Psoriasis

Original article by Asad Mahmood | Last updated on 2/6/2014
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Pathology

Keratinocyte hyperproliferation: differentiation, or ‘skin cell going from basal layer to horny layer’, reduced from 4 weeks to 4 days [approximately!]
Histopathological features:
  • Parakeratosis: retained nuclei
  • Acanthosis: thick epidermis
  • Absent granular layer
  • Lengthened rete ridges
  • Thin dermal papillae
  • Dilated, tortuous capillaries
  • Munro’s micro-abscesses
  • T-cells in upper dermis
 

Clinical features

Age: 15-40 years; esp. in 30s
Types
  • Classical [or typical]
    • Plaques: Well-circumscribed erythematous plaques with silver scaling
    • Distribution: Esp. on extensor surfaces [elbow, knee], scalp/hairline, sacral
    • Features: Pain, itch [but less than eczema/dermatitis]
    • Auspitzs sign: Bleeding on scale removal
  • Guttate
    • Age: Young
    • Onset: Follows streptococcal tonsillitis
    • Plaques: Multiple discoid erythematous and scaly macules and plaques on trunk
  • Palmoplanar pustular
    • Plaques: Yellow-brown pustules on palms and soles
  • Flexoral
    • Plaques: Erythematous, but not scaly
    • Distribution: Submammary, axillary, anogenital, umbilical
    • Epidemiology: Esp. women; also the elderly and HIV +ve
  • Erythrodermic [emergency!]
    • Features: Acute onset of erythroderma and pustular plaques
    • Management: Methotrexate
    • Others: only scales; only nails; and napkin

Nails

  • Features: Pitting, onycholysis [nail lifting off the bed]; subungal hyperkeratosis; Beaus lines [horizontal, across the nail]
  • Differential diagnosis: fungal infection, alopecia areata

Psoriatic arthropathy

  • Patterns: [1] AnkSpond-like/spondylitis; [2] RA-like/symmetrical; [3] Asymmetrical, <3 joints;[4] DIP joints, hands; [5] Arthritis multilans
 

Differential diagnosis

  • Dermatitis/eczema: discoid or seborrhoeic
  • Lichen planus
  • Pityriasis rosea [esp. guttate psoriasis]
  • 2o stage of syphilis
  • Reiter’s syndrome [Esp. palmoplanar psoriasis]
  • Discoid lupus
 

Precipitating factors

  • Trauma [known as Koebner’s phenomena]
  • Drugs: β-blockers, lithium, anti-malarials; NSAIDs and ACE-Is
  • Stress
  • Sunlight
  • ‘Genetic’
 

Management

Topical
  • Emollients
  • Vit. D analogues
    • Calcipotriol, tacalcitol and calcitriol
    • Mechanism: ↓ cell proliferation
    • Side-effects: Skin irritation, hypercalaemia if overdose
  • Coal tar preparations
    • Mechanism: Inhibit DNA synthesis
    • Problems: Smelly, messy
  • Dithranol
    • Anthralin
    • Mechanism: ↓ cell proliferation
    • Side-effects: Irritates neighbouring normal skin, stains clothes purple
  • Keratolytics
    • Salicylic acid
  • Corticosteroids
    • Caution: Not alone, as may cause brittle psoriasis on rebound
  • Retinoids
    • Tazarotene

Systemic

  • Immunosuppressants
    • Methotrexate
    • Also ciclosporin, azathioprine, and hydroxyurea
  • Retinoids
    • Acitretin
    • Note: Therapeutic effect after 4-6 weeks; used for <6 months
    • Side-effects
      • Teratogenic for up to 3 years
      • Dry mucous membranes: skin, eyes, lips [may cause epistaxis]
      • Others: hepatotoxicity; deranged lipid profile
  • Photo[chemo]therapy
    • UVB for classic/plaque and guttate types
    • PUVA [psoralen] for palmoplanar type
  • Treating classic/typical psoriasis
    • 1st line: Dithranol
    • 2nd line: Vit. D analogues or topical steroids + tar or salicylic acid ± UVB
    • 3rd line: Retinoids, PUVA + immunosuppressants
    • Goekerman regime = Tar + UVB
    • Ingram regime = Goekerman + dithranol