Psoriasis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Syed Hassan A. Kazmi BSc, MD [2]

Classification

Psoriasis can be classified according to clinical appearence, morphology and localization.

• The International Psoriasis Council, identifies four main forms of psoriasis:
  • Plaque-type psoriasis
  • Guttate psoriasis
  • Generalized Pustular Psoriasis (GPP)
  • Erythroderma

Several further subphenotypes have been named according to distribution (localized vs. widespread), anatomical localization (flexural- also called inverse, scalp, palms/soles/nail), size (large vs. small) and thickness (thick vs. thin) of plaques, onset (early vs. late), and disease activity (active vs. stable).

Plaque-type Psoriasis

• Plaque-type psoriasis is the most common form of psoriasis affecting patients.
• It is characterized by oval or irregularly shaped, red, sharply demarcated, raised plaques covered by silvery scales.
• Plaques occur usually on the extensor surface of elbows and knees, on the scalp, and on the lower back, but can affect almost any area of the body.
• Large plaques are >3cm in size and small scales are <3cm is size.

Guttate Psoriasis

• Guttate psoriasis is characterized by multiple, small, drop-shaped, scaly plaques usually occurring around the trunk and upper extremities and thighs.
• It is sudden onset, usually occurs within 2–4 wk after a bacterial infection of the upper ways, notably streptococcal pharyngitis in children and adolescents.
• Lesions can either resolve spontaneously or progress to plaque-type psoriasis.

Generalized pustular psoriasis

• Generalized pustular psoriasis is a relatively rare form of psoriasis but can be potentially life-threatening.
• It is characterized by episodic, widespread skin and systemic inflammation.
• Typical histological hallmark of GPP is the presence of prominent aggregates of neutrophils infiltrating the stratum spinosum (spongiform pustules of Kogoj) and giving rise to sterile cutaneous pustules.
• There may be high fever, fatigue and leukocytosis.
• Triggers include:
  • Pregnancy
  • Infection
  • Exposure to or withdrawal from drugs

Erythrodermic Psoriasis

• Erythromdermic psoriasis is the rarest form of psoriasis but is the severest form.
• It is characterized by diffuse erythema which includes greater than seventy percent of the human body.
• Systemic manifestations such as hypothermia and extremity edema might be present because of the generalized vasodilation underlying the erythema, as well as myalgiafatigue and fever.

Other types of psoriasis

• Flexural psoriasis (inverse psoriasis) appears as smooth inflamed patches of skin. It occurs in skin folds, particularly around the genitals (between the thigh and groin), axillae, under an overweight stomach (pannus), and under the breasts (inframammary fold). It is aggravated by friction and sweat, and is vulnerable to fungal infections.
• Nail psoriasis produces a variety of changes in the appearance of finger and toe nails. These changes include discolouring under the nail plate, pitting of the nails, lines going across the nails, thickening of the skin under the nail, and the loosening (onycholysis) and crumbling of the nail.
• Drug-induced psoriasis
• Napkin psoriasis
• Seborrheic-like psoriasis
• Pustular psoriasis

• 

  Photograph of an arm covered with plaque psoriasis.

• 

  Psoriasis nail pitting

Severity

Pie chart showing the distribution of severity among people with psoriasis.

Psoriasis is usually graded as:

• Mild (affecting less than 3% of the body)
• Moderate (affecting 3-10% of the body)
• Severe

Several scales exist for measuring the severity of psoriasis. The degree of severity is generally based on the following factors:

• The proportion of body surface area affected
• Disease activity (degree of plaque redness, thickness and scaling)
• Response to previous therapies
• The impact of the disease on the person.

Psoriasis Area Severity Index (PASI)

The Psoriasis Area Severity Index (PASI) is the most widely used measurement tool for psoriasis. PASI combines the assessment of the severity of lesions and the area affected into a single score in the range 0 (no disease) to 72 (maximal disease). The PASI can be too unwieldy to use outside of trials, which has led to attempts to simplify the index for clinical use.