoscope include lighting or illumination system, magnification, and power supply. Lighting system consists of light-emitting diode lamps and they are mainly used in many handheld dermoscopes. Earlier devices employed halogen lamps. The magnification is provided by the achromatic lenses which are present in the faceplate of the dermoscope. Rechargeable lithium batteries produce power supply in handheld dermoscopes, whereas electric power supply is utilized in videodermoscopes [Figure 1]a.
|Figure 1: (a) Handheld dermoscope with power button (black arrow), polarized and non-polarized knob (yellow arrow), brightness enhancing knob (red arrow), and faceplate of dermoscope (blue arrow). Inset: Illumination system with the circular arrangement of light-emitting diode lamps. (b) Dermoscope is attached to a smartphone by a universal adaptor for quick attach and detach. (c) Clinical image of a hyperpigmented plaque suggestive of hypertrophic lichen planus. (d) Schematic diagram depicting the physics of cross polarization. Source and detector polarizers are placed perpendicularly. Detector polarizer allows nonpolarized absorbed light from the skin surface that has lost its phase or polarization(green arrow) whereas it blocks the reflected polarized light that has retained its phase or polarization (yellow arrow). (e) Dermoscopy of Figure 1c (hypertrophic lichen planus) in nonpolarized mode shows comedone-like opening (red arrows), white scales (blue arrows), and bluish-gray background (yellow arrows). Note the prominence of surface scales and comedo-like openings and ill-visualization of blue color as it is deep in the dermis. (f) Dermoscopy of Figure 1c (hypertrophic lichen planus) in noncontact polarized mode shows better visibility of bluish-white background (yellow arrows), brown pigment globules (green arrows), and white shiny streaks (black arrows). Appreciate the less prominence of comedone-like opening (red arrows) and lesser scales in this image. (g) Dermoscopy of Figure 1c (hypertrophic lichen planus) in contact polarized mode using ultrasound gel as interface medium shows clearer and enhanced visibility of brown pigmented areas (green arrows), white shiny streaks (black arrows) and bluish-gray background (yellow arrows). Comedo-like openings are appearing as brown globules (red arrows) and scales are not visible. (h) Demonstration of the faceplate of dermoscope being 'suspended' in the space of viscous ultrasound gel (black arrow) and by taking support from little finger (red arrow) to avoid pressure effect on the lesion|
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Most of the handheld dermoscopes are attached to smartphone to capture the images [Figure 1]b, whereas videodermoscopes allow the simultaneous visualization of dermoscopic patterns on a computer screen and there is a facility to save the images. Magnification is up to ×14 in the conventional handheld dermoscopes. Videodermoscopes provide even higher magnification up to ×160 to ×220 as well.
| Principle|| |
The basic question is why human eyes are unable to see the structures that are below the skin surface layer. The answer is that the refractive indices of stratum corneum (1.55) and air (1.0) are different. This produces reflection of light that is incident on the skin surface and results in the invisibility of structures to the human eyes. To avoid reflection of light and enhancing the penetration of light, a fluid interface dermoscope and the skin surface is used. Fluid must have refractive index closer to that of the stratum corneum.,, This is achieved using interface medium or by employing noncontact polarized light. Both make better visualization of skin structures.
| Technique of Dermoscopy|| |
Polarized and nonpolarized dermoscopy are two different techniques of dermoscopy that enable physicians to visualize the different structures present in the skin layers to assist in the detailed analysis of dermoscopic patterns. When natural light is incident on the skin surface, light undergoes refraction, diffraction, maximum of it undergoing reflection, and minimal amount of it absorbed by the object. Hence, our eyes cannot visualize the deeper structures in a given skin lesion. For example, a lesion of hypertrophic lichen planus appears as well defined bluish plaque without much detail [Figure 1]c. To visualize deeper structures, this “specular reflectance” has to be minimized. This is achieved either using a glass plate of optimal refractive index and interface medium in between or using a technique called “polarized dermoscopy.”
