Acquired longitudinal melanonychia after puberty in a whiteskinned individual requires urgent biopsy

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Approximately 2-3% of melanomas in whites, and 15-20% in blacks are located in the nail unit. However, malignant melanoma is rare in black people; thus the number of nail melanomas does not significantly differ between these population groups. Most white patients have a fair complexion, light hair, and blue or hazel eyes. There is no sex predominance, although some reports show variable female or male predominance. The mean age at onset is 55-60 years. Most tumours are found in the thumbs or great toes.

Melanoma of the nail region is often asymptomatic. Many patients only notice a pigmented lesion after trauma to the area; only approximately two-thirds seek medical advice because of the appearance of the lesion; pain or discomfort is rare, and nail deformity, spontaneous ulceration, sudden change in colour, bleeding or tumour mass breaking through the nail are even more infrequent. It is useful to remember that a pigmented subungual lesion is more likely to be malignant than benign. If the melanoma is pigmented it may show one or more of the following characteristics:

1 A spot appearing in the matrix, nail bed or plate. This may vary in colour from brown to black; it may be homogeneous or irregular, and is seldom painful.

2 A longitudinal brown to black band of variable width running through the whole visible nail.

3 Less frequently, Hutchinson's sign—periungual extension of brown-black pigmentation from LM onto the proximal and lateral nail folds—is an important indicator of subungual melanoma (but note the reservations discussed below).

Current experience has demonstrated that Hutchinson's sign, while valuable, is not an infallible predictor of melanoma, for the following reasons:

• Periungual pigmentation is present in a variety of benign disorders and, under these circumstances, may lead to overdiagnosis of subungual melanoma.

• Periungual hyperpigmentation occurs in at least one non-melanoma skin cancer: Bowen's disease of the nail unit.

• Hyperpigmentation of the nail bed and matrix may reflect through the 'transparent' nail folds, simulating Hutchinson's sign ('pseudo-Hutchinson's sign'). Each of the above may incorrectly suggest a diagnosis of subungual melanoma. Table 5.6 lists disorders in which pseudo-Hutchinson's sign occurs.

Total reliance on the (apparent) presence or absence of periungual pigmentation may lead to over- or underdiagnosis of subungual melanoma. All relevant clinical and historical information, including the presence or absence of periungual pigmentation, must be carefully evaluated in a patient suspected of having subungual melanoma. Ultimately, the diagnosis of subungual melanoma is made histologically. Hutchinson's sign is a single, important clue to this diagnosis. The nail plate may also become thickened or fissured and permanently shed.

Approximately 25% of melanomas are amelanotic (pigmentation not an obvious or prominent sign; Figure 5.36) and may mimic pyogenic granuloma, granulation tissue or ingrowing nail. The risk of misdiagnosis is particularly high in these cases.

Malignant melanoma must be considered in the differential diagnosis (see Table 5.3) in all cases of inexplicable chronic paronychia, whether painful or not, in torpid granulomatous ulceration of the proximal nail fold and in pseudoverrucous keratotic lesions of the nail bed and lateral nail groove. Subungual melanoma may also simulate mycobacterial infections, mycotic onychodystrophy, recalcitrant paronychia and ingrowing nail. Subungual haematoma is not rare and may present

Table 5.6 Disorders accompanied by pseudo-Hutchinson's sign_

Disorder_Clinical ^ features_

Benign

Illusory pigmentation Dark colour is visible because of the cuticle and thin nail fold transparency and not because of melanin localization within these tissues Proximal nail fold of dark-skinned persons—lateral nail folds not involved; LM may be present or absent; often exaggerated in thumbs May recur after surgical removal Macular pigmentation of lips, mouth and genitalia; one or several fingers involved Hyperpigmentation of fingers and toes, macular pigmentation of buccal mucosa and lips Diffuse tanning of both exposed and non-exposed portions of the body; bluish-black discoloration of the mucous membranes of the lips and mouth Treatment for finger dermatitis, psoriasis and chronic paronychia

Polydactylous involvement Polydactylous involvement Polydactylous involvement; zidovudine produces similar features

