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]

Overview

Psoriasis can be classified according to clinical appearance, morphology and localization. According to International Psoriasis Council, psoriasis may be classified into 4 subtypes: 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).

Classification

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

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

Type of Psoriasis	Typical lesion	Body Distribution	Associated conditions
Plaque-type psoriasis (most common)	Oval or irregularly shaped, red, sharply demarcated, raised plaques covered by silvery scales.	Large plaques > 3cm Small plaques < 3cm Extensor surface of elbows and knees Scalp Lower back
Guttate psoriasis	Multiple, small, drop-shaped, scaly plaques	trunk Upper extremities Thighs	2–4 weeks after a bacterial infection of the upper ways, notably streptococcal pharyngitis in children and adolescents
Generalized pustular psoriasis	Four sub-types namely: Zumbusch (erythema, sheeted pustulation and scarlatiniform peeling) Annular (gyrate and annular pustular lesions) Localized (restricted areas of pustular psoriasis in and around ordinary psoriatic plaques) Exanthematic (single short-lived episode following infection or drug exposure) Episodic, widespread skin and systemic inflammation. Sheeted, pinhead-sized, sterile, sub-corneal pustules		High fever fatigue leukocytosis Triggers include: Pregnancy Infection Exposure to or withdrawal from drugs
Erythrodermic psoriasis (most severe)	Diffuse erythema	>70 % of the body surface area	Hypothermia Extremity edema Myalgias Fatigue High grade fever

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).

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

Degree of severity

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.