An 80-year-old-woman was seen as an inpatient hospital consult. A persistent pruritic eruption had developed acutely on the legs. She was on a ward reserved primarily for cardiac patients.
Key point: The discrete locations and almost square shape suggest an external cause. In this case, the patient was allergic to the propylene glycol found in the conducting gel applied underneath ECG electrodes.
Treatment: Twice-daily application of a potent topical corticosteroid will alleviate this transient but uncomfortable rash.
Note: Another possibility to consider might be an allergy to nickel if the ECG electrodes have any metal on them, or to the acrylic adhesive found on the popular disposable ECG electrodes.