Chapter 366. Disorders of Nails

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 occasional pit may be present as a normal variant. Rarely, multiple pits occur without any apparent skin or hair disease.

Clubbing or acropachy, long recognized as a manifestation of cardiac and pulmonary disease, is defined as a reduction of the obtuse angle between the cuticle and nail bed. In children, congenital cyanotic heart disease, cystic fibrosis, and inflammatory bowel disease are the most frequent causes. Two kinds of hereditary clubbing exist: isolated, familial clubbing and pachydermoperiostosis. The latter is associated with scalp redundancy (cutis vertices gyrata) and thickening of the hands and feet. Racket nails may be confused with true clubbing. The nails are short and broad and are usually found on the thumb and great toes (eFig. 366.3). In contrast to clubbing, the angle formed by the proximal nail fold and nail plate is not altered. The condition may be inherited as an autosomal-dominant trait or associated with Rubenstein-Taybi syndrome, cartilage-hair hypoplasia, and other skeletal dysplasias.

Horizontal ridging is commonly seen with inflammation of the proximal nail fold, as in candidal paronychia or atopic dermatitis. Beau lines are horizontal grooves resulting from abrupt, temporary cessation of nail growth due to a systemic illness or medication (eFig. 366.4). If the insult was brief, the depression is narrow. If the growth arrest lasts several weeks, the depression will be wider. The time of insult can be estimated by the position of the groove along the nail plate. Beau lines may be seen in newborns at around 4 weeks of age. Onychomadesis, similarly, is complete separation of the nail plate due to full matrix arrest secondary to a systemic illness, medication, or other stressor (eFig. 366.5). The nail regrows normally. Longitudinal grooves may result from any process causing inflammation in the nail matrix, including trauma, lichen planus, psoriasis, alopecia areata, Darier disease, Langerhans cell histiocytosis, and graft-versus-host disease. Wide longitudinal grooves may be caused by growths (usually visible) pressing on the matrix, such as large periungual warts, digital mucous cysts, or the periungual fibromas of tuberous sclerosis (eFig. 366.6).

Median nail dystrophy is characterized by a longitudinal groove or fissure in the center of the nail plate, usually the thumbnail. Splits and grooves radiate from the central groove, resembling a fir tree (eFig. 366.7). Habit-tic dystrophy is a similar finding caused by continuous picking or rubbing of the proximal nail fold and cuticle. Unlike median nail dystrophy, the ridges extending from the central depression are horizontal and irregularly spaced. Habit-tic dystrophy improves with cessation of the habit.

Trachyonychia manifests with multiple pits, longitudinal ridging, and a typical sandpaperlike appearance (eFig. 366.8). It can involve one, several, or all finger- and toenails. Twenty nail dystrophy is the term used when most or all digits are involved (eFig. 366.9). It usually develops in children and typically resolves over several years. Trachyonychia can be seen as an isolated finding or in association with psoriasis, lichen planus, alopecia areata, and eczema.1

Onychorrhexis, longitudinal splitting of the nail plate, is seen in brittle nails. Onychoschizia, lamellar splitting of the nail plate at the distal free edge, is usually due to repeated trauma, exposure to nail polish, or frequent immersion in water or other drying solutions.

Pincer nails are characterized by an overcurvature of the lateral aspects of the nail plate and are usually seen as a congenital deformity. Pincer nails do not resolve spontaneously and may become painful, requiring surgical correction.

Acute paronychia, characterized by painful, erythematous swelling of the proximal or lateral nail folds, is usually caused by Staphylococcus aureus infection. Treatment includes incision and drainage with or without antibiotic therapy. Chronic paronychia manifests with erythema, scaling, and edema of the proximal nail fold. Chronic exposure to wet environments or trauma lead to separation of the cuticle from the proximal nail fold, which allows foreign material, water, and other irritants to enter the cleft between the nail plate and the nail fold, causing inflammation. Secondary infection with Candida is often seen. Pressure of the inflamed proximal nail fold on the nail matrix eventually results in grooves on the nail plate. Treatment includes mild topical steroids, topical anticandidal agents, and avoidance of thumb sucking and wet exposure.2,3

Psoriasis may cause pitting, onycholysis with or without subungual debris, nail thickening, leukonychia, and partial or complete nail shedding (eFig. 366.3). It is unusual for all nails to be affected. The presence of papulosquamous lesions on the skin or scalp allows the diagnosis to be made with certainty; however, psoriasis may be limited to the nails. Nail psoriasis is difficult to treat. Steroid injections into the proximal nail fold may be helpful, but are too painful for children. Application of potent topical steroids under occlusion to the proximal nail fold may be of help, but can result in adverse effects, such as atrophy of the nail fold and resorption of the underlying phalanx. Tazarotene gel has been used with some success in small case series.4,5

Lichen planus may cause longitudinal ridging and fissuring, nail thinning, and scarring. Pterygium formation, where the proximal nail fold and cuticle fuse with the nail plate, is an uncommon but characteristic finding in lichen planus. Idiopathic atrophy of the nails may rarely be seen in children with nail lichen planus. It is characterized by an acute and rapid course and results in diffuse, painless, permanent nail destruction.6 Oral leukokeratosis and violaceous, scaly cutaneous papules and plaques are additional manifestations of lichen planus. However, nail lichen planus may be seen without any cutaneous signs of the disease.

