4 курс / Дерматовенерология / Дерматоскопия (3)

252 Clues and Clichés

References

1Piliouras P, Allison S, Rosendahl C, Buettner PG, Weedon

D.Dermoscopy improves diagnosis of tinea nigra: a study of 50 cases. Australas J Dermatol. 2011; 52(3): 191–194.

2Rosendahl C, Cameron A, Argenziano G, Zalaudek I, Tschandl P, Kittler H. Dermoscopy of squamous cell carcinoma and keratoacanthoma. Arch Dermatol. 2012; 148(12): 1386–1392.

3Selmer J, Skov T, Spelman L, Weedon D. SCCs and KAs are biologically distinct and can be diagnosed by light microscopy. Histopathology. 2016; 69(4): 535–41.

4Marghoob AA, Cowell L, Kopf AW, Scope A. Observation of chrysalis structures with polarized dermoscopy. Arch Dermatol. 2009; 145(5): 618.

5Tschandl P, Rosendahl C, Kittler H. Dermatoscopy of flat pigmented facial lesions. J Eur Acad Dermatol Venereol. 2015; 29(1): 120–127.

6Lozzi GP, Piccolo D, Micantonio T, Altamura D, Peris

K.Early melanomas dermoscopically characterized by reticular depigmentation. Arch Dermatol. 2007; 143(6): 808–809.

7Pizzichetta MA, Talamini R, Marghoob AA, et al. Negative pigment network: an additional dermoscopic feature for the diagnosis of melanoma. J Am Acad Dermatol. 2013; 68(4): 552–559.

8Pizzichetta MA, Canzonieri V, Soyer PH, Rubegni P, Talamini R, Massone C. Negative pigment network and shiny white streaks: a dermoscopic-pathological correlation study. Am J Dermatopathol. 2014; 36(5): 433–438.

9Braun RP, Scope A, Marghoob AA. The “blink sign” in dermoscopy. Arch Dermatol. 2011; 147(4): 520.

10Botella-Estrada R, Requena C, Traves V, Nagore E, Guillen C. Chrysalis and negative pigment network in Spitz nevi. Am J Dermatopathol. 2012; 34(2): 188–191.

11Moscarella E, Lallas A, Kyrgidis A, et al. Clinical and dermoscopic features of atypical Spitz tumors: A multicenter, retrospective, case-control study. J Am Acad Dermatol. 2015; 73(5): 777–784.

12Balagula Y, Braun RP, Rabinovitz HS, et al. The significance of crystalline/chrysalis structures in the diagnosis of melanocytic and nonmelanocytic lesions. J Am Acad Dermatol. 2012; 67(2): 194 e191–198.

13Keir J. Dermatoscopic features of cutaneous non-facial non-acral lentiginous growth pattern melanomas. Dermatol Pract Concept. 2014; 4(1): 77–82.

14Jaimes N, Marghoob AA, Rabinovitz H, et al. Clinical and dermoscopic characteristics of melanomas on nonfacial chronically sun-damaged skin. J Am Acad Dermatol. 2015; 72(6): 1027–1035.

15Lallas A, Tschandl P, Kyrgidis A, et al. Dermoscopic clues to differentiate facial lentigo maligna from pigmented actinic keratosis. Br J Dermatol. 2016; 174(5): 1079–1085.

16Slutsky JB, Marghoob AA. The zig-zag pattern of lentigo maligna. Arch Dermatol. 2010; 146(12): 1444.

17Tschandl P, Rosendahl C, Kittler H. Accuracy of the first step of the dermatoscopic 2-step algorithm for pigmented skin lesions. Dermatol Pract Concept. 2012; 2(3): 203a208.

18Lallas A, Kyrgidis A, Koga H, et al. The BRAAFF checklist: a new dermoscopic algorithm for diagnosing acral melanoma. Br J Dermatol. 2015; 173(4): 1041–1049.

19Tschandl P. Dermatoscopic pattern of a spiradenoma. Dermatol Pract Concept. 2012; 2(4): 204a209.

20Salerni G, Gonzalez R, Alonso C. Dermatoscopic pattern of digital mucous cyst: report of three cases. Dermatol Pract Concept. 2014; 4(4): 65–67.

21Rudnicka L, Olszewska M, Rakowska A, Slowinska M. Trichoscopy update 2011. J Dermatol Case Rep. 2011; 5(4): 82–88.

8.1 Nails

Pigmentations of the nail plate are frequently – probably too frequently – biopsied in order to exclude a melanoma of the nail matrix. However, the decision to biopsy nail pigmentation should not be made lightly – biopsies of the nail matrix are not only painful, they also may cause irreversible abnormalities of nail growth. By keeping a few basic principles in mind, the number of biopsies can be reduced without increasing the risk of missing a melanoma.