In polarized dermoscopy, two special filters will be held orthogonally at 90°. The light passing through the first filter (source polarizer) maintains its phase or polarization. When it is incident on stratum corneum, most of it is reflected back from the stratum corneum and is blocked by the second filter (detector polarizer) because it is in phase or polarization. The polarized light which is absorbed and scattered by deeper structures skin will lose its polarization and easily passes through the second filter to enter the light detector, thereby allowing the visualization of deeper structures of the skin up to 100 microns depth. This technique which allows the light which has lost its polarization to pass through the second filter with additional blocking of the reflected light which maintains its polarization is known as “cross-polarization” [Figure 1]d.,
Nonpolarized dermoscopy requires contact with skin surface and the interface medium. Nonpolarized dermoscopy is used for better visualization of superficial structures such as comedones, milia-like cysts, crypts, fissures, and scales [Figure 1]e. Polarized dermoscopy is more conspicuous in viewing deeper structures such as pigment network and vessels [Figure 1]f. Hence, both the modes are complementary to each other for the better visual perspective of the lesions.
Commonly used interface fluids include 70% ethanol, 90% isopropanol, ultrasound gel liquid paraffin, and water. Most preferred medium is ultrasound gel because of it viscosity, semitransparent, and inert nature. And also, it is used exclusively for nail examination (convex surface) and for the lesions near the eyes (does not trickle down).
| Concept of Contact Polarized Dermoscopy|| |
As mentioned above, nonpolarized dermoscopy requires both surface contact and interface medium, whereas polarized dermoscopy is performed without contacting skin surface. Recently, many leading dermoscopists around the world are using contact version-polarized dermoscopy. That means touching the surface with lights in polarized mode. This is for better illumination, visualization, and resolution of structures [Figure 1]g. The main drawbacks of this technique are the compression of blood vessels and cross infection. To overcome former limitation, we would suggest that faceplate of the dermoscope should be 'suspended' in the space of viscous ultrasound gel by holding the scope and by keeping the little finger by the side of lesion for the support of to avoid/keep exert minimum pressure [Figure 1]h. To solve the latter shortcoming, disposable contact caps, food wraps adhesive tapes, and glass slides are used between the faceplate and skin lesions. Thus, it is advisable to perform nonpolarized, noncontact-polarized, and contact-polarized dermoscopy of a given lesion to make sure that minor details are not missed.
| The Language of Dermoscopy|| |
To acquire complete knowledge and to adopt mastery in the field of medicine, knowing the basic aspects of the field is essential. A postgraduate student of dermatology learns primary and secondary lesions as soon as the student enters the course of dermatology. In a similar way, to learn dermoscopy, understanding the basic elements and vascular structures in dermoscopy is of utmost importance.
Basic elements in dermoscopy include (i) lines which are solid objects with length exceedingly more than width [Figure 2]a, (ii) “globules” which are irregular solid objects with definite shape and size [Figure 2]b, (iii) “pseudopod” which is bulbous extension at margins of a line [Figure 2]c, (iv) “dots” which are tiny small solid objects not enough to be designated as globules [Figure 2]d, and (v) “circles” which are solid ring-like objects with equidistant margins from the center [Figure 2]e. In addition, 'structureless areas' are the areas large enough to form patterns, but without any discernible elements in them [Figure 2]f.