Congenital nail abnormalities may occur as isolated defects or part of a more generalized syndrome. Many neonates appear to have ingrown nails distally (pseudo-ingrown toenails of the newborn). This is a common phenomenon that resolves spontaneously during the first year of life. Congenital malalignment of the great toenails is seen in newborns whose nail matrix and the nail plate it produces deviate laterally and do not align with the nail bed (eFig. 366.10). It is self-limited in some infants, but persists in others, in which case surgical intervention is required to prevent chronic ingrowing.7,8

Pachyonychia congenita is transmitted as an autosomal-dominant trait. The nails are thickened and yellow-brown, with an increased curvature and subungual hyperkeratosis (eFig. 366.11). Nail changes may present in the neonatal period. All 20 nails are usually affected. In pachyonychia congenita tarda, a late onset variant, nail changes may not appear until the teenage years or later.9 Associated findings may include palmoplantar keratoderma, hyperkeratotic plaques over the elbows and knees, oral leukokeratosis, natal teeth, and steatocystoma multiplex.

Nail abnormalities associated with ectodermal dysplasias may be obvious at birth or have a later age of onset (eFigs. 366.12 and 366.13). Ectodermal dysplasias are a heterogenous group of inherited defects characterized by impaired development of the skin, hair, and nails. Nail dystrophy is the predominant feature of hidrotic ectodermal dysplasia, or Clouston syndrome, an autosomal-dominant disorder also characterized by hyperkeratosis of the palms and soles and hair defects.

Micronychia (small nails) may be seen in the nail-patella syndrome, inherited as an autosomal-dominant trait. The nail deformities are seen at birth and do not progress. Micronychia is most common on the thumbs and index fingers. Other features include triangular lunulae, absent or hypoplastic patellae, nephrosis, and occasional ophthalmologic and central nervous system abnormalities. Micronychia is also seen after intrauterine exposure to alcohol, warfarin, and phenytoin, as well as in trisomy 8, 13, and 18, and several ectodermal dysplasias. Small, dystrophic, or absent nails are also common in dystrophic and junctional forms of epidermolysis bullosa (eFigs. 366.12 and 366.13).

Nail changes in Darier disease include white and red longitudinal streaks, distal V-shaped notching, and nail thickening. Nail dystrophy is often the first sign of dyskeratosis congenita, an X-linked recessive disorder characterized by reticulated skin dyspigmentation and mucosal leukoplakia. The nail changes are progressive and include splitting, pterygium formation, loss of nails, and scarring of the nail bed.

Discoloration of the nail can be due to staining from an external agent, deposition of pigment within the nail plate, or pigment in the nail bed. Exogenous pigment, such as the yellow staining seen in smokers, typically follows the shape of the cuticle.

Trauma to the nail can lead to the development of a subungual hematoma and subsequent brown-black pigmentation in the nail bed. Chronic trauma or pressure on the toenails may also lead to similar deposition of pigment following hemorrhage within the area. White discoloration (leuconychia) is common. It may be due to changes in the nail plate (true leukonychia) or changes in the underlying nail bed (apparent leukonychia). Transverse or punctate white areas are usually a result of trauma, but may be familial. Half-and-half nails (Lindsey nails) consist of white discoloration of the proximal nail and red coloration of the distal portion, and are seen with uremia. Terry nails, with white discoloration of all but a few millimeters of the distal edge, are associated with cirrhosis or congestive heart failure (eFig. 366.14). Paired horizontal white bands, or Muehrcke lines, are seen with hypoalbuminemia and chemotherapy, whereas Mee lines, transverse 1- to 2-mm white bands, are due to arsenic, thallium, or lead poisoning. Longitudinal brown or black pigmented bands (melanonychia striataor longitudinal melanonychia) may indicate the presence of a melanocytic nevus or lentigo in the nail matrix (eFig. 366.15). Such bands are common in darkly pigmented races, but unusual in whites. Melanonychia occurs more frequently on the fingers than on toes, with the thumb most commonly affected. A solitary pigmented band that suddenly changes in color or becomes wider may warrant a nail matrix biopsy to exclude melanoma, even in an Asian or black individual.10 Extension of the pigment over the proximal nail fold (Hutchinson sign) is also suspicious for melanoma. Pigmented nail bands may also be seen in Addison disease, Laugier-Hunziker syndrome, HIV infection, and with medications such as chemotherapeutic agents and zidovudine. When associated with oral melanotic macules and intestinal polyps, Peutz-Jeghers syndrome is the likely diagnosis.

Blue discoloration of the lunulae may be seen in Wilson disease and with administration of zidovudine. Brown or black discoloration can be caused by drugs, such as doxorubicin, zidovudine, antimalarials, and minocycline. The yellow nail syndrome, rare in children, consists of thickened yellow nails, lymphedema, and respiratory disease. Yellow nails may also be seen with thyroid disease, nephrotic syndrome, immunoglobulin A deficiency, and mental retardation.