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75-Year-Old Male with Symmetric, Asymptomatic Rash on Arms

Can you diagnose this case?

Signs and Symptoms

This 75-year-old man presented with a symmetric, asymptomatic eruption on both arms that had failed various topical corticosteroid treatments.

What is the cause of this man’s arm rash?

Choose one to reveal diagnosis and discussion

Actinic keratosis
Lupus erythematosus
Photodrug reaction
Pityriasis lichenoides chronica
Lichen planus

Answer: Pityriasis lichenoides chronica

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A biopsy supported the diagnosis of pityriasis lichenoides chronica (PLC), a rare and poorly understood condition that manifests as a benign eruption with lymphocytic infiltrates of the skin. It presents as a persistent, erythematous, papular eruption with scale that is asymptomatic.

PLC is thought by some investigators to represent a hypersensitivity reaction to an infectious agent, since there have been reports of clustering of cases and familial outbreaks, and associated infection with Epstein-Barr virus.

Currently, there is no standard of treatment for PLC or its acute form, pityriasis lichenoides et varioliformis acuta. Broadband and narrowband UV-B phototherapy, psoralen combined with UV-A photochemotherapy, and methotrexate offer the most consistent therapeutic responses. Tetracycline has been shown to be effective in some patients, and slow tapering once resolution has been achieved has been shown to prevent recurrence.1

The other listed choices (actinic keratosis, lupus erythematosus, photodrug reaction, and lichen planus) are reasonable in the differential diagnosis, and a biopsy often is required to distinguish these conditions from PLC.

David L. Kaplan, MD, is a clinical assistant professor of dermatology at the University of Missouri–Kansas City School of Medicine in Kansas City, Missouri, and at the University of Kansas School of Medicine in Kansas City, Kansas. He practices adult and pediatric dermatology in Overland Park, Kansas.

Reference:

1. Henning JS. Pityriasis lichenoides chronica. Dermatol Online J. 2004;10(3):8.

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