Definition
A.Pityriasis rosea is an acute, self-limiting, benign skin eruption characterized by a preceding herald patch
that is followed by widespread papulosquamous lesions.
Incidence
A.Pityriasis rosea is relatively common, with more than 75% of cases in individuals from 10 to 35 years of age.
B.Incidence is slightly higher in women than in men.
C.Incidence is higher during the spring and autumn.
Pathogenesis
A.Disease is idiopathic; some evidence exists to support viral origin or autoimmune disorder.
Predisposing Factors
A.Recent acute infection.
Common Complaints
A.Rash: Salmon-, pink-, or tawny-colored lesions generally concentrated in lower abdominal area, but may develop on arms, legs, and rarely on the face.
B.Mild pruritus.
Other Signs and Symptoms
A.Earliest lesions may be papular but may progress to 1- to 2-cm oval plaques.
B.Long axes of oval lesions run parallel to each other, hence the term Christmas tree distribution.
C.Preceding herald patch (2–10 cm with central clearing) closely resembles ringworm; usually appears abruptly a few days to several weeks prior to the generalized eruptive phase.
Subjective Data
A.Elicit information about occurrence of initial, single, 2- to 10-cm round-to-oval lesion.
B.Question the patient as to known contacts with similar symptoms. Small epidemics have been identified in fraternity houses and military bases.
Physical Examination
A.Check temperature to rule out any infection.
B.Inspect:
1.Examine all body surfaces with patient unclothed.
2.Look for characteristic lesions and distribution.
3.Check the mucous surfaces, palms, and soles, which are usually spared by pityriasis rosea.
Diagnostic Tests
A.Generally, none required; however, potassium hydroxide (KOH) wet preparation may be useful to distinguish herald patch from tinea corporis.
B.If necessary to confirm diagnosis, deep shave or punch biopsy of developed lesions.
C.Order serology to rule out syphilis, if applicable.
D.If unable to identify herald patch, a serologic test for syphilis should be ordered because syphilis may be clinically indistinguishable from pityriasis rosea.
E.White blood count normal; no specific lab markers for pityriasis rosea.
Differential Diagnoses
A.Pityriasis rosea.
B.Nummular eczema.
C.Tinea corporis.
D.Tinea versicolor.
E.Viral exanthems.
F.Drug eruptions:
1.Captopril.
2.Bismuth.
3.Barbiturates.
4.Clonidine.
5.Metronidazole.
G.Secondary syphilis.
H.Lichen planus.
I.Psoriasis.
Plan
A.General interventions:
1.Direct sunlight to point of minimal erythema hastens disappearance of lesions and decreases itching. UVB light in five consecutive daily exposures can decrease pruritus and shorten rash, particularly if administered within the first week of eruption.
2.Not proven to be contagious and relatively harmless, so isolation is not required.
B. 
See Section III: Patient Teaching Guide Pityriasis Rosea.
1.Advise patients disease is self-limiting and clears spontaneously in 2 to 3 months.
C.Pharmaceutical therapy:
1.Generally, none is required, but for itching the following recommendations exist: Group V topical steroids and oral antihistamines as per usual dosing.
2.Prednisone 20 mg twice daily for 1 to 2 weeks in rare cases of intense itching.
Follow-Up
A.None is required unless secondary bacterial infection develops. Reoccurrence is unusual after disease resolution.
Consultation/Referral
A.Consult or refer the patient to a physician when disease persists beyond 3 months.
Individual Considerations
A.Pregnancy: Disease has not been shown to affect fetus.
B.Geriatrics: Disease rarely seen in geriatric patients. Strongly consider other differential diagnoses, particularly drug reactions.
C.Geriatric red flags:
1.Avoid first-generation anticholinergics because of risk of confusion, dry mouth, constipation, and other anti-cholinergic effects or toxicity.