Dermoscopy

32 Dermoscopy



Dermoscopy allows the clinician to observe morphologic structures below the surface of the skin that are otherwise not visible to the naked eye. Many of the dermoscopically observed structures have direct histopathology correlates. In addition, the presence or absence of dermoscopic structures, their association with each other (i.e., certain structures are often seen together such as milia and comedo openings in a seborrheic keratosis), and their distribution within a lesion often lead to a specific diagnosis. Thus, it should come as no surprise that dermoscopy improves the clinician’s diagnostic accuracy. Dermoscopes are relatively inexpensive and easy to use and master. Start with this chapter and consider attending dermoscopy courses, visiting websites, and reading books on the subject once you have your dermatoscope and are ready to extend your learning.



Advantages of and Evidence for Dermoscopy


In two separate meta-analyses, dermoscopy had significantly higher discriminating power than clinical examination for experienced users.13 It is intuitively obvious that this improved diagnostic accuracy translates into improved patient management. For example, in one study, the malignant-to-benign ratio improved in dermoscopy users from 1 : 18 to 1 : 4.4


Primary care physicians (PCPs) who were given a 1-day training course in skin cancer detection and dermoscopic evaluation were able to improve their sensitivity for melanoma diagnosis. The study randomly assigned PCPs to the dermoscopy evaluation arm or the naked-eye (no dermoscopy) evaluation arm. The study showed that 23 malignant skin tumors were missed by PCPs performing naked-eye observation, whereas only 6 were missed by PCPs using dermoscopy (P = 0.002). The authors concluded that the use of dermoscopy improves the ability of PCPs to triage lesions suggestive of skin cancer without increasing the number of unnecessary expert consultations.5


Dermoscopy can help in the following ways:














Equipment


Dermoscopes illuminate the skin via the use of light emitting diode (LED) lights with or without the use of polarizing filters. Although most units are either nonpolarized (no polarizing filters in place) or polarized (polarized filters used), a few newer units, known as hybrids, allow the operator to toggle between polarized and nonpolarized light within the same unit. Nonpolarized dermoscopes (NPDs) are manufactured by Heine and Welch Allyn (Figure 32-1A). 3Gen manufactures NPDs, polarized dermoscopes (PDs), and hybrid dermoscopes (Figure 32-1B). A number of new dermoscopes attach to smart phones for easy dermoscopic photography.



Dermoscopic images seen with and without polarization can appear quite different, often providing complementary information. During naked-eye examinations of the skin, much of the light emitted toward the skin is reflected off of the stratum corneum due to the higher reflective index of the stratum corneum as compared to that of air. This precludes the observer from seeing structures below the stratum corneum. Nonpolarized dermoscopes require direct contact between the lesion and the glass plate of the dermoscope. In addition, the presence of a liquid interface (i.e., alcohol or oil) between the lesion and the glass plate is mandatory. The elimination of the air interface and the presence of the liquid reduces the amount of light reflected off the stratum corneum, thereby allowing the observer to see structures below the stratum corneum. The requirement of a liquid interface and direct skin contact can be eliminated with the use of polarized light and a cross-polarizing filter, as utilized in polarized dermoscopes. Although both NPD and PD allow the observer to visualize similar structures below the stratum corneum, subtle differences do exist. These differences tend to provide complementary information.


Nonpolarized dermoscopy works best for visualizing:





 


Polarized dermoscopy works best for visualizing:






Principles of Dermoscopy


The colors seen on dermoscopy, which are based on the depth of the melanin and other skin structures, are illustrated in Figure 32-2.




Network Patterns



Pigment Network


A reticulated pigment network (Figure 32-3) has the following characteristics:







A typical pigment network in a benign nevus consists of (Figure 32-4):






For an atypical pigment network (Figure 32-5),







A pseudonetwork (Figure 32-6) is






A negative network is a reverse network that is seen in melanoma (Figures 32-7 and 32-8). It consists of dark, elongated, and curved globular structures surrounded by relative hypopigmentation. This results in the impression that the lines of the network appear lighter in color with an almost serpiginous pattern with holes that are darker in color (and appear sausage shaped).





Other Structures






Mar 12, 2016 | Posted by in General Surgery | Comments Off on Dermoscopy
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