|Figure 2: (a) Dermoscopy image of neurofibroma depicting white and brown lines (black arrows). Inset: Schematic diagram. (b): Dermoscopy image of melanocytic nevus showing clods (red arrows). Inset: Schematic diagram. (c) Dermoscopy image of Spitz nevus revealing pseudopods (yellow arrows). Inset: Schematic diagram. (d) Dermoscopy image of lichen planus pigmentosus depicting dots (black arrows). Inset: Schematic diagram. (e) Dermoscopy image of annular lichen planus showing circles (red arrows). Inset: Schematic diagram. (f) Dermoscopy image idiopathic guttate hypomelanosis revealing structureless area (red arrow). Inset: Schematic diagram|
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Vascular structures in dermoscopy are described in the literature that consist of (i) dotted vessels – red dots with diameter of 0.01–0.02 mm and represent tips of the vertically aligned vessels [Figure 3]a, (ii) linear vessels – red lines that may be regular or irregular or helical in shape [Figure 3]b, (iii) slightly curved short linear (comma-like) vessels [Figure 3]c, (iv) linear branching (arborizing) vessels – large vessels with big stems that arborize into smaller, thinner branches in nonhomogenous fashion like tree branches [Figure 3]d, (v) linear vessels with loops (hairpin vessels) – long thin vessels that are looped at one end [Figure 3]e, and (vi) short linear twisted (glomerular vessels) – short and thin vessels that are interpenetrating vessels as balls of wool which resembles renal glomeruli.
|Figure 3: (a) Dermoscopy image of psoriasis depicting red dotted vessels (blue arrows). Inset: Schematic diagram. (b) Dermoscopy image of granuloma demonstrating linear vessels (black arrows). Inset: Schematic diagram. (c) Dermoscopy image of prurigo nodularis depicting comma-like vessels (yellow arrows). Inset: Schematic diagram. (d) Dermoscopy image of basal cell carcinoma showing arborizing vessels (black arrows). Inset: Schematic diagram. (e) Dermoscopy image of keratoacanthoma revealing hairpin vessels (green arrows). Inset: Schematic diagram|
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Pigment network is the basic pattern commonly observed in dermoscopy. Melanocytic lesions consist of pigment network which becomes distorted or atypical in melanoma. Pigment network is categorized into (i) typical, (ii) atypical, and (iii) pseudonetwork. A typical pigment network is characterized by uniform darker lines in width and color and hypopigmented holes [Figure 4]a. These holes and intersecting lines constitute grid-like reticular pattern. It is seen in most of the body parts. Atypical pigment network consists of irregularly meshed with lines varying in size, color, thickness, or distribution and is specifically observed in melanoma [Figure 4]b. Pseudonetwork is seen exclusively in face in which rete ridge pattern is flat and typical pigmentation is not seen. Instead, normal pigmented area is pierced by the openings (holes) of follicle and eccrine openings which appear as pigment network [Figure 4]c.,
|Figure 4: (a) Dermoscopic image of typical pigment network showing grid-like arrangement of darker pigmented lines with hypopigmented holes. This is termed as reticular pigment network. (b) Dermoscopy image of atypical pigment network in melanoma showing irregular pigmentation with irregular lines at the periphery (arrows). (c) Dermoscopy image of pseudonetwork in melasma showing normal hypopigmented area (red arrows) is pierced by holes of eccrine and follicular openings (yellow arrows). Appreciate the difference between this and reticular pigment network in Figure 4a|
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Hence, in the practice of dermoscopy, the first step is to analyze the pattern which implies arrangement of basic elements in a particular fashion. The second step is to observe for the color variegations to confirm the cause and location of color. The third step is to finding of a clue. Clues are not present in every lesion and if present, clues are specific to diagnosis. For example, nevus depigmentosus demonstrates white structureless areas with peripheral extensions on the background of faint uniform pigment network. Here, pattern is structureless area, color is white and peripheral extensions are the clues. It should be noted that dermoscopic pattern in a particular condition must be repetitive, recognizable, and must be observed by everybody. Importantly, dermoscopic features should correlate well with histopathological changes.
To conclude, dermoscopy has become a popular tool among the dermatologists around world and in India as well. The number of dermoscopists is ever increasing. No doubt, it assists in the accurate diagnosis in few dermatoses, and in some, it reduces the number of differentials of a lesion. Although it is not replacement for histopathology, it is definitely a promising adjunctive method for diagnosis in the clinical practice in terms of confirmation of a clinical diagnosis. It increases the compliance of patient's faith in the clinician as patient can see the virtual image of skin lesion. Hence, dermoscope is aptly called as dermatologist's stethoscope.
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