4 курс / Дерматовенерология / Дерматоскопия (3)

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As we have seen in previous chapters, clues are important hints that help to solve the differential diagnosis produced by analysis of pattern and color. They usually point towards a diagnosis, but very few clues are specific for a particular diagnosis in all contexts. Studies which state that a particular clue has a given sensitivity and specificity should be interpreted with caution as there is always a selection bias (usually admitted) in the choice of included lesions, the series may not be large, and all too often the clue is only evaluated in a limited context, most commonly of distinguishing nevus from melanoma. Clues must always be interpreted in context, otherwise a good clue may become a cliché. This chapter will look at a selection of clues that deserve special attention, and at some common clichés.

7.1 Clues

Adherent fiber

Adherent fiber is a dermatoscopic clue to ulceration. Ulceration may of course be caused by trauma to normal skin or benign lesions, but malignant neoplasms and especially basal cell carcinomas may ulcerate after trivial irritation. The serum or blood that leaks onto the skin has adhesive properties which persist when it dries out and this may trap fibers of clothing fabric, other exogenous debris or the patient’s own dislodged hair. Adherent fiber may be found on basal cell carcinomas even when ulceration was not observed prior to dermatoscopy. As ulceration is often an important clue to malignancy, so is the presence of dermatoscopically observed adherent fiber (7.1).

Branched fine lines in flat acral lesions

Brown or gray branched fine lines sprinkled with dots in a flat acral lesion is a very distinctive pattern. When uniformly distributed over the whole lesion (7.2), it is pathognomonic for tinea nigra (1). As tinea nigra commonly occurs on the feet where surgery is technically difficult, the diagnosis is best confirmed by a successful trial of treatment with topical antifungal cream. This leads to resolution of the lesion within 3 weeks and avoids a biopsy to exclude melanoma.

Branched serpentine vessels adjacent to keratin

The presence of branched serpentine vessels adjacent to keratin is a strong clue to keratoacanthoma (7.3). Commonly keratoacanthomas are symmetrical lesions with a central keratin plug and vessels (linear, looped, serpentine, coiled or polymorphous) arranged in a radial pattern and with this morphology they are easily identified (2). The clue of branched serpentine vessels adjacent to keratin is particularly useful when the presentation is not typical, but it is also often present in the more typical cases. There is an ongoing controversy among different schools of dermatopathologists whether keratoacanthomas are benign lesions or highly differentiated variants of squamous cell carcinoma (3). However, even the proponents of the concept that a keratoacanthoma is a benign neoplasm agree that lesions that appear as keratoacanthomas clinically or dermatoscopically should be excised to rule out squamous cell carcinoma.

Circles, ovals, and distorted circles

A pattern of circles on non-facial skin, not correlating to infundibulae and in conjunction with ovals and distorted circles is a strong clue to a seborrheic keratosis (7.4). The circles, ovals and distorted circles are produced by elongation and broadening of rete ridges due to acanthosis of the epidermis (7.5). Pigmentation of these structures is due to hyperpigmentation of basal keratinocytes.

Double reticular lines

Occasionally it is apparent on higher magnification that the individual “lines” forming a reticular pattern are actually double lines enclosing a hypopigmented space. The double line corresponds to pigmented basal keratinocytes. The hypopigmented space between the pair of lines indicates that the rete ridges are not filled with pigment. If this pattern is found throughout a lesion

it usually indicates a benign lesion. It usually indicates a junctional Clark nevus (7.6). If, on the other hand, the rete ridges are broadened and filled with pigment (filled with neoplastic melanocytes) the hypopigmented space becomes pigmented and instead of double lines one sees thick reticular lines, which is a clue to melanoma. Occasionally one finds thick reticular lines in a seborrheic keratosis. In this case the rete ridges are not filled with neoplastic melanocytes but with pigmented keratinocytes.

Four dots in a square (four-dot clod)

These structures were first described by Marghoob and Cowell (4) who called them “rosettes” (see also chapter 4). They are only seen with a polarizing dermatoscope (7.7), and are composed of 4 white dots arranged in a square or as a rhomboid. With a non-polarizing dermatoscope, this structure is seen as a simple white