Bowen's disease_Features clinically typical of subungual melanoma
(After Baran and Kichijian (1996). LM, longitudinal melanonychia.
(a, b) Malignant melanoma—amelanotic.
(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.
Was this article helpful?
Complete Guide to Preventing Skin Cancer. We all know enough to fear the name, just as we do the words tumor and malignant. But apart from that, most of us know very little at all about cancer, especially skin cancer in itself. If I were to ask you to tell me about skin cancer right now, what would you say? Apart from the fact that its a cancer on the skin, that is.