A 14-year-old boy was brought into the office for a well-child visit and his mother pointed out white streaks in his fingernail (Figure 160-1). He has had them for about a year and his mother is concerned that he may have a vitamin deficiency. They were reassured that this is a normal nail finding often associated with minor trauma.
Transverse striate leukonychia (transverse white streaks) in a healthy patient. Note that the lines do not extend all of the way to the lateral folds, which indicates a probable benign process. (Used with permission from Richard P. Usatine, MD.)
The anatomy of the nail unit is shown in Figure 160-2. The nail unit includes the nail matrix, nail plate, nail bed, cuticle, proximal and lateral folds, and fibrocollagenous supportive tissues. The proximal matrix produces the superficial aspects of the plate, and the distal matrix the deeper portions. The nail plate is composed of hard and soft keratins, is formed via onychokeratinization, which is similar to hair sheath keratinization.1 Most normal nail variants occur as a result of accentuation or disruption of normal nail formation.
The anatomy of the nail unit. (Used with permission from Usatine R, Pfenninger J, Stulberg D, Small R. Dermatologic and Cosmetic Procedures in Office Practice. Elsevier, Inc., Philadelphia. 2012.)
Melanonychia often involves several nails and is a more common occurrence in those patients with darker skin types. Among African Americans, benign melanonychia affects up to 77 percent of young adults and nearly 100 percent of those age 50 years or older. In the Japanese, LM affects 10 to 20 percent of adults.1 Nail matrix nevi have been reported to represent approximately 12 percent of LM in adults and 48 percent in children.2 The incidences of most other benign nail findings are not well established.
Etiology and Pathophysiology
Leukonychia represents benign, single or multiple, white spots or lines in the nails. Patchy patterns of partial, transverse white streaks (transverse striate leukonychia, Figure 160-1) or spots (leukonychia punctata, Figure 160-3) are the most common patterns of leukonychia.3 Leukonychia is common in children and becomes less frequent with age. Parents may fear that it represents a dietary deficiency, in particular a lack of calcium, but this concern is almost always unfounded.
Most commonly, no specific cause for leukonychia can be found. It is usually the result of ...