Dermoscopy allows the clinician to visualize structures below the level of the stratum corneum. These structures are not routinely discernible without dermoscopy. The presence or absence of specific dermoscopic structures, their location and their distribution can assist the clinician in making a diagnosis or at least in narrowing the differential diagnosis.
The major goal of dermoscopy is to differentiate benign from malignant lesions on the skin so that one is less likely to miss a skin cancer (higher sensitivity) and less likely to perform unnecessary biopsies (higher specificity). Together, this will increase your diagnostic accuracy.
There are 3 major types of dermatoscopes:
Hybrid, which combines a polarized mode with a nonpolarized mode in one dermatoscope.
Because some structures are better seen under polarized light and others best seen without polarization is helpful to purchase a hybrid dermatoscope. Dermatoscopes are currently manufactured by 3Gen, Welch Allyn, Canfield and Heine (Figures C-1 and C-2). A number of dermatoscopes work well while attached to the iPhone for easy image capture and full screen images that can be shown to the patients.
An assortment of polarized and hybrid dermatoscopes from 3Gen. (Courtesy of Richard P. Usatine, MD and 3Gen, San Juan Capistrano, CA.)
Nonpolarized contact dermatoscopes from Heine and Welch-Allyn. (Courtesy of Heine, Herrsching, Germany, and Welch Allyn, Skaneateles Falls, NY.)
Dermoscopic diagnosis is based on the 2-step dermoscopy algorithm described in Figure C-3.
Two-step diagnostic procedure requires separating all lesions into melanocytic or nonmelanocytic as step 1. BCC, Basal cell carcinoma; CCA, clear-cell acanthoma; DF, dermatofibroma; HG, hemangioma; SCC, squamous cell carcinoma; SK, seborrheic keratosis.
Step 1 requires the observer to decide whether the lesion in question is of melanocytic origin (contains melanocytes and therefore could be a melanoma). If the lesion is deemed to be a melanocytic lesion then the observer proceeds to step 2. In this phase of the evaluation, the observer needs to decide whether the lesion is a benign nevus or a melanoma. However, if during step 1 analysis the lesion does not display any features of a melanocytic lesion then the observer needs to decide if the lesion possesses any criteria for a basal cell carcinoma, seborrheic keratosis, hemangioma, or dermatofibroma. If the lesion does not display any structures common to the aforementioned lesions then the lesion is considered nondescript or featureless. The index of suspicion needs to remain high for all featureless lesions as amelanotic melanoma can present as a completely structureless lesion. These featureless lesions sometimes do reveal blood ...