Clubbed nails Increased curvature of the nail plate may be due to a wide variety of causes. In this patient, the large, convex nails are a hereditary anomaly and were found to be present in both father and brother. Other causes of clubbing of the nails in children include cyanotic congenital heart disease, cystic fibrosis, and chronic inflammatory bowel disease.

Trachyonychia Any skin disease that affects the nail matrix may result in an abnormal nail plate. There are children, though, who only manifest dystrophy of the nail without any other cutaneous lesions. The nails have a rough, sandpaper-like quality as well as longitudinal ridging and occasional splitting at the distal nail edge. When all nails are involved, the condition that has been termed twenty nail dystrophy of childhood. Similar nail changes can be seen in lichen planus and alopecia areata. In many patients the condition spontaneously regresses.

Traumatic onychodystrophy (Habit tic deformity) Trauma to the nail plate or nail folds can produce a wide variety of nail deformities. The one pictured in Fig. 29-3 is the result of a habit tic. This common nail dystrophy is characterized by a longitudinal canal that runs down the center of the entire nail plate. It is caused by manipulation of the proximal nail fold by the index finger of the same hand.

Dystrophia unguis mediana canaliformis This is a rare condition of unknown etiology that usually involves the thumb. It consists of a canal that runs near the center of the length of the nail plate. Small cracks that extend laterally from the linear canal give the appearance of an inverted fir tree. This deformity tends to resolve spontaneously over a period of months but often recurs.

Leukonychia totalis This is a rare nail disorder that is inherited in autosomal dominant fashion. The color of normal nail plates beyond the lunulae is normally pink from the blood in the blood vessels of the nail bed. The whiteness shown in Fig. 29-5 is due to an abnormality in the nail plate. The nails may also be brittle.

Leukonychia striata The horizontal white streaks pictured in Fig. 29-6 are the result of abnormal keratinization of the nail plate. The tendency toward leukonychia striata is sometimes inherited in an autosomal dominant fashion. In other cases, it can be attributed to vigorous manicuring, to trauma, or to a wide variety of systemic illnesses. In many patients, there is no obvious cause, and the streaks resolve spontaneously.

Onycholysis This word means separation (-lysis) of nails (onycho-) from nail beds. There are many causes for such a development. The commonest are mechanical. Nails worn long are frequently lifted by being snagged. Excessive soaping and soaking in heavy housework promote separation.

Figures 29-7 and 29-8 illustrate onycholysis associated with drug-induced photosensitivity. Figure 29-7 illustrates a reaction to tetracycline, and Fig. 29-8 to doxycycline. Doxycycline, frequently used in the treatment of acne, is a particularly common cause of photosensitivity.

Onychomadesis Figure 29-9 illustrates separation of the nail plate from the matrix with continued attachment to the nail. The process may eventuate in shedding of the nail. Onychomadesis has been associated with infection, and is particularly common after atypical hand-foot-mouth disease (Figs. 5-59 to 5-62). Other causes include pemphigus vulgaris (Figs. 17-1 to 17-4). Oncyhomadesis may occur after chemotherapy or as a side effect of antiepileptic medications.

Onychoschizia This disorder is characterized by lamellar splitting of the nails. It is a form of nail brittleness and is usually the result of practices, such as dish washing, that require repeated wetting and drying of the nails. The problem can sometimes be prevented by the use of plastic or rubber gloves with cotton liners.

Beau lines These transverse lines or furrows begin at the proximal nail fold and grow out with the nail. They represent a brief interference of nail growth secondary to physical stress such as an illness or nutritional deficiency. The lines are not noticed until several weeks after the precipitating event.

Discoloration of nail plates Many chemicals can discolor nail plates. Solutions of potassium permanganate and silver nitrate stain nail plates brown-purple and jet black, respectively. In the case illustrated in Fig. 29-12, the stain is derived from resorcinol. Such stains are harmless and can be easily removed by superficial scaling with the edge of a glass slide.

Nail-patella syndrome This entity, also known as hereditary osteo-onychodysplasia, is a genetic disease linked to a mutation in the gene encoding transcription factor LMX1B, mapped on the long arm of chromosome 9 (9q34).

The manifestations include fingernail dysplasia, absent or hypoplastic patellae, the presence of posterior conical iliac horns, and abnormalities of the radial heads. Patients are also at risk for kidney disease and glaucoma.