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Plaque Psoriasis

Practice Essentials

Psoriasis, which manifests most often as plaque psoriasis, is a chronic, relapsing, inflammatory skin disorder with a strong genetic basis. Plaque psoriasis (see the image below) is rarely life threatening, but it often is intractable to treatment.

Plaque psoriasis. Courtesy of University of Britis

Plaque psoriasis. Courtesy of University of British Columbia, Department of Dermatology and Skin Science.

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See Psoriasis: Manifestations, Management Options, and Mimics, a Critical Images slideshow, to help recognize the major psoriasis subtypes and distinguish them from other skin lesions.

Signs and symptoms

Psoriatic plaques are characterized as follows:

Raised and easily palpable – Owing to the thickened epidermis, expanded dermal vascular compartment, as well as infiltrate of neutrophils and lymphocytes

Irregular to oval in shape

One to several centimeters in size

Well defined, with sharply demarcated boundaries

Very distinctive rich, full red color; lesions on the legs sometimes carry a blue or violaceous tint

Typically have a dry, thin, silvery-white or micaceous scale

Typically have a high degree of uniformity, with few morphologic differences between the 2 sides

Range in number from a few to many at any given time

Most often located on the scalp, trunk, and limbs, with a predilection for extensor surfaces, such as the elbows and knees

Symmetrically distributed over the body

May, in the case of smaller plaques, coalesce into larger lesions, especially on the legs and sacral regions

Other manifestations of plaque psoriasis include the following:

Pruritus – One of the main symptoms of plaque psoriasis

Nail psoriasis – Nails may exhibit pitting, onycholysis, subungual hyperkeratosis, or the oil-drop sign

Inverse psoriasis – A variant of psoriasis that spares the typical extensor surfaces and affects intertriginous areas (ie, axillae, inguinal folds, inframammary creases) with minimal scale

Psoriatic arthritis – Occurs in approximately 10-20% of all cases of plaque psoriasis

Manifestations of the psoriatic arthritis include the following:

Red, warm, tender, and inflamed joints

Joint deformity

Dactylitis

Sausage digits

Children

In children with plaque psoriasis, plaques are not as thick, and the lesions are less scaly. Psoriasis often appears in the diaper region in infancy and in flexural areas in children. The disease more commonly affects the face in children than it does in adults.

Diagnosis

Laboratory studies

The diagnosis of psoriasis is almost always made on the basis of clinical findings. Laboratory investigations are rarely indicated.

Skin biopsy

Skin biopsy can confirm the diagnosis of plaque psoriasis. This procedure, however, is usually reserved for the evaluation of atypical cases or for excluding other conditions in cases of diagnostic uncertainty.

Histology

Histologic epidermal findings include the following:

Mitotic activity of basal keratinocytes is increased almost 50-fold, with keratinocytes migrating from the basal to the cornified layers in only 3-5 days rather than the normal 28-30 days

The epidermis becomes thickened or acanthotic in appearance, and the rete ridges increase in size

Abnormal keratinocyte differentiation is noted throughout the psoriatic plaques, as manifested by the loss of the granular layer

Alternating collections of neutrophils are sandwiched between layers of parakeratotic stratum corneum, which is virtually pathognomonic for psoriasis

Histologic dermal findings include the following:

Signs of inflammation can be observed throughout the dermis

Marked hypervascularity and an increase in the size of the dermal papillae occur

An activated CD3+ lymphocytic infiltrate is noted around blood vessels

An aggregation of neutrophils in the dermis occurs that extends up into the epidermis

Management

Topical therapy

Topical agents used (often concurrently) to treat plaque psoriasis include the following:

Corticosteroids

Coal tar

Anthralin

Calcipotriene

Tazarotene

Phototherapy

The two main forms of phototherapy are as follows:

Ultraviolet B (UVB) irradiation – UVB therapy is usually combined with one or more topical treatments

Psoralen plus ultraviolet A irradiation (PUVA) – This treatment uses the photosensitizing drug methoxsalen (8-methoxypsoralen) in combination with UVA irradiation to treat patients with more extensive disease

Systemic therapy

Systemic treatment is initiated only after topical treatments and phototherapy have proved unsuccessful. Systemic therapy should also be considered for patients with very active psoriatic arthritis, as well as for patients whose disease is physically, psychologically, socially, or economically disabling.

Biologic therapy

Biologic therapies provide selective, systemic, immunologically directed interventions, including the following, at key steps in the pathogenesis of plaque psoriasis
:

Inhibition of the initial cytokine release and Langerhans cell migration

Targeting of activated T cells, prevention of further T-cell activation, and elimination of pathologic T cells

Blockage of interactions that lead to T-cell activation or migration into tissue

Alteration of the balance of T-cell types

Inhibition of proinflammatory cytokines, such as tumor necrosis factor (TNF),
interleukin (IL)–12, IL-17, and IL-23

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