Pityriasis rosea

Pityriasis rosea is a self-limiting rash that most commonly affects young adults, especially females. Although the exact etiology is unknown, pityriasis rosea is thought to be triggered by 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 typically 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.

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

Epidemiological data refers to the US, unless otherwise specified.

• Idiopathic
• A viral etiology (HHV 6 and 7) is suspected based on the following: ^[1]
  • 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
  • Life-long immunity (recurrence is rare but possible)

• 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 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
• Pruritus may occur in 25–75% of cases.
• Postinflammatory hypopigmentation or hyperpigmentation (resolves over several months)

• Usually a clinical diagnosis
• Laboratory tests may be considered if the diagnosis is uncertain.
  • KOH preparation: to exclude tinea
  • RPR or VDRL: to exclude secondary syphilis
• Biopsy: if the rash does not resolve after 3–4 months, the presentation is atypical, or the diagnosis is uncertain

• Tinea corporis
• Pityriasis versicolor
• Drug eruptions
• Psoriasis
• Lichen planus
• Secondary syphilis
• For details, see “Overview of annular skin lesions.”

The differential diagnoses listed here are not exhaustive.

• 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)
  • Topical steroid creams (short course)
  • UVB phototherapy in resistant cases
  • Acyclovir or macrolide antibiotics (e.g., erythromycin) may be useful.

• Spontaneous abortion: pityriasis rosea during pregnancy is associated with increased risk of spontaneous abortions.

We list the most important complications. The selection is not exhaustive.