A 28-year-old man is in the office for a work physical and asks about the white streaks on his fingernail (Figure 198-1). He has had them on and off all of his adult life, but recently developed more of them and was concerned that he might have a vitamin deficiency. He was 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. (Reproduced with permission from Richard P. Usatine, MD.)
The anatomy of the nail unit is shown in Figure 198-2. 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 and 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. (Reproduced with permission from Usatine R, Pfenninger J, Stulberg D, et al. Dermatologic and Cosmetic Procedures in Office Practice. Philadelphia, PA: Elsevier, Inc; 2012.)
Melanonychia often involves several nails and is a more common occurrence in patients with darker skin types. Among African Americans, benign melanonychia affects up to 77% of young adults and nearly 100% of those age 50 years or older. In the Japanese, LM affects 10% to 20% of adults.1 The incidences of most other benign nail findings are not well established.
ETIOLOGY AND PATHOPHYSIOLOGY
Leukonychia refers to benign, single or multiple white spots or lines in the nails. Patchy patterns of partial, transverse white streaks (transverse striate leukonychia, see Figure 198-1) or spots (leukonychia punctata, Figure 198-3) are the most common patterns of leukonychia.2 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 in industrialized countries.
Most commonly, no specific cause for leukonychia can be found. ...