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 or 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 sub-phenotypes

Several further sub-phenotypes have been named according to:

• Distribution (localized vs. widespread)
• Anatomical localization (flexural or 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 disease severity

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Psoriasis is usually graded as:

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

Degree of severity

The degree of severity is generally judged 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 patient's quality of life

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:
  • Smooth, inflamed patches of skin
  • 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)
  • Aggravated by friction and sweat and is vulnerable to fungal infections
• Nail psoriasis:
  • Changes in the appearance of finger and toe nails:
  • Discoloration 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

Classification of psoriatic arthritis

Psoriatic arthritis may be classified based on severity into the following types:

• Mild psoriatic arthritis
• Moderate psoriatic arthritis
• Severe psoriatic arthritis

Type of psoriatic arthritis	Response to therapy	Quality of life
Mild psoriatic arthritis	NSAIDs	Minimal
Moderate psoriatic arthritis	Requires disease modifying anti-rheumatic drugs (DMARD) or tumor necrosis factor blockers (TNF-blockers)	Daily life tasks affected including mental and physical tasks/ No response to NSAIDs
Severe psoriatic arthritis	Requires disease modifying anti-rheumatic drugs (DMARD) plus tumor necrosis factor blockers (TNF-blockers) or biologic agents	Unable to perform major daily tasks of living without pain or dysfunction; large impact on physical and mental functions

Psoriatic arthritis also, may be classified into different subtypes as below table:

Subtype	Disease pattern	Percentage of patients affected	Radiological features				Histopathological features
			X-ray	Ultrasonography	Computed tomography|CT scan	MRI
Classical psoriatic arthritis	Involvement of the distal interphalangeal joints Involvement of nails	~5 %	Bony proliferation Bone erosion "Pencil-in-cup" deformity (distal head of a bone becomes pointed-like a sharpened pencil, and the neighboring surface becomes rounded due to erosion)	Synovitis Tenosynovitis Peritendinitis Retrocalcaneal or pre-Achilles bursitis	Useful in assessing spine disease Joint erosions Synovitis	Synovitis (usually secondary to extrasynovial involvement - helps to differentiate PsA from rheumatoid arthritis) Gadolinium contrast use can more reliably differentiate PsA from rheumatoid arthritis by relative enhancement and rate of enhancement on MRI Enthesitis Osteitis	Neovascularization Inflammatory infiltration with predominantly mononuclear cells (T lymphocytes, B lymphocytes and plasma cells, and macrophages) Synovial lining hyperplasia  High expression of E-selectin Synovial expression of S100A12
Destructive psoriatic arthritis (arthritis mutilans)	Severe joint destruction Involvement of any of the interphalangeal, metacarpophalangeal, or metatarsophalangeal joints Dactylitis Enthesitis Involvement of axial skeleton Involvement of nails Digital tapering (opera glass hands) Joint ankylosis	< 5 %
Symmetric polyarthritis	Involvement of joints on both sides of the body simultaneously Most similar to rheumatoid arthritis	~15 %
Asymmetric psoriatic arthritis	Involvement of < 3 joints Does not occur in the same joints on both sides of the body	~70 %
Ankylosing spondylitis-like psoriatic arthritis	Stiffness of the spine or neck, but can also affect the hands and feet, in a similar fashion to symmetric arthritis	~ 5 %