Pityriasis Rosea

Pityriasis rosea is a common, self-limited papulosquamous eruption of young adults, thought to relate to reactivation of human herpesvirus 6 and 7.

• Incidence is 0.5 to 2% per year, peak at 10 to 35 years, slightly more in women, in spring and autumn.
• Duration is 4 to 10 weeks (up to 5 months). Recurrences are rare (about 2%).
• Drug induced pityriasis rosea like eruptions occur with captopril, ACE inhibitors, bupropion, imatinib, isotretinoin, and TNF inhibitors.
• Early pregnancy disease (under 15 weeks) is associated with miscarriage, preterm delivery and neonatal hypotonia in a minority.

• Herald patch: a solitary 2 to 10 cm oval, salmon pink plaque with a collarette of scale, in 50 to 90%, usually on the trunk.
• 1 to 2 weeks later, oval pink macules and papules with fine collarette scale along Langer lines, producing a "Christmas tree" pattern on the back.
• Mild itch (25 to 50%), mild prodromal malaise; mucous membranes spared.
• Variants: inverse (flexural), papular, urticarial, vesicular, and purpuric.

• Clinical diagnosis.
• Syphilis serology (RPR/VDRL, treponemal test) in all sexually active patients; HIV test if risk factors.
• KOH microscopy and fungal culture if tinea corporis is suspected.
• Biopsy if atypical: focal parakeratosis, spongiosis, extravasated red cells.
• Exclude secondary syphilis, guttate psoriasis, nummular eczema, tinea corporis, lichen planus, pityriasis lichenoides chronica, and drug eruptions.

• Reassure about benign natural history, which clears spontaneously in 6 to 8 weeks.
• Itch: emollients, calamine lotion, menthol 0.5% in aqueous cream, mild topical steroids (hydrocortisone 1% or betamethasone valerate 0.1% twice daily), and non-sedating antihistamines (cetirizine 10 mg).
• Avoid hot baths and irritants.
• Antiviral therapy: aciclovir 800 mg five times daily for 7 days, given within the first week of onset, reduces duration and severity (modest benefit).
• Extensive or persistent disease: narrow band UVB 3 times weekly for 2 to 3 weeks, or a short prednisolone course (0.5 mg/kg for 7 days) in severe cases (use cautiously).
• Pregnancy: refer for obstetric review in first 15 weeks; aciclovir may be considered.
• Pigmentary change resolves over months.