In principle, melanomas may occur anywhere in the nail unit, but in practice almost all originate in the nail matrix. Nail matrix pigmented neoplasms create longitudinal pigmentation of the nail plate, known as longitudinal melanonychia. Melanomas that do not arise in the nail matrix but in the nail bed do not produce longitudinal melanonychia. Initially the nail changes produced by nail bed melanoma may be mistaken for “nail dystrophy” or “onychomycosis” and thus remain unrecognized. Fortunately these are exceedingly rare neoplasms.

The following applies exclusively to melanomas that arise from the nail matrix.

Anatomy of the nail

In order to understand nail pigmentation, one must understand the anatomy of the nail organ. The nail plate is a convex 0.5-mm-thick plate composed of keratin. It is the final product of keratinocytes in the nail matrix. The nail plate lies on the nail bed. Its lateral margins are surrounded by the lateral nail fold while its proximal end is spanned by the proximal nail fold. These margins are also known as the nail wall or the paronychium. The narrow cornified portion of proximal nail fold which glides on 1 to 2 mm of the nail plate is known as the cuticle. The nail matrix itself lies below the lunula, the white arc at the proximal end of the nail plate (8.1).

Figure 8.1: Anatomy of the nail plate.

(Adapted from Ackerman and Boer, Histologic diagnosis of inflammatory skin diseases. An algorithmic method based on pattern analysis, 3rd edition).

Dermatoscopy of nail pigmentation

Dermatoscopy of the nail plate requires a high viscosity (“stiff”) contact fluid like ultrasound gel. Thinner fluids like paraffin oil and alcohol do not stay in place due to the highly irregular contour of the nail organ. A contact fluid also improves visualization when performing dermatoscopy with polarized light (1–4).

The most commonly seen pattern on dermatoscopy is a parallel pattern of lines (8.2). In longitudinal melanonychia, these parallel lines extend continuously from the lunula to the free end of the nail plate. Longitudinal melanonychia usually occupies just a part, and less frequently the entire width, of the nail plate. It is attributable to the increased production of melanin in the nail matrix, which may or may not be caused by a proliferation of melanocytes.

Gray pigmentation of lines is usually attributable to an increase of melanin, but it is not associated with proliferation of melanocytes in the nail matrix. The most common causes of gray parallel lines are lentigines (melanotic macules) of the nail matrix, ethnic hyperpigmentation, drug induced hyperpigmentation, hyperpigmentation during pregnancy, and traumatic or inflammatory hyperpigmentation (4). Traumatic hyperpigmentation occurs on finger nails mainly due to manipulation of the nail

organ (so-called onychotillomania, 8.2 middle, right), whereas on the toe nails it primarily occurs due to friction. Friction induced pigmentation of the toe can sometimes show a mix of brown and gray lines and then it is difficult to differentiate this condition from melanocytic lesions (8.2, bottom left). The brown lines caused by trauma are created by a mixture of hemorrhage and post-inflammatory hyperpigmentation. In some of these cases a biopsy is unavoidable.

Gray parallel lines are seen in many inflammatory conditions; for instance, onychomycosis (dermatophytes and even Candida albicans may produce melanin), lichen planus and (more rarely) psoriasis. Rare causes of gray parallel lines are the Laugier-Hunziker syndrome, Addison’s disease or HIV disease (1). Drugs (e.g. tetracycline, AZT, amiodarone) and radiotherapy may also cause gray pigmentation of the nail plate. In all of these conditions, more than one nail is nearly always involved.

Brown or black parallel lines are usually caused by proliferation of melanocytes in the nail matrix. This indicates the presence of a nevus or a melanoma. In cases of nevus, the lines are (approximately) the same color and width, equally spaced, and arranged in a strictly parallel manner (8.2, top). In cases of melanoma, however, they are “chaotic”, which means that they vary in color and width, the distance between the lines varies (8.2 bottom right, 8.3), and the lines are no longer all parallel (4).

The so-called Hutchinson’s sign is defined as a macroscopically visible pigmentation of the proximal or lateral nail fold while the micro-Hutchinson sign refers to pigmentation of the cuticle (8.4). These are both

Figure 8.3: Melanoma of the nail plate.

This melanoma of the nail plate is more advanced than those shown in figure 8.2 bottom right and in figure 8.4. Apart from pigmentation of the nail plate one can see delicate pigmentation of periungual skin (Hutchinson’s sign). The parallel lines of the nail plate vary in color and thickness. Note that there are blood spots, which show that a single criterion can be misleading if the context is ignored. This is a pattern of a melanoma and the unusual finding of blood spots should not alter your diagnosis.

clues to melanoma. The Hutchinson sign and the micro-Hutchinson sign must not be confused with the pseudo-Hutchinson sign (8.5). The pseudo-Hutchinson sign occurs when pigmentation of the nail plate is visible through the cuticle. The pseudo­-Hutchinson sign is not a clue to melanoma.

