Pityriasis rosea

Pityriasis rosea is a common, often pruritic rash. The initial eruption manifests as a single ovoid macule (herald patch) and is followed by a secondary eruption of multiple scaly papules distributed in a classic Christmas tree pattern on the trunk. Patients may experience a flu-like prodrome. Pityriasis rosea is thought to be triggered by a viral infection and most commonly affects young adults, especially female individuals. Diagnosis is clinical. Lesions usually resolve without intervention within 6–12 weeks; management of pruritus may include emollients, topical steroid creams, and/or oral antihistamines. For persistent, severe, or widespread disease, treatment with acyclovir may be considered. Specialist consultation is indicated for pregnant individuals with rash onset before 15 weeks' gestation, who have an increased risk of negative pregnancy outcomes (e.g., preterm birth, stillbirth, spontaneous abortion).

• 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 HHV 7) is suspected based on the following: ^[2]
  • 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 affected individuals): herald patch (mother patch) ; ^[1]
  • Single ovoid macule or patch, 1–5 cm in diameter
  • Slightly raised, dark red border with a central salmon-colored clearing zone ^[4][5]
  • Lesion surrounded by a collarette: a ring-like, fine, white scale (like cigarette paper) ^[6]
  • Typically on the trunk
• Secondary eruption (2–21 days later) ; ^[1][2]
  • Bilateral diffuse, oval-shaped papules and plaques (< 1.5 cm) with scaly collarette
    • Salmon-colored in individuals with light skin
    • May be hyperpigmented in individuals with dark skin
  • Papules appear along Langer lines, which align on the back like the branches of a Christmas tree (Christmas tree appearance)
  • Rash typically occurs on the trunk, neck, and upper extremities; scalp and face are more likely to be affected in individuals with dark skin than in individuals with light skin.
• Pruritus occurs in 80–90% of affected individuals. ^[3]
• Postinflammatory hypopigmentation or hyperpigmentation, especially for individuals with dark skin

Atypical pityriasis rosea manifests with variation in rash appearance (e.g., vesicular), distribution (e.g., face, scalp, groin, axilla), size of lesions (e.g., small papular lesions, giant lesions), and/or number of lesions. ^[2]

• Diagnosis is clinical.
• Consider the following for diagnostic uncertainty, atypical manifestation, and/or persistent (> 3 months) rash:
  • Diagnostics for dermatophyte infections (e.g., KOH test) to exclude tinea
  • Diagnostics for syphilis to exclude secondary syphilis
  • Skin biopsy ^[3]

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

The differential diagnoses listed here are not exhaustive.

• Advise patients that spontaneous resolution typically occurs within 6–12 weeks. ^[1][4]
• Consider symptomatic treatment for pruritus as necessary, although evidence to support these treatments, all of which are off-label, is limited. ^[3][7]
  • Topical emollient (e.g., calamine lotion)
  • Topical corticosteroid
  • Acyclovir ^[2][7]
    • Consider in pityriasis rosea in pregnancy or persistent (> 3 months), severe, or relapsing rash.
    • Avoid in children and breastfeeding patients.
  • Oral antihistamine
  • Oral macrolide, e.g., erythromycin
  • UVB phototherapy (severe disease)

Relapse, while rare, typically occurs within 5–18 months. ^[1]

Pityriasis rosea in pregnancy ^[2][7][8]

• More common in pregnant individuals than in the general population
• Pityriasis rosea prior can 15 weeks' gestation can: ^[8]
  • Manifest with more severe symptoms (e.g., widespread lesions and systemic symptoms)
  • Lead to complications (e.g., preterm birth, stillbirth, spontaneous abortion)
• Diagnostics for pityriasis rosea are the same as in nonpregnant individuals.
• Consider specialist referral (e.g., maternal-fetal medicine), especially if onset before 15 weeks' gestation and/or oral lesions, for: ^[8]
  • Additional monitoring (e.g., fetal ultrasound)
  • Consideration of acyclovir (off-label) ^[1][7]