32 Dermoscopy

Ashfaq A. Marghoob, MD, and Richard P. Usatine, MD

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.¹^–³ 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:

• Allows the observer to concentrate on a lesion and formulate a logical differential diagnosis.

• Helps differentiate melanocytic from nonmelanocytic lesions.

• Helps differentiate benign from malignant lesions.

• Improves diagnostic accuracy.

• Increases the observer’s confidence in his or her clinical diagnosis.

• Confirms naked-eye diagnosis (clinical-dermoscopy correlation).

• Improves malignant-to-benign biopsy ratio (hence, avoiding unnecessary biopsies).

• Helps isolate suspicious foci within lesions, allowing the clinician to give specific suggestions to the dermatopathologist for processing.

• Helps more precisely define borders of some lesions for improved presurgical margin mapping.

• Helps to reassure patients.⁶

• Helps in the surveillance of patients with many nevi.⁶

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.

Figure 32-1 (A) Nonpolarized contact dermoscopes from Heine and Welch Allyn. (B) An assortment of polarized and hybrid dermoscopes from 3Gen.

(A: Courtesy of Heine, Herrsching, Germany, and Welch Allyn, Skaneateles Falls, NY; B: Courtesy of 3Gen, San Juan Capistrano, CA.)

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:

• Milia-like cysts

• Peppering due to regression

• Blue-white colors due to orthokeratosis of the stratum corneum.

Polarized dermoscopy works best for visualizing:

• Shiny white streaks (chrysalis structures) due to altered collagen

• Blood vessels

• Red-pink colors due to increased vascular volume.

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.

Figure 32-2 Colors seen on dermoscopy based on the depth of the melanin and other skin structures.

(Courtesy of Alfred W. Kopf, MD.)

Network Patterns

Pigment Network

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

• The grid-like (honeycomb) network is composed of pigmented lines and hypopigmented “holes.”

• Network lines correspond to the rete ridge pattern of the epidermis.

• Network lines are visible due to melanin pigment in keratinocytes and melanocytes along the dermal/epidermal junction.

• The “holes” correspond to tips of the dermal papillae/suprapapillary plate.

Figure 32-3 Pigment network is created by melanocytes along the rete ridge seen from the skin surface producing a net-like (reticulated) pattern.

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

• A relatively uniform line thickness and color

• A regularly meshed network

• Thinning (fading) at the periphery.

Figure 32-4 Typical pigment network (in a benign nevus). Note the regular line thickness and the fading of the lines at the periphery.

(Copyright Ashfaq A. Marghoob, MD.)

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

• The lines of the network are not uniform in thickness and color.

• The lines are darker and/or broadened compared to a typical network.

• The “holes” are heterogeneous in size.

• The lines end abruptly at the periphery.

Figure 32-5 Atypical pigment network in a dysplastic nevus with variations in line thickness, darkness, and pattern.

(Copyright Richard P. Usatine, MD.)

A pseudonetwork (Figure 32-6) is

• Usually seen in pigmented lesions located on the face.

• Results when the rete ridge pattern is attenuated.

• Has adnexal openings (hair follicles and sweat glands) that form the holes of the pseudonetwork.

Figure 32-6 Pseudonetwork is the net-like pattern made by lightly-colored adnexal openings within pigmented lesions on the face. This is a solar lentigo with a typical moth-eaten border showing the adnexal openings within the pigmented lentigo.

(Copyright Ashfaq A. Marghoob, MD.)

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).

Figure 32-7 Negative network (reverse network) in a microinvasive melanoma. The negative network consists of dark, elongated, and curved globular structures surrounded by relative hypopigmentation.

(Copyright Ashfaq A. Marghoob, MD.)

Figure 32-8 Negative network is created by large nests of melanocytes squeezing the rete ridges, making them into the lighter areas between the darker nests.

Other Structures

Dots

• Dots are small, round structures with a diameter of less than 0.1 mm.

• They are black, brown, blue-gray, or red in color.

• Black dots represent pigment in the stratum corneum.

• Brown dots represent small nevomelanocytic nests at the tips of the rete ridges, at the dermal/epidermal junction, or in the epidermis.

• Blue-gray dots represent free melanin in dermis or in macrophages.

• Red dots represent blood vessels.

Typical dots in benign melanocytic lesions are seen in Figure 32-11. Brown dots on the network appear in normal nevi (Figure 32-12). Brown dots off the network may appear in dysplastic nevi or melanoma (Figure 32-13).

Figure 32-11 Typical dots in benign melanocytic lesions are seen on the pigment network and are caused by a cluster of melanocytes at the base of the rete ridge.

Figure 32-12 Dermoscopy of benign nevus with typical dots on the network.

(Copyright Ashfaq A. Marghoob, MD.)

Figure 32-13 Invasive melanoma with atypical dots near the left edge and atypical globules in the upper left corner.

(Copyright Ashfaq A. Marghoob, MD.)

Globules

• Globules are symmetrical, round to oval structures that are larger than 0.1 mm (Figures 32-13 and 32-14).

• They are brown, black, blue, or red in color.

• Brown, black, and blue globules correspond to nests of pigmented melanocytes at the dermal/epidermal junction or in the dermis.

• Red globules represent blood vessels of neovascularization.

Figure 32-14 (A) Typical globules evenly distributed in a benign nevus. AM. (B) Atypical globules aggregated in the lower left corner of this dysplastic nevus.

(Copyright Ashfaq A. Marghoob, MD.)

Figure 32-14A shows typical globules evenly distributed in a benign nevus; Figure 32-14B shows atypical globules aggregated in the lower left corner of a dysplastic nevus.