• Clinical science

Parapsoriasis

Abstract

The term “parapsoriasis” covers a large group of idiopathic cutaneous diseases characterized by asymptomatic or mildly pruritic, erythematous, scaly patches, and a chronic course. The condition is roughly classified into two types: large plaque parapsoriasis and small plaque parapsoriasis. Large plaque parapsoriasis is considered a premalignant condition that can progress to mycosis fungoides. Diagnosis is based on clinical examination and histopathological findings on biopsy. Treatment includes topical steroid therapy and phototherapy.

Epidemiology

  • Rare disorder
  • Sex: >

Epidemiological data refers to the US, unless otherwise specified.

Etiology

  • Group of cutaneous diseases of unknown etiology
  • Skin lesions (i.e., papules, patches, or plaques) caused by T-cell infiltration into the skin

The term “parapsoriasis” has its roots in its dermatological similarity to psoriatic lesions (e.g., plaques and scaly patches) seen during efflorescence.

Small plaque parapsoriasis

  • Clinical features
    • Round or oval, scaly, salmon-colored or yellow-brown patches
      • Size: < 5 cm diameter
      • Location: trunk, flanks, proximal extremities in non-sun exposed areas
      • Digitate dermatosis: a distinct type that looks like finger-like impressions over the trunk; dermatomal pattern
    • Benign; chronic course (months to years); resolves spontaneously
  • Diagnostics: Skin biopsy
  • Treatment
    • Asymptomatic: topical emollients or no treatment required
    • Symptomatic

Large plaque parapsoriasis

  • Clinical features
    • Irregularly-shaped, scaly, atrophic , salmon-colored, brown, or erythematous patches
      • Size: ≥ 5 cm diameter
      • Location: trunk, buttocks, thighs, flexor surfaces, and breasts (areas not exposed to sun)
    • Considered a premalignant condition; may progress to mycosis fungoides
  • Diagnostics: skin biopsy
  • Treatment: always indicated, because treament may prevent progression to mycosis fungoides or cutaneous T-cell lymphoma.

Differential diagnoses

Differential diagnosis of Parapsoriasis
Small plaque psoriasis
  • Round or oval, scaly, salmon-colored or yellow-brown patches < 5 cm diameter
  • Location: non-sun exposed areas
  • Resolve spontaneously
Large plaque psoriasis
Mycosis fungoides
Pityriasis rosea
  • Flu-like symptoms followed by a Herald patch
  • Location: back
  • Resolves within weeks
Nummular eczema
  • 2–5 cm, coin-shaped, well-demarcated erythematous plaques with scabs
  • Location: all extremities
  • Chronic condition
Psoriasis
  • Well- demarcated, erythematous pruritic plaques with silvery scaling
  • Location: scalp, extensor surfaces, back; nail involvement
  • Chronic with symptom-free intervals

The differential diagnoses listed here are not exhaustive.