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Nail abnormalities are commonly an isolated benign finding related to infection or trauma. Occasionally, a nail change is a manifestation of an underlying generalized skin disorder, a systemic disease, or a congenital syndrome. Nail problems are often difficult to diagnose and are notoriously difficult to treat. Most diagnoses are made clinically. A nail matrix biopsy can also be performed, but the biopsy may itself cause a permanent nail dystrophy.Knowledge of nail anatomy is essential for an understanding of nail disease (see Fig. 356-2). The nail plate is firmly attached to the vascularized, innervated nail bed by two parallel, longitudinal grooves at either side. The cuticle firmly attaches to the proximal nail plate, preventing water, bacteria, and other irritants from entering the area of nail synthesis, the nail matrix. The proximal portion of the nail matrix lies underneath the proximal nail fold, 2 to 3 millimeters proximal to the cuticle. 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.

Oncycholysis is separation of the nail plate from the nail bed. It may be caused by trauma, psoriasis, certain medications, and fungal or yeast infections (eFig. 366.1). Fungal infection (onychomycosis) may occasionally cause onycholysis without concomitant subungual debris. More commonly, thickening and yellowing of the nail, as well as subungual debris is seen in addition to distal onycholysis. Oral antifungal agents should be deferred until infection is confirmed by culture. When evaluating onycholysis, obtaining a history of trauma, thumb sucking or other chronic wet exposures, medications, and other cutaneous lesions is important. Onycholysis can be seen with retinoids, antineoplastic agents, and valproic acid, as well as after UV exposure (photoonycholysis) with tetracyclines and thiazides. Onycholysis often responds to trimming back the nail, avoidance of frequent contact with water, and use of a topical anticandidal agent.

In koilonychia, affected nails are concave or “spoon shaped” (eFig. 366.2). 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.

Nail pitting (punctate depressions in the nail plate) reflects an abnormality of growth in the proximal nail matrix with imperfect nail plate formation and focal loss of keratin. In children, pitting is usually seen in association with psoriasis (eFig. 366.3), alopecia areata, or eczema. Pits seen in psoriasis are usually randomly distributed, whereas in alopecia areata rows of regularly spaced pits are seen. An ...

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