Dermatology · PANCE / PANRE

Pityriasis Rosea

Self-limited papulosquamous eruption with herald patch and Christmas-tree distribution; likely HHV-6/7 reactivation.

Also known as: pityriasis rosea, PR, herald patch

Overview

A benign, self-limited papulosquamous eruption that begins with a single 'herald patch' followed 1-2 weeks later by a generalized symmetric eruption of oval salmon-colored plaques on the trunk and proximal extremities in a Christmas-tree (fir-tree) pattern.

Epidemiology

Affects 0.5-2% of the population annually. Most common ages 10-35. Slight female predominance. Increased incidence in spring and fall in temperate climates.

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Risk factors

Recent viral infection or upper respiratory symptoms (prodrome in ~50%)
Vaccination (some COVID-19 and other vaccines reported as triggers)
Medications (PR-like eruption): captopril, gold, isotretinoin, omeprazole, terbinafine, imatinib, NSAIDs

Pathophysiology

Strong evidence supports reactivation of human herpesviruses HHV-6 and HHV-7 with viremia and skin localization. Mild prodrome, seasonality, and rare recurrence (<3%) suggest infectious etiology. T-cell mediated inflammation produces interface and spongiotic dermatitis.

Clinical presentation

Symptoms

Mild prodrome (50%): headache, malaise, low-grade fever, sore throat
Pruritus mild to moderate (25-75%), occasionally severe
Asymptomatic in many patients

Signs / physical exam

Herald patch: 2-10 cm single oval, salmon-pink plaque with collarette of scale at periphery; usually on trunk; precedes generalized eruption by 1-2 weeks (sometimes weeks)
Secondary eruption: numerous smaller (0.5-2 cm) oval pink plaques with peripheral collarette of fine scale
Distribution: trunk and proximal extremities; long axis of lesions parallels skin tension (Langer) lines → 'Christmas tree' or 'fir tree' pattern on back
Spares face, palms, soles (typical) — palmoplantar involvement should prompt syphilis workup
Inverse pityriasis rosea: variant predominantly in axillae and groin; more common in children and skin of color

Classic findings

Herald patch + Christmas-tree distribution on trunk + collarette of scale on peripheral lesions.

Differential diagnosis

Secondary syphilis — MUST rule out — palmoplantar copper macules, lymphadenopathy, condyloma lata, mucous patches; positive RPR/FTA. Check RPR in all sexually active adults with PR-like eruption
Guttate psoriasis — Smaller drop-shaped lesions, silvery scale, post-streptococcal
Tinea corporis (multiple lesions) — Annular plaques with raised border; KOH positive
Nummular eczema — Coin-shaped pruritic plaques, not in Christmas-tree pattern
Pityriasis lichenoides chronica — Chronic recurrent crops of papules with mica-like scale, longer course
Drug-induced PR-like eruption — More widespread, less typical distribution, longer course; recent new drug
Lichen planus — Pruritic violaceous polygonal papules with Wickham striae

Diagnostic workup

Diagnostic criteria

Clinical: herald patch + secondary eruption in characteristic distribution + collarette of scale; self-limited course 6-8 weeks.

Labs

Clinical diagnosis
RPR/VDRL to exclude secondary syphilis in all sexually active adults
KOH of herald patch if tinea suspected
Skin biopsy rarely needed: spongiosis, parakeratosis in mounds, mild perivascular lymphocytic infiltrate, extravasated erythrocytes

Imaging

Not indicated

Diagnostic algorithm

flowchart TD
  A[Single oval scaly plaque<br/>'Herald patch'] --> B[1-2 weeks later]
  B --> C[Generalized eruption<br/>Trunk + proximal extremities]
  C --> D[Oval lesions parallel<br/>Langer lines = 'Christmas tree']
  D --> E{Sexually active<br/>adult?}
  E -->|Yes| F[Check RPR/VDRL<br/>Rule out 2° syphilis]
  E -->|No| G[Clinical diagnosis]
  F --> G
  G --> H[Reassure + symptomatic care<br/>Emollients, low-mid steroid, antihistamine]
  H --> I[Self-resolves in 6-8 weeks]
  I --> J{Pregnant<br/><15 wks?}
  J -->|Yes| K[OB consult; consider acyclovir;<br/>monitor for preterm delivery]
  J -->|No| L[No further workup]

Pityriasis rosea diagnostic and management algorithm.

Treatment

First-line

Reassurance — disease is self-limited, resolving in 6-8 weeks (range 2 weeks to 3 months) without scarring
Symptomatic care for pruritus: emollients, low-mid potency topical corticosteroid (triamcinolone 0.1%), oral antihistamines (cetirizine, hydroxyzine for sleep)
Oatmeal baths, calamine lotion for itch
Sun exposure or narrowband UVB phototherapy may shorten course for severe pruritus

Severe / extensive / unresponsive

Oral acyclovir 800 mg 5x/day × 7 days — modest evidence for faster resolution and itch relief if started in first week
Short course oral prednisone (rarely needed) — controversial, may prolong course