Which skin rash is pathognomonic of rheumatic fever?

Erythema marginatum is a distinctive skin rash that is pathognomonic for rheumatic fever. This type of rash typically presents as pink or red macules and papules that have a serpiginous or "wavy" appearance, often with a pale center. It usually appears on the trunk and proximal limbs and is associated with the underlying inflammation of rheumatic fever, which is a complication of streptococcal throat infection. Recognizing this rash is important as it helps confirm the diagnosis of rheumatic fever along with other clinical criteria.

Other rashes, like erythema nodosum, diffuse petechiae, and purulent bullae, are not specific to rheumatic fever. Erythema nodosum is characterized by painful nodules on the lower legs and can be associated with a variety of conditions, including infections and autoimmune diseases. Diffuse petechiae are small red or purple spots caused by bleeding under the skin and can occur in various conditions unrelated to rheumatic fever. Purulent bullae are associated with bacterial infections and represent localized collections of pus, which do not correlate with the pathophysiology of rheumatic fever. Understanding the specificity of erythema marginatum in the context of rhe