Pityriasis Rosea

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

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 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]

Treatment

Complications

• Post-inflammatory hyperpigmentation, especially in skin of color (months to fade)
• Pruritus disrupting sleep
• Possible adverse pregnancy outcomes (preterm delivery, fetal loss) if early gestation — limited evidence
• Diagnostic delay missing secondary syphilis

PANCE pearls

• ALWAYS check RPR/VDRL in sexually active adults with PR — secondary syphilis is the great mimicker (the 'great imitator').
• Herald patch may be misdiagnosed as tinea — KOH is helpful when in doubt; collarette scale faces inward in PR vs outward border in tinea.
• Christmas-tree pattern is best seen on the back with lesions oriented along Langer lines.
• Atypical PR (inverse, predominantly facial, palmoplantar involvement, vesicular, hemorrhagic) should prompt biopsy and broader workup.
• PR is self-limited — patients want a name and a timeline, not an aggressive treatment.

References

• AAFP 2018 — Pityriasis Rosea: Diagnosis and Treatment (Eisman, Sinclair, Am Fam Physician 2018)
• Drago HHV — Pityriasis Rosea and Human Herpesvirus 6 and 7 (Drago et al., J Am Acad Dermatol 2014)
• Pregnancy PR — Pityriasis Rosea in Pregnancy: Outcomes and Recommendations (Drago et al., J Am Acad Dermatol 2008)