Continuing Medical Education
Psoriasis of the nail: Anatomy, pathology, clinical presentation, and a review of the literature on therapy

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Psoriasis is a chronic skin disease that affects millions of people throughout the world. Even though cutaneous signs and symptoms are the most common clinical manifestations, the nails can be involved in up to 50% of cases, and their involvement remains an important yet often overlooked aspect of the disease. There is a broad spectrum of nail dystrophies associated with psoriasis, ranging from the common pitting and loosening of the nail plate to the less frequent discoloration and splinter hemorrhages seen in the nail bed. This article discusses the normal anatomy and embryology of the nail unit as well as the current understanding of the pathogenesis of the disease. It also provides an extensive review of the existing literature with respect to psoriatic nail therapy. Although there have been many recent advances in the treatment of the cutaneous form of the disease—most notably in the field of immunotherapies—the options for nail psoriasis are far more limited. While a number of treatment alternatives currently exist for nail disease, the general paucity of clear evidence regarding these choices often makes it difficult to select the most efficient, safe, and optimal treatment for the patient. Even though the current literature has shown some support for the use of topical, intralesional, radiation, systemic, and combination therapies for nail psoriasis, the available studies lack sufficient power to extrapolate a standardized therapeutic regimen. Therefore, until better-documented evidence validating the treatment options emerges within the literature, clinicians and patients are left with a vague and relatively unproven approach to psoriatic nail disease.

Section snippets

The nail

Over the years, a number of sources have extensively described the anatomic, embryologic, and clinical aspects of nail disease. Baran and Dawber,10 Scher and Daniel,11 and Samman and Fenton9 have provided excellent resources that were used throughout this article. However, the majority of the information regarding the various aspects of the nail unit was attained from the publications of Zaias,12, 13, 14, 15 whose work on nails is among the most comprehensive within the current literature.

Embryology

The earliest signs of cellular growth and differentiation related to nail development are seen as early as 8 weeks' gestation. The first anatomically recognizable feature, however, is visible at 9 weeks' gestation.12 At this early age, an invagination of the primitive epidermis forms an uninterrupted groove that delineates a flattened surface at the end of each digit, known as the nail field (Fig 3).

At 11 weeks, the proximal nail field displays the beginnings of a structure known as the matrix

Immunology of psoriasis

Historically, psoriasis was considered to be an abnormal proliferation and differentiation of keratinocytes. However, the discovery that patients with psoriasis who underwent organ transplantation and subsequently received cyclosporine A to prevent graft rejection showed improvement in their skin disease was the first indication that psoriasis was a disease of immunology as opposed to abnormal keratinization.19 Ensuing studies using cyclosporine20 and denileukin difitox21, 22 to treat

Treatment

Although there have been many recent advances in the treatment of skin psoriasis, the options for nail psoriasis are far more limited in scope and efficacy. The general paucity of well-documented clinical studies makes it difficult to select an ideal therapy, because the current modalities are often tedious to administer with short-lived remissions. Nail psoriasis tends to be persistent and refractory to treatment, and so it is understandable that a standardized therapeutic regimen does not

Conclusions and future trends

As nail psoriasis is one of the lesser-studied disorders within the field of dermatology, its treatment still remains relatively ambiguous. With a lifetime incidence of 80% to 90% amongst psoriatics,9 it remains an often overlooked yet important aspect of psoriasis treatment. Although the therapeutic options for skin psoriasis are considerably broader and far more proven than those for nail disease, several treatment alternatives still exist. However, the scarcity of well-documented evidence

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    Funding source: None.

    Conflicts of interest: None declared.

    Presented at the 13th Annual European Academy of Dermatology & Venereology Annual Meeting, November 12-13, 2004, Manchester, UK.

    Reprints not available from the authors.

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