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A 19-year-old man with a 4-year history of plaque psoriasis presents with nail abnormalities in several fingers (Figure 195-1). He is particularly concerned about the recently acquired greenish discoloration of his fifth digit.

Figure 195-1

Patient with nail psoriasis demonstrating the oil drop sign (second digit), nail pitting (second and third digit), onycholysis (second, fourth and fifth digit), and secondary pseudomonas infection (fifth digit). (Courtesy of E.J. Mayeaux, Jr., MD.)

Psoriasis is a hereditary disorder of skin with numerous clinical expressions. It affects millions of people throughout the world.1 Nail involvement is common and can have a significant cosmetic impact.

  • Nails are involved in 30% to 50% of psoriasis patients at any given time, and up to 90% develop nail changes over their lifetime.1 In most cases, nail involvement coexists with cutaneous psoriasis, although the skin surrounding the affected nails need not be involved. Psoriatic nail disease without overt cutaneous disease occurs in 1% to 5% of psoriasis. Patients with nail involvement are thought to have a higher incidence of associated arthritis.2
  • The most common nail change seen with psoriasis is nail plate pitting (Figures 195-1 and 195-2).

Figure 195-2

Nail psoriasis demonstrating nail pitting, onycholysis, oil drop sign, and longitudinal ridging. Nails held over the silvery plaque on the knee. (Courtesy of Richard P. Usatine, MD.)

  • In psoriasis, parakeratotic cells within the stratum corneum of the nail matrix alters normal keratinization.3 The proximal nail matrix forms the superficial portion of the nail plate, so that involvement in this part of the matrix results in pitting of the nail plate (Figures 195-1 and 195-2.) The pits may range in size from pinpoint depressions to large punched-out lesions. People without psoriasis can have nail pitting.
  • Longitudinal matrix involvement produces longitudinal nail ridging or splitting (Figure 195-2). When transverse matrix involvement occurs, solitary or multiple “growth arrest” lines (Beau lines) may occur (see Chapter 190, Normal Nail Variants). Psoriatic involvement of the intermediate portion of the nail matrix leads to leukonychia and diminished nail plate integrity.
  • Parakeratosis of the nail bed with thickening of the stratum corneum causes discoloration of the nail bed, producing the “salmon spot” or “oil drop” signs.3
  • Desquamation of parakeratotic cells at the hyponychium leads to onycholysis, which may allow for bacteria and fungi infection.4

  • Psoriasis of the skin.
  • Psoriatic arthritis.
  • Nail unit trauma.
  • Generalized psoriasis flair.

Clinical Features

  • The diagnosis of nail psoriasis is usually straightforward when characteristic nail findings coexist with cutaneous psoriasis. Nail pitting and onycholysis are the most common findings (Figure 195-3).
  • Nail psoriasis and onychomycosis are often indistinguishable by clinical examination alone. Psoriasis ...

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