Approach

PR manifests as an acute, self-limited, inflammatory eruption characterized by a single larger lesion, the herald patch, followed by eruption of smaller papulosquamous oval lesions. Diagnosis is usually based on clinical history and findings, although in some patients, skin biopsy and/or additional serology may be necessary to confirm the diagnosis.

Clinical features

Lesions present mostly on the trunk and upper extremities.[12] Less commonly, the face, palms, and soles of the feet may be affected, although this can be seen more often in children.[3][4][12] The characteristic "herald patch," found in up to 80% of cases, is the largest lesion and the first to arise, usually on the trunk.[4][8] It begins as a single papule and expands into a pink erythematous oval patch or plaque up to 10 cm in diameter. Typically it has a raised border with free edge inside (collarette) and a central scale.[3][7][12] Occasionally multiple herald patches may be seen.[17] This is followed by an eruption of smaller papulosquamous oval lesions after 7 to 10 days, although a delay of up to 84 days has been reported.[4] The long axes of these oval lesions are aligned along lines of skin cleavage ("Langer lines") on the trunk, creating a fir-tree pattern of branches with the spine as the trunk, a V distribution over the chest and upper back, circumferentially over the shoulders and hips, and a horizontal distribution over the lower trunk.[3][7] Pruritus is a feature in 75% of patients and is moderate to severe in 50% of patients.[7][12] Infrequently, there can be oral lesions including petechiae, erosions, ulcers, vesicles, papules, and strawberry tongue, with petechiae and erosions/ulcerations being most common.[18]

In a small proportion of cases (5%), prodromal symptoms may be reported, including fever, malaise, headache, and arthralgia.[2][3][7] As recurrences can occur, a previous history of PR may be reported.[12][Figure caption and citation for the preceding image starts]: Herald patch in classic distribution on the upper torsoFrom the collection of Daniela Kroshinsky, MD, MPH; used with permission [Citation ends].com.bmj.content.model.Caption@4ff50e1f

Skin biopsy and histopathology

Skin biopsy can be used to confirm atypical or confusing cases and to exclude other diagnoses. Histopathologic evaluation will demonstrate a superficial perivascular lymphohistiocytic infiltrate with focal spongiosis, focal parakeratosis in mounds, dyskeratotic keratinocytes, papillary dermal edema, possible dermal eosinophils, and extravasated red blood cells.[7]

Additional laboratory investigations

If infectious etiology is suspected, for example fever, malaise, and sore throat, antistreptolysin O titers may be measured to exclude streptococcal infection and/or guttate psoriasis. If only a few lesions are present, potassium hydroxide (KOH) prep microscopy or fungal culture may be performed to exclude fungal infection, such as Tinea. Consider serology for Treponema pallidum in selected patients. This includes patients at risk for secondary syphilis, and cases with atypical lesions or with palmoplantar involvement.[19][20]

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