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 the International Psoriasis Council, psoriasis may be classified into four subtypes: plaque-type psoriasis, guttate psoriasis, generalized pustular psoriasis (GPP), and 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

Classification based on clinical appearance, morphology, and localization

• The International Psoriasis Council classifies psoriasis into four main forms, according to clinical appearance, morphology and localization:
  • Plaque-type psoriasis
  • Guttate psoriasis
  • Generalized Pustular Psoriasis (GPP)
  • Erythroderma

Type of Psoriasis	Typical lesion	Body Distribution	Associated conditions
Plaque-type psoriasis	Oval or irregularly shaped Erythematous Sharply demarcated Raised plaques covered by silvery scales	Large plaques >3cm Small plaques <3cm Extensor surface of elbows and knees Scalp Lower back	Psoriatic arthritis Metabolic syndrome Inflammatory bowel disease Non-melanoma skin cancer Triggers include: Drugs including: Lithium Antimalarials Withdrawal of systemic steroids Beta blockers Non-steroidal anti-inflammatory drugs(NSAIDS) Angiotensin-converting enzyme (ACE) inhibitors Trazodone Terfenadine Gemfibrozil Antibiotics (tetracycline, penicillin) Imiquimod
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: 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	Generalized	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

Classification based on subphenotypes

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)
• Thickness (thick vs. thin) of plaques
• Onset (early vs. late)
• Disease activity (active vs. stable)

Classification based on severity

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 ranging between 0 (no disease) to 72 (maximal disease). The PASI can be very difficult to use outside of trials, which has led to attempts to simplify the index for clinical use.

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 discoloring under the nail plate, pitting of the nails, lines going across the nails, thickening of the skin under the nail, and the loosening (onycholysis) or crumbling of the nail.
• Drug-induced psoriasis
• Napkin psoriasis
• Seborrheic-like psoriasis
• Pustular psoriasis