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Patient Story
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A 3-year-old girl presents with one year of rashes from head to toe that are not responding to topical steroids. The girl’s mother and her chart reflect a diagnosis of severe atopic dermatitis. The physician meticulously examines the girl’s skin and nails and finds splinter hemorrhages, pitting, longitudinal ridging and onycholysis in the fingernails with splinter hemorrhages and nail thickening of the toenails (Figure 165-1). With this new information in mind, the physician notes other skin findings that are more suggestive of psoriasis than atopic dermatitis. This careful examination of the nails leads the clinician to the correct diagnosis and more effective treatment of the psoriasis.

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FIGURE 165-1

Nail psoriasis in a 3-year-old girl that helped to correctly diagnose her skin rash as psoriasis and not atopic dermatitis. A. Note the nail pitting, onycholysis, oil drop sign, longitudinal ridging and splinter hemorrhages in the fingernails. B. Note the splinter hemorrhages and nail thickening in the toenails. (Used with permission from Richard P. Usatine, MD.)

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Introduction
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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.

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Epidemiology
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  • Nails are involved in 30 to 50 percent of psoriasis patients at any given time, and up to 90 percent 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 percent 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 165-1 and 165-2).

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Etiology and Pathophysiology
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  • 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 165-1 and 165-2.) 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 165-3). When transverse matrix involvement occurs, solitary or multiple “growth arrest” lines (Beau lines) may occur (see Chapter 160, 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 (Figure 165-4).3

  • Desquamation of parakeratotic ...

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