Pityriasis rosea (PR) is a self-limited papulosquamous eruption characterized by a herald patch followed by a secondary exanthem of oval, erythematous plaques with collarette scale along cleavage lines, producing a “Christmas-tree” pattern on the trunk. Human herpesviruses 6 and 7 reactivation is implicated. PR typically resolves within 6–10 weeks; management focuses on pruritus control and patient reassurance. Atypical variants and pregnancy-associated cases may warrant additional evaluation and treatment.
Epidemiology
- Common in adolescents and young adults; slight seasonal peaks.
- Incidence estimated at 0.3–2% lifetime risk.
- Recurrence is uncommon but possible.
Pathophysiology
- Likely linked to systemic reactivation of HHV-6/7 with T cell–mediated skin response.
- Vaccine- or drug-related PR-like eruptions reported (e.g., ACE inhibitors, NSAIDs, terbinafine, biologics); these are “PR-like” and may last longer.
Clinical Features
- Herald patch: solitary oval plaque, 2–5 cm, with peripheral collarette scale; often on trunk or proximal limb; precedes the exanthem by 1–2 weeks.
- Secondary eruption: multiple smaller oval lesions following Langer’s lines on trunk and proximal extremities (“Christmas-tree” on back).
- Pruritus variable; prodromal symptoms (malaise, headache) in a minority.
- Variants: inverse (axillae/groin), acral, vesicular, papular (children, darker skin types), giant plaques, mucosal lesions (rare).
Differential Diagnosis
- Tinea corporis (KOH to exclude), guttate psoriasis, secondary syphilis (palms/soles, systemic symptoms—screen with serology if sexually active or atypical), pityriasis lichenoides, nummular eczema, drug eruption.
Diagnosis
- Clinical pattern recognition; dermoscopy can show peripheral collarette scaling.
- KOH if tinea suspected; RPR/VDRL if syphilis risk or atypical distribution; biopsy rarely needed (shows focal parakeratosis with spongiosis and extravasated RBCs).
Management
- Reassurance: self-limited, average duration 6–10 weeks.
- Pruritus relief: topical corticosteroids (low-to-mid potency), oral antihistamines, emollients; menthol/calamine.
- Phototherapy: NB-UVB early in course can reduce itch and hasten resolution in severe cases.
- Antivirals: small RCTs suggest high-dose acyclovir (e.g., 800 mg five times daily for 7 days, or 400–800 mg five times daily depending on study) may shorten duration in severe/early PR; consider in significant symptomatic cases after risk-benefit review.
- Avoid triggers: heat, friction; gentle skin care.
Special Considerations
- Pregnancy: PR in early pregnancy has been associated (controversially) with adverse outcomes; test for syphilis; consider acyclovir in severe early cases and obstetric coordination; close follow-up.
- Drug-induced PR-like eruptions: review medication list; discontinuation may be needed.
Prognosis
- Excellent; postinflammatory dyspigmentation may linger, especially in skin of color; scarring is not typical.
References (recent guidelines and key reviews)
- Evidence reviews on PR diagnosis and management, 2021–2024.
- Studies on HHV-6/7 reactivation in PR, 2022–2024.
- Randomized trials/meta-analyses of acyclovir and phototherapy in PR, 2021–2024.