• Clinical science

Pityriasis rosea

Abstract

Pityriasis rosea is a self-limiting rash commonly affecting young adults, especially females. The etiology is mostly unknown, although it is thought to be caused by a viral infection. The majority of patients present with a solitary, coin-sized "herald patch,” followed by multiple, oval, scaly papules distributed in a classic "Christmas tree” pattern on the trunk. Except for mild pruritus, pityriasis rosea is asymptomatic. The lesions disappear within two months, often causing postinflammatory hyperpigmentation or hypopigmentation. Typically, only symptomatic treatment of pruritus with lotions, oral antihistamines, and/or a short course of topical steroids is necessary.

Epidemiology

  • Age range: 10–35 years of age
  • Sex: > (reason unknown)

References:[1]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

  • Idiopathic
  • A viral etiology is suspected based on the following:
    • Pityriasis rosea can occur in clusters, affecting many people living in the same community.
    • Seasonal variations (more common in the spring and fall)
    • Preceded by a prodromal flu-like illness in some patients
    • Ampicillin can worsen the rash distribution
    • Immunological evidence (lack of B-cell activity)
    • Life-long immunity (recurrence is rare but possible)

References:[1]

Clinical features

  • Prodrome: (1–2 weeks prior to rash onset): flu-like symptoms (e.g., malaise, fever, pharyngitis)
  • Initial eruption (∼ 90% of cases): herald patch (mother patch)
    • Single ovoid macule or patch, 2–10 cm in diameter
    • Slightly raised, dark red border with a central salmon-colored clearing zone
    • Surrounded by a collarette: a collar of fine , white scales (like cigarette paper)
    • Typically on the back
  • Secondary eruption (2–21 days later)
    • Bilateral diffuse, oval-shaped, salmon-colored papules and plaques (< 1.5 cm) with scaly collarette
    • Papules appear along Langer's lines; , which align on the back like the branches of a Christmas tree (Christmas tree appearance)
    • Typically seen on the trunk (thorax, back, abdomen), neck, and upper extremities
  • In children: The classic distribution of the rash is not seen. The lesions involve the scalp, face, hand and feet, while sparing the trunk (an inverse distribution). In some children, the rash primarily affects the groin and axillary regions.
  • Pruritus may occur in 25–75% of cases.
  • Postinflammatory hypopigmentation or hyperpigmentation (resolves over several months)

References:[1]

Diagnostics

  • Usually a clinical diagnosis
  • Laboratory tests may be considered if the diagnosis is uncertain.
  • If the rash does not resolve after 3–4 months, the presentation is atypical, or the diagnosis is uncertain → biopsy

References:[1]

Treatment

  • Spontaneous resolution within 6–8 weeks
  • Mild cases
    • Avoid irritants (harsh soaps or fragrances, sweating, scratching)
    • Antipruritic therapy
      • Topical emollients, zinc oxide lotion/calamine lotion (or menthol-phenol, pramoxine, or oatmeal)
      • Oral antihistamines
  • Severe cases (severe pruritus or widespread rash)

References:[2][3]