Due to friction, nail biting and picking, or boxing Pigment recurrence after biopsy of LM in acquired and congenital melanocytic naevi, often striking cytologic atypia

Monodactylous; initial increase in dyschromia followed by subsequent pigment regression;

Ethnic pigmentation

Naevoid lentigo

Laugier-Hunziker-Baran syndrome

Peutz-Jeghers syndrome Addison's disease

X-ray therapy

Malnutrition Minocycline AIDS patients

Trauma

Congenital or acquired naevus after biopsy

Regressing naevoid melanosis in childhood perplexing disorder Subungual haematoma Exceptionally, blood spreads to nail folds and the hyponychial area

Silver nitrate For treatment of granulation tissue; may produce a black halo

Malignant

Bowen's disease_Features clinically typical of subungual melanoma

(After Baran and Kichijian (1996). LM, longitudinal melanonychia.

Resultados Papanicolau

Figure 5.36

(a, b) Malignant melanoma—amelanotic.

Figure 5.36

(a, b) Malignant melanoma—amelanotic.

without a history of severe trauma. It may follow repeated minor trauma which escapes the patient's attention, such as in 'tennis toe', or follow trauma from wearing hard ski boots. Although haematoma following a single traumatic event usually grows out in one piece, rather than as a longitudinal streak due to the continuous production of pigment, repeated trauma may cause difficulties in differential diagnosis. It is recommended that the lesion should be examined with a magnifying loupe after it has been covered with a drop of oil. The pigmented nail should be clipped and tested with the argentaffin reaction in order to rule out melanin pigmentation. Subungual haemoglobin is not degraded to haemosiderin and is therefore negative to staining with Prussian blue. Scrapings or small pieces of the nail boiled with water in a test tube give a positive benzidine reaction with the conventional haemoglobin reagent strips. The difference between haemosiderinic and melanotic pigment, sometimes difficult to discern by routine histological methods, is easily seen by ultrastructural techniques: ferrous pigment is intercellular while melanin is intracellular.

Because of its frequency, melanonychia striata in people with deeply pigmented skin is considered a normal finding, but up to one-fifth of all melanomas in black patients are in the subungual area, and these typically begin with a pigmented spot producing a longitudinal streak. These spots are usually black rather than the normal brown. The diagnosis may be aided by comparing them with the brown stripes in other nails or by the occurrence of Hutchinson's sign.

The following guidelines should be adhered to where possible to enable accurate tissue diagnosis to be made and appropriate treatment carried out. As a first step, the anatomical site of the matrix affected will be obtained from the level of the melanin pigment identified with Fontana's silver stain of a nail clipping obtained from the distal free edge. The type of biopsy selected will then depend on the site of the matrix melanin production, the width of the linear pigmentation, and the site of the band in the nail plate. If the pigment is located within the ventral portion of the nail plate, a decision has to be made depending on the width of the band:

• A punch biopsy should be used when the width of the band is less than 3 mm. If the base of the nail plate is removed, the specimen may be released more easily, and the integrity of the region distal to the biopsied matrix area may be checked.

• A transverse matrix biopsy should be used for a band wider than 3 mm.

If the pigment involves the upper portion of the nail, it is obviously difficult to use the two previous procedures to remove the source of melanin pigment, for anatomical reasons and because of the risk of a secondary dystrophy, thus:

• A rectangular block of tissue is excised using two parallel incisions down to the bone. An L-shaped incision is carried back along the lateral nail wall, freeing this flap. The lateral section may then be rotated medially and approximated to the remaining nail segment.

• If the band is wider than 6 mm or if the whole thickness of the nail is involved by the pigment, surgical removal of the nail apparatus seems the most logical method. However, one (or even two) 3 mm punch biopsy is an alternative prior to more radical treatment, especially in young women.

• When the band lies within the lateral third of the nail plate, lateral longitudinal biopsy is more suitable.

• If LM is accompanied by periungual pigmentation (Hutchinson's sign), removal of the nail apparatus is required. Histological examination of acral lentiginous melanoma requires great experience, and often serial sections are needed to classify the lesion accurately. Grading according to Clark's levels or Breslow's maximum tumour thickness is difficult and often inconclusive.

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