Psoriasis affects men and women equally and typically runs a chronic course that is marked by frequent relapses. It occurs worldwide and affects approximately 1% of the population in the United States. Psoriasis can have its onset at any age, but is most likely to appear in early adulthood. Although its exact etiology is unknown, it is clear that psoriatic skin is in a hyperproliferative state with a marked increase
in the rate of keratinocyte replication.
SIGNS
Psoriasis is a classic example of a papulosquamous disease, characterized by erythematous papules and plaques with a silvery scale. The disorder
can vary from a focal disease consisting of localized lesions to a widespread eruption and even a generalized erythroderma with exfoliation. The characteristic early lesion of psoriasis is an erythematous papule with a scale that can be subtle but is usually obvious. Typically, the papules gradually expand and coalesce to form sharply demarcated,
symmetrically distributed plaques.
Frequently, the plaques become surrounded by a thin zone of perilesional blanching, known as a Woronoff ring. This ring is most frequently seen in the early stages of resolution in ultraviolet (UV) light therapy. Although some authorities
have shown evidence of prostaglandin inhibition to explain this phenomenon, the precise
mechanisms involved are likely to be more complex. Psoriasis can occur at any cutaneous site, although it has a predilection for the scalp, elbows,
knees, extensor aspects of the extremities, and the nails. It also frequently involves the penis . Oral lesions are unusual in psoriasis; however, some authorities believe that the condition known as geographic tongue may actually be a manifestation of psoriasis, because the histological features are identical. Occasionally, only intertriginous areas are involved (inverse psoriasis).
The scale in psoriasis is typically silvery white and stacked in layers. In this way, the scale is said to be micaceous (slatelike). When the scale is removed with curettage or scraping, pinpoint bleeding may be noted. This is known as the Auspitz sign. It is more common, however, to observe a loose scale that easily flakes off in patients with
long-standing lesions. Onycholysis—separation of the distal free edge of the nail plate from the nail bed—is a frequent finding. Less common, but more specific, is nail pitting—actual punctate depressions on the surface of the plate. The most specific nail finding, often said to be pathognomonic, is the so-called "oil spot," which describes a yellowish
brown, irregular macule beneath the nail plate and represents involvement of the nail bed with sis. When the nail matrix is involved, severe onychodystrophy can result, with diffuse crumbling and yellowing of the plate. In pustular psoriasis and acrodermatitis continua of Hallopeau, one commonly observes subungual pustules.
Types of Psoriasis
Psoriasis Vulgaris
Psoriasis Vulgaris is the most frequent presentation
of psoriasis, consisting of chronic, stable, welldefined plaques that may persist for years. While the plaques can occur on any cutaneous surface, they are most likely to appear in the areas of predilection described above.
Guttate Psoriasis - Guttate psoriasis most commonly occurs in young
adults and is usually eruptive in onset. It consists of multiple, small, guttate (raindroplike) lesions over the trunk and proximal extremities (Figure 20-7).
Frequently, careful history-taking will reveal an antecedent streptococcal pharyngitis or viral respiratory infection.
Localized Pustular Psoriasis - Localized pustular psoriasis consists of two types: pustular psoriasis of the palms and soles, known as pustulosis palmoplantaris, and acrodermatitis continua of Hallopeau. Both forms present with pustules, the former involving the palms and soles, and the latter involving the distal fingers and toes with severe nail dystrophy. Both conditions are noted for chronicity and refractoriness to treatment. When severe, either can be disabling. Pustulosis palmoplantaris has been
associated with arthritis of the anterior chest wall, cigarette smoking, and thyroid disease.
Generalized Pustular Psoriasis - Generalized pustular (von Zambusch) psoriasis
is one of the rarer presentations of psoriasis, marked by acute attacks of generalized pustules on erythematous skin and associated with fever, leukocytosis, and systemic toxicity. This disease can be fatal, so hospitalization is mandatory. Several
provocative factors are claimed to precipitate attacks, but the most important to consider is the association with steroid withdrawal (ie, systemic
and potent topical steroids).
Psoriatic Arthritis - Psoriatic arthritis is an inflammatory, sero-negative
arthritis clearly associated with psoriasis.
TREATMENT
Numerous therapies are available for the treatment
of psoriasis. This fact speaks for the complexity of the disease, the mystery of its pathogenesis, and the limitations of all of the available treatments.
More information about Treatment of Psoriasis