4 курс / Дерматовенерология / Дерматоскопия (3)

Pigmented Bowen’s disease

Pigmented Bowen’s disease shows two common patterns. The most common is structureless and brown (3.52). Less common, but more specific is an asymmetric combination of brown and/or gray dots (or more rarely small brown clods), and a hypopigmented (pink, white, or skin colored) structureless area. Vessels are coiled and usually seen in hypopigmented zones (3.53). At 10x magnification these vessels may resolve as dots rather than coils. Arrangement of vessels may be linear, random or clustered. A few white clods may be seen, being a dermatoscopic sign of surface scale. The arrangement of brown and/or gray dots as radial lines is an important clue (3.53). Coiled vessels may also be incorporated into these radial lines.

Reticular lines should be absent, their presence being a strong clue to consider an alternative diagnosis. If they are present they usually indicate a collision with solar lentigo. For lesions on lighter skin phototypes, the presence of black pigmentation is also a clue against the diagnosis of pigmented Bowen’s disease. The derma-

toscopic presentation of pigmented Bowen’s disease is the same irrespective of whether it has been induced by UV radiation, chemicals such as arsenic, or, by human papilloma virus (HPV) infection as shown in figure 3.54.

Correlation between dermatoscopy and dermatopathology

The gray dots of pigmented actinic keratoses and Bowen’s disease correspond to melanophages in the papillary dermis. The predominance of the structureless pattern in both lesions indicates the absence of rete ridges (a frequent consequence of heavy UV exposure). The circular arrangement of dots in facial pigmented actinic keratosis is due to the fact that the round openings (infundibula) of hair follicles are non-pigmented and melanophages tend to be arranged around the follicle. The brown dots in pigmented Bowen’s disease correspond to accumulations of melanin in an angiocentric location in the dermal papillae this being the reason red dots in linear array may merge into pigmented dots in the same linear arrangement.

3.7 Characteristic features of melanocytic lesions

3.7.1 Melanocytic nevi Clark nevus

The most common acquired nevus is the Clark nevus. While on dermatoscopy it shows remarkably diverse morphology, there are specific features which distinguish the Clark nevus both from other benign nevi on the one hand and melanoma on the other (3.55–3.59). However the range of appearances of Clark nevi does overlap with both superficial congenital nevi and melanoma (especially in situ melanoma) to an extent that differential diagnosis may be quite difficult even with dermatoscopy. This does not mean that a biological zone of overlap actually exists; rather this should be viewed as a limitation of the method.

The reticular pattern usually predominates in the Clark nevus; indeed most often thin reticular lines is the only pattern (3.55). In the growth phase, the reticular pattern may be combined with peripheral dots or clods (3.56). These peripheral structures usually regress as the nevus matures. Clark nevi consisting solely of brown dots or small brown clods are exceptions. Less common again is the combination of the reticular pattern with a structureless zone, nearly always hyperpigmented and located centrally.

In general – as one expects in benign lesions – combinations of patterns are arranged symmetrically in the Clark nevus. The same is not true for arrangements of colors, which may be symmetrical or asymmetrical. As the proliferation of melanocytes in the epidermis is the essential architectural feature of the Clark nevus, the colors are those of melanin in the epidermis: light-brown, dark-brown and black. The commonest arrangements of colors in the Clark nevus are uniform brown pigmentation, and brown peripherally with central hyperpigmentation. This pattern of central hyperpigmentation of a reticular lesion is a clue to the diagnosis of Clark nevus. Pigmentation may also be variegate, or eccentrically hyperpigmented. This pattern of Clark nevi overlaps morphologically with in situ melanoma.

Other features, especially those of melanoma, are usually absent. Occasionally one finds a few gray dots (melanophages in the dermis), erythema (a sign of inflammation) or peripheral radial lines occupying the whole circumference.

Very rarely there may be skin-colored or white reticular lines. It should be noted that grey dots and white lines are also clues to melanoma. In these rare cases it may not be possible to confidently reach a diagnosis of Clark nevus. In general, pattern and color, and the symmetry of their combinations, should be given

greater importance than any single clue to melanoma. The pattern of vessels in Clark nevi is unremarkable: it usually consists of a pattern of dots occasionally interspersed with short vessels, either straight or curved. Distinguishing between a Clark nevus and a “superficial” or a “superficial and deep” congenital nevus is usually simple. Clark nevi are flat clinically while “superficial” or “superficial and deep” congenital nevi are raised. The reticular pattern is predominant in Clark nevus, the clod pattern is usually (but not always) predominant in congenital nevi. Clark nevi are either uniformly pigmented or marked by central or eccentric hyperpigmentation, while small congenital nevi are usually centrally hypopigmented or variegate (see the section on this entity). Confusion arises because most dermatopathologists do not make this distinction, describing both Clark nevi and small congenital nevi as “dysplastic” junctional or compound nevi or simply as a junctional or compound nevus.

Correlation between dermatoscopy and dermatopathology

The 2-dimensional horizontal projection of the 3-dimen- sional rete ridges causes the characteristic reticular pattern on the surface of the skin. The pigmented lines correspond to vertically arranged rete ridges while the hypopigmented center represents the dermal papillae. The brown pigmentation of lines is primarily due to deposits of melanin in basal keratinocytes. Often the melanocytes themselves are not sufficiently pigmented to be visible on dermatoscopy. If they are, they appear as brown dots or clods that correspond to smaller or larger nests of melanocytes at the dermoepidermal junction.

“Superficial” and “superficial and deep” congenital nevi

Like Clark nevi, “superficial” and “superficial and deep” congenital nevi are extremely diverse morphologically, but have specific clues that usually make diagnosis straightforward. Again, it should be remembered that in this context the term “congenital” does not necessarily mean that the nevus was visible at birth. As mentioned in chapter 2, “superficial” and “superficial and deep” congenital nevi have a different architecture to Clark nevi and are usually easy to distinguish from the latter by histopathology.2 As we have described above, this is also true – with certain limitations – of dermatoscopy. While the reticular pattern is predominant in Clark nevus, the clod pattern is predominant in congenital nevi (3.60, 3.61). The clod pattern occurs either alone

2Regrettably, this distinction is not made by many dermatopathologists. Both types of nevi are termed “dysplastic compound nevi” or “compound nevi”.