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 British Columbia, Department of Dermatology and Skin Science.
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