What is the characteristic feature of Henoch-Schönlein purpura?

Henoch-Schönlein purpura (HSP), also known as IgA vasculitis, is characterized by the presence of palpable purpura, typically located on the lower extremities and buttocks. This skin manifestation occurs due to small vessel vasculitis leading to inflammation and subsequent leakage of blood into the skin, resulting in the purplish spots. HSP predominantly affects children and is associated with a preceding upper respiratory infection in many cases.

Understanding the distinctive feature of palpable purpura helps clinicians diagnose HSP and differentiate it from other conditions that may present similarly, but with different underlying mechanisms and types of lesions. While other symptoms may accompany HSP, such as abdominal pain or arthralgia, the hallmark finding of palpable purpura on the lower extremities is critical for establishing the diagnosis.