White : Diseases of the Skin - Disorders of Nails

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Gary M. White & Neil H. Cox

Diseases of the Skin

29	Disorders Of Nails

PIGMENTATION

Longitudinal melanonychia

Etiology and pathogenesis

A longitudinal, pigmented streak of the nail is called longitudinal melanonychia. In one study, the most frequent location was the thumb, followed by the great toe and index finger. They are a common normal variant in people with colored skin.

A nevus or melanocytic hyperplasia of the matrix is the usual cause, but an atypical nevus or a melanoma must be excluded.

Clinical

A longitudinal, pigmented streak of the nail is seen (Figs 29.42 and 29.43). The underlying cause determines the subtleties of its appearance.

Figure 29.42 Longitudinal melanonychia. A brown band in a child.

Figure 29.43 A dark band representing melanoma in situ.

Differential diagnosis

See Table 29.4 for differential diagnosis of pigmentation of the nail.

Table 29.4 DIFFERENTIAL DIAGNOSIS OF PIGMENTATION OF THE NAIL

Type of cause	Example(s)	Comments
Melanocytic lesions	Nevus, melanocytic hyperplasia, melanoma	All cause longitudinal melanonychia.May be normal racial variant (usually multiple bands) in African American, Latino, and Asian patients, especially those over 60 years of age.
Infection	Pseudomonas under area of onycholysis, fungal infection	See text of this chapter for Pseudomonas ; rare in fungal infection, andaccompanied by subungual thickening.
Friction or traumatic	Subungual hematoma, skier's or footballer's toe	See text, this chapter. /td>
Drugs	Minocycline, zidovudine, busulfan, cyclophosphamide, hydroxyurea	Zidovudine and cytotoxics usually cause longitudinal melanonychia that may have delayed onset (e.g. typically 6–24 months from the start of hydroxyurea therapy); minocycline pigmentation is bluish and proximal or diffuse.
Neoplasia	Bowen disease, basal cell carcinoma	Bowen disease may cause longitudinal melanonychia.
Endocrine	Addison disease	Usually with associated intraoral pigmentation.
Idiopathic	Laugier–Hunziker syndrome	With blotchy pigmented spots of lips or oral mucosa, and may affect acral skin also.

Treatment

The cause of the pigmentation determines the treatment. Clinical judgment should be based on a variety of factors. For example, a wide, dark, solitary band in an older person should be biopsied, whereas multiple, narrow, uniformly colored bands in a darkly skinned young person are likely to be benign. It has been recommended that a wait and see policy in prepubertal children with stable congenital or acquired longitudinal melanonychia be entertained. Pigmentation of the periungual skin ( Hutchinson sign) is particularly worrisome. Of note, the pseudo-Hutchinson sign is a benign pigmented streak visible through a thin proximal nail fold (see earlier text in discussion of subungual hematoma).

To biopsy, retract the proximal nail fold after making a longitudinal incision and biopsy the origin of the streak.

It cannot be emphasized enough that any melanocytic proliferation of the nail matrix that results in an unusual pigmented band should be biopsied appropriately to exclude melanoma.

PRACTICE POINTS

•	The pigmentation that is worrisome for melanoma extends back to the nail matrix. The acute appearance of pigmentation under the nail, unconnected to the proximal nail fold or lunula, usually represents a hematoma.
•	A biopsy to diagnose the cause of longitudinal melanonychia must be from the origin of the streak under the proximal nail fold; biopsy of the nail plate more distally will just show some increased pigmentation.
•	Benign causes of longitudinal melanonychia are usually constant, so the band has parallel edges; by contrast, an enlarging proximal melanoma may cause a band that diverges from the free edge of the nail toward the proximal nail fold.

Laugier–Hunziker syndrome

The Laugier–Hunziker syndrome combines pigmented bands of the nails with lentigines of the oral mucosa (Fig. 29.44). For more discussion, see Chapter 20 ( Oral and genital disorders ).

Figure 29.44 Laugier–Hunziker syndrome combines pigmented bands of the nails with lentigines of the oral mucosa. Occasionally, pigmented macules of the fingertips, as shown here, are present as well. Pigmented bands and macules on multiple digits would imply Laugier–Hunziker syndrome, as was true in this case. If this pigmentary change had occurred in isolation, however, a biopsy would be indicated.

Drug-induced nail pigmentation

Pigmentation of the nail may occur with the administration of various drugs, including AZT, cyclophosphamide, hydroxyurea, bleomycin, doxorubicin, fluorouracil, methotrexate, and melphalan. Transverse bands (thought to correspond to administration of the cytotoxic agent), longitudinal bands, and rarely diffuse pigmentation may occur. Some of these drugs may cause skin or mucosal pigmentation as well (Fig. 29.45).

Figure 29.45 Various drugs, including minocycline, AZT, and the antimalarials, may cause pigmentation of the nail. This case was secondary to external contact with hydroquinone.

Leukonychia

The commonest forms of leukonychia are listed below, the punctuate type being much the commonest.

•	Congenital leukonychia (Fig.29.46). This occurs rarely. The familial type usually shows autosomal dominant inheritance, and a gene defect in chromosome 12q13 has been found. As the type II keratins map within this chromosomal interval, it is possible that a mutation in one of these keratin genes may be a cause of hereditary leukonychia. In the inherited types, most or all of the nail is white (Fig.29.47). There is no treatment.
•	Punctuate leukonychia—this type (Fig.29.48) is due to minor unnoticed trauma.
•	Striate leukonychia—horizontal white bands. One acquired type has been called Mee lines and classically develops after exposure to arsenic, although other nail matrix poisons such as chemotherapeutic drugs cause exactly the same picture.
•	Pallor of nails (less overtly white than in the hereditary leukonychias already discussed) is associated with hypoalbuminemia, anemia, and hepatic or renal failure.
•	Longitudinal leukonychia occurs in Darier disease.

Figure 29.46 Congenital leukonychia.

Figure 29.47 Congenital leukonychia. Each nail exhibits partial to near-complete leukonychia in this inherited case.

Figure 29.48 Acquired leukonychia: punctuate type, associated with trauma. These white spots on the nail are extremely common.