What are the different types of psoriasis as classified in Rooks textbook of Dermatology?

Classification of Psoriasis According to Rook's Textbook of Dermatology

According to the American Academy of Dermatology guidelines, psoriasis is classified into several distinct clinical variants based on morphological characteristics, with plaque psoriasis being the most common form, affecting over 80% of patients. 1

Main Types of Psoriasis

1. Plaque Psoriasis (Psoriasis Vulgaris)

• Most common form (>80% of cases)
• Characterized by well-demarcated, erythematous plaques with silvery scale
• Common locations: scalp, elbows, knees, and presacral region
• May demonstrate Auspitz sign (pinpoint bleeding when scale is removed) 2

2. Inverse (Flexural) Psoriasis

• Occurs in skin folds and flexural surfaces
• Features erythematous plaques with minimal scaling due to moisture in these areas
• Common locations: axillary, genital, perineal, intergluteal, inframammary areas, and antecubital fossae 1

3. Erythrodermic Psoriasis

• Generalized erythema covering nearly the entire body surface area
• Variable degrees of scaling
• Can develop gradually from chronic plaque disease or acutely
• Associated with systemic symptoms: chills, hypothermia, dehydration, fever, malaise
• Considered a dermatologic emergency due to risk of complications 1

4. Pustular Psoriasis

• Characterized by visible collections of neutrophils in the stratum corneum
• Two main subtypes:
  • Generalized pustular psoriasis (von Zumbusch variant): widespread pustules on erythematous background, accompanied by fever and toxicity
  • Localized pustular psoriasis: primarily affects palms and soles 1

5. Guttate Psoriasis

• Characterized by dew-drop-like, 1-10mm salmon-pink papules with fine scale
• Primarily affects trunk and proximal extremities
• Common in individuals younger than 30 years
• Often triggered by streptococcal infection
• Occurs in less than 2% of psoriasis patients 1

6. Nail Psoriasis (Psoriatic Onychodystrophy)

• Can occur in all psoriasis subtypes
• Affects fingernails in ~50% of patients and toenails in ~35%
• Characteristic findings: pitting, onycholysis, subungual hyperkeratosis, oil-drop sign
• Present in up to 90% of patients with psoriatic arthritis 1

7. Psoriatic Arthritis

• Inflammatory arthropathy associated with psoriasis
• Belongs to the seronegative spondyloarthropathies group
• Often accompanied by nail changes 1

8. Sebopsoriasis

• Overlapping features of seborrheic dermatitis and psoriasis
• Lesions occur at sites typical for seborrheic dermatitis
• Characterized by greasy scales with occasional silvery scales in some areas 3

Clinical Pearls

• Psoriasis severity is not determined solely by body surface area; location significantly impacts classification of severity
• Even limited disease (<5% BSA) in special locations (face, genitals, hands, feet, nails) can be considered severe due to disproportionate physical and emotional impact 2
• Diagnosis is primarily clinical, based on pattern recognition and morphologic evaluation 4
• No established universal diagnostic criteria exist for cutaneous psoriasis 4
• Common pitfalls include undertreatment of seemingly "mild" disease and failure to address psychological impact 2

The classification of psoriasis is important for determining appropriate treatment strategies and monitoring disease progression, as different subtypes may respond differently to various therapeutic approaches.