Parapsoriasis

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.

• Rare disorder
• Sex: ♂ > ♀

References:^[1][2][3]

Epidemiological data refers to the US, unless otherwise specified.

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

References:^[2]

• 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
  • Benign; chronic course (months to years); resolves spontaneously
• Diagnostics: Skin biopsy
• Treatment
  • Asymptomatic: topical emollients or no treatment required
  • Symptomatic
    • Mid- to high-potency steroid therapy
    • Phototherapy for refractory or wide-spread skin lesions
      • PUVA therapy
      • SUP (selective ultraviolet phototherapy)

References:^[1][2][3][4]

• 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 treatment may prevent progression to mycosis fungoides
  • High-potency topical steroids
  • Phototherapy for refractory or widespread plaques
    • PUVA therapy
    • SUP (selective ultraviolet phototherapy)
  • Monitor for progression to mycosis fungoides

References:^[2]

• See Differential diagnosis of scaling
• Further differentials:
  • Mycosis fungoides
  • Pityriasis rosea
  • Tinea versicolor

References:^[2]

The differential diagnoses listed here are not exhaustive.