Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the characteristic sign of Erythema ab igne?

1. Red patches due to UV exposure

2. Skin changes due to heat exposure

3. Lesions from insect bites

4. Rash from allergic reaction

The correct answer is: Skin changes due to heat exposure

Erythema ab igne is characterized by skin changes that occur specifically as a result of prolonged exposure to heat, rather than direct sun exposure or other environmental factors. The condition typically manifests as a reticular or mottled erythematous patch on the skin, often in areas that have been subjected to repeated warmth, such as near a fire or heating device. The heat exposure leads to changes in the blood vessels, causing a localized reaction that results in discoloration of the skin. In contrast, the other conditions mentioned have their own distinct triggers and characteristics. Red patches from UV exposure refer to sunburn or photodermatitis, which are caused by ultraviolet light rather than heat. Lesions from insect bites result from the saliva of the insect provoking an immune response, leading to localized swelling, redness, and itchiness. A rash from an allergic reaction is due to the body's immune response to an allergen, which generally presents differently compared to the localized heat-induced changes seen in erythema ab igne. Thus, the correct identification of erythema ab igne as a result of heat exposure reflects the unique aspects of skin damage attributable to thermal sources rather than other causes.