Melanoma in the nail matrix usually is found on the big toe, thumb or index finger; other digits are rarely affected. As a rule, melanomas of the nail matrix do

not occur in children (5). The exceptional reports of melanoma of the nail matrix in prepubescent children are most probably congenital nevi that have been misdiagnosed as melanomas. Congenital nevi of the nail matrix (which may not be visible at birth) commonly show clues to melanoma including signs of growth. In growing lesions the pigmentation is broader in the proximal part of the nail plate and smaller in the distal part (8.6). While this feature would be regarded as a clue to malignancy in adults one should not be too concerned if it occurs in children. Usually this sign of growth will disappear if the lesion is monitored for some months.

Therefore, even if clues to malignancy are present, biopsy of the nail matrix in prepubertal children should be performed very rarely, and only after careful consideration.

Apart from parallel lines, nail pigmentation may also be seen as dots, clods or a structureless pattern. These patterns occur in isolation or in combination with parallel lines. In most cases dots, clods and structureless areas are a sign of bleeding and therefore not caused by melanin but by hemoglobin (8.7). The distinction between hemorrhage and pigmentation of the nail due to melanin is usually made quite easily. Hemorrhage tends to be red or purple and the pigmentation appears structureless. Pigmentation of the nail plate caused by melanin is usually brown or occasionally black, and usually seen as longitudinal melanonychia, i.e. parallel lines extending the whole length of the nail plate. Parallel lines may also be found in hemorrhage, but not only will they be a different color, the lines do not extend continuously from the proximal to the free distal end of the nail plate. Growth of the nail plate causes pigmentation to advance distally. Pigmentation from hemorrhage advances very slowly; in toe nails it may be as little as 1 mm per month. Over time, a growing, non-pigmented healthy piece of nail will be found between the pigmentation and the proximal nail fold. The pigmentation produced by hemorrhage normally resolves spontaneously, regardless of the pattern seen. Renewed bleeding may occur in case of repetitive trauma and prevent complete outgrowth of the pigmentation. This is especially true for toe nails; at this site the trauma tends to remain unnoticed.

Because neoplasms may bleed, signs of hemorrhage do not entirely rule out a malignancy of the nail unit (8.3). For this reason it is advisable to perform a fol- low-up examination after three months in patients with subungual hemorrhage who are unable to recall an explicit incident of trauma.

Fungal infections may be accompanied by a structureless brown discoloration of the nail; in very rare cases there may also be parallel lines (8.8). This brown pigmentation is due to the fact that fungi may produce melanin. Usually there are additional clues to fungal infections such as thickening of the nail, subungual hyperkeratoses and whitish discoloration of the nail, which usually extends from proximal to distal. Sometimes fungal microscopy or culture may be the only way to establish the diagnosis. There are also pigment-forming bacteria like for example Pseudomonas aeruginosa (8.9), which is characterized by green discoloration of the nail plate (chloronychia).

Rarely, melanomas of the nail organ do not produce longitudinal melanonychia. Melanomas of the nail bed and nail fold may produce other patterns of pigmentation, and amelanotic melanomas are of course non-pigmented. Dermatoscopy features of these rare situations have not yet been described, and diagnosis must be based on clinical features.

Biopsies of the nail matrix

Longitudinal melanonychia originates in the nail matrix, which means any biopsy must be performed not from the nail bed, but from the matrix, at the proximal end of the pigmentation. Dermatoscopy of the free end of the nail helps to identify the zone of the matrix that is responsible for the pigmentation of the nail plate (6). When the pigmentation is mainly in the deeper layers of the nail plate, the biopsy should be performed in the distal part of the nail matrix. Pigmentation in the more superficial layers of the nail plate requires a biopsy from the proximal part of the matrix. These biopsies from the proximal nail matrix are associated with a higher risk of disrupted nail growth.

In narrow lesions (less than 3 mm in diameter) biopsy can be performed by punch excision. In these cases it will be adequate to insert the punch through the nail plate into the nail matrix after folding back the proximal portion of the nail fold. For slightly larger lesions (3 to 6 mm) located in the center of the nail, biopsy can be by transverse excision or shave of the nail matrix, ideally including the entire lesion (1).

For this purpose the nail plate is fenestrated and the nail matrix exposed.

In lesions larger than 6 mm diameter, usually one is only able to perform a partial biopsy – in most cases a punch biopsy – to confirm the diagnosis. Partial biopsies have a major disadvantage, as they make the already demanding histological investigation even more difficult. False negative histopathology reports due to inadequate partial biopsies are not rare.