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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Figure 1

Lower back showing a spectrum of lesion ages. A new inflammatory lesion (A). Older lesion demonstrating fading (B).

Skin reactions to transdermal rivastigmine patches (transdermal therapeutic systems) are relatively common, occurring in 11.4%–24.5% of patients1 but the severity of the reaction is usually mild to moderate.1 2 However, unlike a rectangular plaster or dressing, the circular shape of the patch means that the resulting patch of dermatitis can be confused with an endogenous inflammatory rash such as tinea corporis, erythema multiforme or granuloma annulare. The key to the diagnosis usually lies in the history and examination—a spectrum of lesions of varying ages is suggestive, and the use of a patch can be confirmed by the patient or their carers.