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Nail Disorders

»	What functions do nails serve?
»	Why are nails important in medicine?
»	Do any systemic diseases have specific nail findings?
»	What are Beau’s lines? How are they formed?
»	What is a splinter hemorrhage?
»	Are splinter hemorrhages always associated with subacute bacterial endocarditis?
»	What is the difference between Mees’ lines and Muehrcke’s lines?
»	What are “half-and-half” nails, and with what internal disease are they associated?
»	What is nail fold capillaroscopy? How is it useful?
»	What is clubbing?
»	How is hypertrophic osteoarthropathy related to clubbing?
»	What is the yellow nail syndrome?
»	Are there any characteristic nail changes in primarily dermatologic diseases?
»	What are nail pits?
»	Are there any differences between the nail pits of psoriasis and alopecia areata?
»	What other nail findings are seen in psoriasis? What is the significance of nail changes?
»	How does a pterygium differ from pterygium inversus unguium?
»	What is the most common cause and sequela of a subungual hematoma? How is it treated?
»	Do malignant melanomas occur in the nails?
»	How do you tell the difference between a subungual hematoma and a malignant melanoma?
»	What nail changes are considered peculiar to human immunodeficiency virus (HIV) infection?
»	What is onychocryptosis? Why does it occur?
»	What is a paronychia?
»	Which infectious organisms cause paronychia?
»	How do you treat an acute paronychia?
»	What is the most common cause of green nails?
»	What is the difference between onychomycosis and tinea unguium? What organisms most commonly cause tinea unguium? Where does the infection typically start?
»	List the antifungal medications most often used in the treatment of toenail onychomycosis.
»	What should patients expect when undergoing treatment of onychomycosis?
»	What is “habit tic” disorder? How is it different from median nail dystrophy?
»	List the common benign “tumors” that occur in and around the nail unit.
»	What is an exostosis?
»	Name the four most common malignant tumors of the nail unit.

How does a pterygium differ from pterygium inversus unguium?

Fig. 68.5 Lack of distal separation in a patient with scleroderma and pterygium inversus unguium. (Courtesy of James E. Fitzpatrick, MD.)

A pterygium, which is Greek for “wing,” is classically associated with lichen planus. Lichen planus attacks the nail-forming unit, the matrix, and causes permanent scarring. Because the nail plate at that site is no longer made, the proximal nail fold attaches to the nail bed directly, and both grow out distally. This produces the “winglike” appearance.

Pterygium inversus unguium occurs when the nail plate distally does not separate from the underlying digital bed skin. The fingertip ulcerations and scarring also seen in scleroderma contribute to the inability of the nail to separate (Fig. 68-5).