Series Editor: Herbert L. Fred, MD

Prepared by Mary Elizabeth Rushing, MD, Resident, and Daniel Sheehan, MD, Assistant Professor, Section of Dermatology, Medical College of Georgia, Augusta

A 72-year-old black man presented with a 2-month history of an itchy rash that appeared after he had started taking allopurinol for gout. He had numerous purple, scaly papules on his antecubital fossae, extending dorsally over the extensor aspect of both forearms (Figure). A lacy, white, reticulated pattern was noted over a few papules. Punch biopsy of one of the lesions showed a lymphocytic lichenoid infiltrate with eosinophils in the dermis.

Points to remember: The 4 Ps—purple, polygonal, pruritic, papules—describe lichen planus or a lichen planus–like eruption. A lichenoid drug eruption (LDE) is distinct from lichen planus in several ways. A LDE typically occurs in older patients, has a photodistribution, and has subtle differences from lichen planus on histologic analysis (eg, parakeratosis).

Many drugs have been implicated in LDE, with different frequencies. Angiotensin-converting-enzyme inhibitors, thiazide diuretics, and beta-blockers play a more prominent role than do nonsteroidal antiinflammatory drugs, lorazepam, simvastatin, and allopurinol. Typically, a LDE has a latent period of several months from start of the drug to the cutaneous eruption, as opposed to the hours-to-weeks onset from other drugs. The diagnosis is supported by resolution of the eruption after withdrawing the drug. LDE differs from lichen planus histologically by the presence of eosinophils or plasma cells.

Diagnosis: Lichenoid drug eruption.