A 19-year-old man with a 4-year history of plaque psoriasis presents with nail abnormalities in several fingers (Figure 203-1). He is particularly concerned about the recently acquired greenish discoloration of his fifth digit.
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). (Reproduced with permission from 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 66% of psoriasis patients at any given time, and 80% to 90% develop nail changes over their lifetime.1,2 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 cases.
Patients with nail involvement are thought to have a higher incidence of associated arthritis.2,3 Among patients with psoriatic arthritis, the prevalence of nail psoriasis is greater than 80%.4 Psoriatic nail disease may be considered an indicator for patients at risk for future psoriatic joint damage.5
The most common nail change seen with psoriasis is nail plate pitting (Figures 203-1 and 203-2).
ETIOLOGY AND PATHOPHYSIOLOGY
In psoriasis, parakeratotic cells within the stratum corneum of the nail matrix alter normal keratinization.4 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 (see Figures 203-1 and 203-2). 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 (see Figure 203-2). When transverse matrix involvement occurs, solitary or multiple "growth arrest" lines (Beau lines) may occur (see Chapter 198, 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 patch" or "oil drop" signs.6
Desquamation of parakeratotic cells at the hyponychium leads to onycholysis, which may allow for bacterial and fungal infection.7
Nail psoriasis demonstrating nail pitting, onycholysis, oil-drop sign, and longitudinal ridging. Nails held over the silvery plaque on the knee. (Reproduced with permission from Richard P. Usatine, MD.)