A differential diagnosis for annular lesions: contact dermatitis to transdermal rivastigmine patches

Description

During an appointment for an unrelated condition at a dermatology clinic, a 75-year-old man was noted to have a number of annular lesions on his trunk. The patient mentioned that he had been prescribed transdermal rivastigmine patches (Alzest 4.6mg/24h) for memory impairment 4 months previously. These were applied and left on for 24 hours before being replaced. He noticed that each patch left a red, pruritic area.

The patient was otherwise well, his only medication being an antihypertensive. He did not have any drug allergies or sensitivity to plasters.

On examination, there were multiple annular lesions scattered over his trunk with a predilection for the flanks (figure 1). These demonstrated an evolution of clinical features; more recent lesions were erythematous, inflamed plaques (figure 1A) which progressed into brown, postinflammatory patches (figure 1B) which gradually faded. All the lesions were well demarcated, circular and approximately 40 mm in diameter.

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