An Annular Plaque on the Back
Am Fam Physician. 2017 Aug 15;96(4):255-256.
A 24-year-old man presented with a three-week history of a mildly pruritic, spreading rash. Before the generalized skin eruption, there was a single plaque on his back. Fatigue and upper respiratory symptoms preceded the appearance of the rash. There was no history of trauma to the area, including friction or rubbing. He had not recently used any topical agents or new medications.
Physical examination revealed multiple erythematous, scaly patches of varying size on the trunk and extremities (Figures 1 and 2). The plaques had a central wrinkled, salmon-colored area and a dark-red peripheral zone.
Based on the patient's history and physical examination findings, which one of the following is the most likely diagnosis?
A. Granuloma annulare.
B. Guttate psoriasis.
C. Pityriasis rosea.
D. Tinea corporis.
The answer is C: pityriasis rosea. Typically, pityriasis rosea begins with a single erythematous, scaly patch on the trunk (herald patch). The herald patch appears one to 20 days before the generalized rash of pityriasis rosea. It is an oval, salmon-colored or red plaque with a scale trailing just inside the edge of the lesion like a collarette. The herald patch is usually 1.5 to 5 cm in size.
The generalized rash includes numerous smaller (1 cm), scaly, pink patches that develop on the trunk along the lines of skin cleavage. This has often been described as a Christmas tree pattern because skin cleavage lines run diagonally on the back. Pityriasis rosea lasts an average of eight to 12 weeks, although longer and shorter courses have been reported. The cause of pityriasis rosea is unknown, but there is some evidence of an infectious etiology. Pityriasis rosea resolves without treatment in one to three months.1,2
Granuloma annulare is a noninfectious gra
REFERENCESshow all references
1. Eisman S, Sinclair R. Pityriasis rosea. BMJ. 2015;351: h5233....
2. Browning JC. An update on pityriasis rosea and other similar childhood exanthems. Curr Opin Pediatr. 2009; 21(4):481–485.
3. Hsu S, Le EH, Khoshevis MR. Differential diagnosis of annular lesions. Am Fam Physician. 2001;64(2): 289–267.
4. Keimig EL. Granuloma annulare. Dermatol Clin. 2015; 33(3):315–329.
5. Raychaudhuri SK, Maverakis E, Raychaudhuri SP. Diagnosis and classification of psoriasis. Autoimmun Rev. 2014;13(4–5):490–495.
This series is coordinated by John E. Delzell Jr., MD, MSPH, Assistant Medical Editor.
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