About 50% of nail deformities are caused by a fungal infection (see Nail Disorders: Onychomycosis). The remainder result from various causes, including trauma, psoriasis, lichen planus, and occasionally cancer. Drugs, infections, and diseases can cause discoloration of the nails (chromonychia). For example, infection with Pseudomonas bacteria can cause a yellow-green discoloration (see Nail Disorders: Green Nail Syndrome).
The doctor can often make a diagnosis by examination. However, to confirm the diagnosis, the doctor may need to take fungal scrapings and perform a culture (the process of growing the organisms in a laboratory). If the nail's appearance does not improve with treatment of the underlying disorder, manicurists may be able to hide deformities with appropriate trimming and polishes.
Some babies are born without nails (anonychia). In nail-patella syndrome (see Hereditary Connective Tissue Disorders: Nail-Patella Syndrome), nails are missing or are small with pitting and ridges. Darier's disease causes red and white streaks on the nails and V-shaped notches to form on the tips of the nails.
Deformities Associated With Disease:
Sometimes, diseases that involve other organs can cause changes in the nails as well.
Deformities Associated With Skin Diseases:
Sometimes, skin diseases also affect the nail unit and may change the appearance of the nails. Some drugs given to treat skin diseases can change the nail plate. For example, retinoids, such as isotretinoin and etretinate, can cause dryness and brittleness of the nails.
Different drugs lead to discoloration of the nail, which usually gets better after the drug is stopped and the nail grows out.
Melanonychia striata are brown-black lines in the nail plate caused by the brown pigment melanin. The lines extend from the base of the nail to its tip. In dark-skinned people, these lines may be normal and require no treatment. Similar pigment changes can also be caused by moles or skin cancer around or under the nail, so doctors need to evaluate the surrounding skin.
Onychogryphosis is a disorder in which the nail, most often on the big toe, becomes thickened and takes on an extremely curved, hooked appearance (ram's horn nail). The curved hooked nail may injure an adjoining toe and is caused by one side of the nail growing faster than the other. This disorder involves damage to the nail bed, which is most often caused by repetitive injury (such as by ill-fitting shoes), but may also occur in disorders such as psoriasis. Onychogryphosis is common in older people. The nails should be kept trimmed, and injury to nearby toes can be prevented by placing lamb's wool between the toes. Footwear or stockings that gather at the toes should be avoided.
Onycholysis is separation of the nail plate from the nail bed or complete nail plate loss. It can occur from trauma (as in prolonged hiking or skiing with ill-fitting footgear); from overzealous nail cleaning; with diseases such as psoriasis and thyrotoxicosis; or from exposure to certain chemicals or drugs. Drugs that cause onycholysis include doxorubicin, bleomycin, captopril, 5-fluorouricil, and retinoids. Other drugs, including tetracyclines, psoralens, fluoroquinolones, and quinine, may cause onycholysis most often when the nails are exposed to sunlight (photo-onycholysis).
People with onycholysis are at risk of infection with yeast and fungus. Keeping the nail dry and applying antifungal preparations to the nail unit can help. Partial onycholysis may occur in people with a fungal infection.
People with this disorder pick at and tear their nails. The most common manifestation is the habit-tic deformity, in which the person frequently picks at or rubs the central cuticle with a neighboring finger. This is most often seen on the thumb and leads to a washboard-like appearance in the center of the nail plate. Onychotillomania can also cause bleeding beneath the nails (subungual hemorrhage), infection in the nail unit, and even complete loss of the nail plate.
Last full review/revision August 2007 by Wingfield E. Rehmus, MD, MPH