Pityriasis Rosea

Sources: Fitzpatrick's Dermatology, Andrews' Diseases of the Skin, Goldman-Cecil Medicine, Tintinalli's Emergency Medicine

Definition

Pityriasis rosea (PR) is a common, self-limited papulosquamous eruption. The name literally means "pink scales" (Gibert, 1860). It typically lasts 5 to 8 weeks and resolves without long-term sequelae.

Epidemiology

Worldwide distribution; all races affected
Incidence: ~160 cases per 100,000 person-years (US data); 0.64 per 100 dermatologic patients globally
Peak age: 10 to 35 years (cases reported from 3 months to 83 years)
Slight female predominance (F:M ratio ~1.39:1)
Possible seasonal clustering (some studies show more cases in spring and autumn)
Relapse is uncommon: 1.8-3.7%

Etiology and Pathogenesis

PR is most likely a viral exanthem. The leading hypothesis involves HHV-6 and/or HHV-7 (human herpesviruses):

HHV-7 DNA has been found in lesional skin, peripheral blood mononuclear cells, and plasma of PR patients, but not controls
HHV-7 may trigger reactivation of latent HHV-6
Both viruses are virtually universal in adults (HHV-6 seropositivity 80-100%; HHV-7 >85%), making causality difficult to prove definitively
The eruption may represent either primary infection or reactivation leading to viremia
HHV-2 and hepatitis C virus have also been implicated in isolated cases

Note: Case clustering, possible seasonal variation, and the resemblance to other viral exanthems all support an infectious cause.

Clinical Features

The Herald Patch (Primary Lesion)

Pityriasis rosea herald patch - large erythematous oval patch accompanied by smaller erythematous patches

Present in 50-90% of patients
A single, 3-5 cm oval erythematous scaly plaque on the trunk (rarely an extremity)
Has a collarette of fine scale just inside the periphery (scale points inward)
Precedes the generalized eruption by ~1-2 weeks in adults, ~4 weeks in children
Commonly mistaken for tinea corporis because it appears as an isolated scaling plaque

Secondary Eruption

Follows the herald patch by 1-2 weeks
Smaller (0.5-1.5 cm) salmon-pink oval patches and plaques, mainly on the trunk and proximal extremities
Long axis of lesions oriented parallel to skin cleavage lines (Langer's lines)
On the back, this creates the classic "Christmas tree" or "fir tree" pattern
Collarette of scale with the open (free) edge pointing inward - the "hanging curtain sign"
Palms and soles are typically spared
Face is usually spared (exception: children with darker skin)

Systemic Symptoms

Mild pruritus (can be moderate-severe in some)
Mild prodromal flu-like symptoms may precede the eruption in some patients
These symptoms are transient

Atypical Variants

Variant	Description
Papular variant	More common in children with darker skin; also more facial/scalp involvement
Vesicular variant	Vesicular lesions; can mimic chickenpox
Erythema multiforme-like	Target-like lesions
Purpuric variant	Petechiae/ecchymoses along Langer lines - may rarely be a sign of underlying leukemia
Inverse/localized	Confined to neck, axillae, groin, thighs
Unilateral	Asymmetric distribution
Giant PR	Very large plaques

In darker-skinned patients, lesions often resolve leaving post-inflammatory hypopigmentation.

Histopathology

Epidermal changes: Mounded parakeratosis with "liftoff," mild acanthosis, spongiosis
Dermal changes: Superficial perivascular lymphocytic infiltrate, red blood cell extravasation (erythrocyte extravasation is a hallmark)
Inflammatory infiltrate: predominantly lymphocytes, with neutrophils, histiocytes; occasional eosinophils
Herald patch may show slightly deeper infiltrate and more acanthosis compared to secondary lesions
Biopsy is non-specific but can help exclude other diagnoses

Diagnosis

Diagnosis is clinical in the vast majority of cases. Key features:

Herald patch
Christmas tree distribution on trunk
Oval lesions along skin cleavage lines
Collarette of scale (free edge inward)
Self-limited, 4-8 week course

Differential Diagnosis

Condition	Key Distinguishing Features
Secondary syphilis (most important!)	Involves palms and soles, no herald patch, more widespread lymphadenopathy, condylomata lata; RPR positive
Tinea corporis	Scale at periphery (not collarette), KOH positive
Guttate psoriasis	Lesions don't follow cleavage lines; scale thick and silvery; no herald patch
Nummular dermatitis	More circular (not oval), tiny vesicles, no collarette
Pityriasis lichenoides chronica	More chronic, persistent crops, no herald patch, more confluent scale, extremity-predominant
Lichen planus	More pruritic, Wickham striae, distal extremity and mucous membrane involvement
Seborrheic dermatitis	Face and scalp involvement
Drug reaction	No herald patch, temporal relation to drug exposure

Clinical pearl: Always rule out secondary syphilis, especially when palms and soles are involved - order a serology (RPR or VDRL).

Drug-Induced PR-like Eruptions

Several medications can cause a pityriasis rosea-like eruption:

ACE inhibitors (captopril, lisinopril)
Imatinib mesylate
Interferons
Gold, bismuth, arsenicals
Clonidine, barbiturates
Ketotifen
Adalimumab, lithium, acyclovir, ergotamine

Special Situation: PR in Pregnancy

This deserves careful attention:

Associated with adverse pregnancy outcomes, particularly in the first trimester
In PR onset before 15 weeks gestation: ~62% resulted in miscarriage in one study
Can also be associated with premature delivery and neonatal hypotonia/hyporeactivity
Women who develop PR during pregnancy, especially in the first trimester, should be monitored closely

Treatment

PR is self-limited; most patients need only reassurance and symptomatic management.

Treatment	Role
Reassurance	Explain self-limited nature (6-8 weeks)
Topical corticosteroids (e.g., triamcinolone 0.1% cream)	Reduce pruritus
Oral antihistamines	Reduce pruritus
Emollients (petroleum jelly-based)	Skin barrier support
UVB phototherapy or natural sunlight	May speed resolution of lesions
Acyclovir (high-dose)	May hasten recovery and reduce symptoms in severe or widespread cases; most evidence is for 400-800 mg 5x/day for 1 week
Macrolides (e.g., erythromycin)	NOT indicated - earlier evidence was not confirmed

Acyclovir is considered when: widespread eruption, severe pruritus, significant systemic symptoms, or pregnancy (to potentially reduce adverse outcomes). It is most beneficial if started early in the course.

Prognosis and Complications

Complete resolution in 6-8 weeks in most patients (range 4-16 weeks)
No long-term complications in healthy individuals
Can cause anxiety and depression in ~30% of cases due to uncertainty about the diagnosis
Recurrence is uncommon (1.8-3.7%)
Post-inflammatory hyperpigmentation or hypopigmentation may persist, especially in darker skin tones

Summary Table

Feature	Details
Cause	Likely HHV-6/HHV-7 reactivation
Age	Peaks 10-35 years
First lesion	Herald patch (3-5 cm oval, collarette of scale)
Distribution	Trunk, proximal extremities; Christmas tree pattern
Duration	4-8 weeks (self-limited)
Key DDx	Secondary syphilis (always rule out!)
Treatment	Symptomatic; acyclovir for severe cases
Pregnancy	Watch closely - risk of miscarriage in 1st trimester

Fitzpatrick's Dermatology (Chap. 31), pp. 550-554
Andrews' Diseases of the Skin, p. 1915
Goldman-Cecil Medicine, p. 4280
Tintinalli's Emergency Medicine, p. 1679

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