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