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Abnormalities of the nail unit are common in children and usually represent an isolated benign process as opposed to a manifestation of an underlying generalized skin disorder, a systemic disease, or a genetic syndrome. Diagnosis of most common disorders of the nail unit is usually possible on clinical examination. An understanding of the normal anatomy of the nail unit is essential for an understanding of nail disease (see Fig. 351-2).
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The nail plate is a keratinized structure that is attached to the vascularized, innervated nail bed at the lateral nail folds (paronychium), the hyponychium, the proximal nail fold (eponychium), and cuticle. The integrity of the cuticle prevents water, bacteria, and other irritants from entering the nail matrix, which is the area of nail plate synthesis. The lunula, or half-moon, is the visible distal portion of the matrix. Nails grow at an average rate of 0.5 to 1.2 mm/week. The complete replacement of a fingernail takes 6 to 8 months, whereas the replacement of a toenail takes 12 to 18 months.
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Nail dystrophy, or onychodystrophy, is common in children. Onycholysis occurs when there is separation of the nail plate from the nail bed. It is often caused by trauma, thumb or finger sucking, or chronic exposure to water; psoriasis, certain medications, and fungal or yeast infections may also cause onycholysis (Fig. 361-1). Onycholysis is associated with several medications, including systemic retinoids, antineoplastic agents, and valproic acid, and may occur after ultraviolet light exposure (photo-onycholysis) with use of tetracyclines and thiazides. Onycholysis often responds to appropriate nail hygiene with frequent trimming of the nail plate, avoidance of frequent contact with water, and use of a topical antimicrobial agent where indicated. The “oil spots” and “salmon patches” seen in association with psoriasis represent onycholysis involving the central area of the nail bed.
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Koilonychia refers to nails that are concave or “spoon shaped” (Fig. 361-2). Koilonychia may occur as an autosomal dominant trait or in association with iron deficiency, hypothyroidism, hemochromatosis, or lichen planus. Koilonychia may be present as an isolated finding in newborns and young children, especially on the toes, and in those cases improves spontaneously over several years. As such, otherwise healthy children with koilonychia do not usually require further evaluation.
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Nail pitting presents as punctate depressions in the nail plate and reflects an abnormality of the proximal nail matrix that results in irregular nail plate formation and focal loss of keratin. In children, nail pitting is usually seen in association with psoriasis (Fig. 361-3), alopecia areata, or ...