Henoch-Schönlein Purpura (HSP): This condition is the most likely diagnosis due to the presence of non-blanching palpable purpura, which is a hallmark of HSP. It typically affects children and young adults, presenting with purpura on the legs, arms, and buttocks, and can be accompanied by abdominal pain, arthritis, and renal involvement.

Vasculitis (e.g., microscopic polyangiitis, granulomatosis with polyangiitis): These conditions can present with similar skin manifestations, including palpable purpura, and often involve other organs such as the kidneys and lungs.
Infection-related vasculitis: Certain infections, like meningococcemia or Rocky Mountain spotted fever, can cause a vasculitic rash that resembles palpable purpura.
Thrombocytopenia or platelet dysfunction: Conditions that lead to low platelet counts or impaired platelet function can cause purpura, although these are typically not palpable.

Meningococcemia: This is a life-threatening infection that can cause a rash resembling palpable purpura. Early recognition and treatment are crucial to prevent severe complications and death.
Disseminated intravascular coagulation (DIC): DIC can cause widespread thrombosis and bleeding, including purpura, and is often associated with severe underlying conditions such as sepsis or trauma.
Thrombotic thrombocytopenic purpura (TTP): TTP is a rare disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, and renal failure, which can present with purpura.

Ehlers-Danlos syndrome: This genetic disorder can cause easy bruising and purpura due to fragile blood vessels and skin.
Pseudoxanthoma elasticum: A rare genetic disorder that affects the elastic fibers in the skin, leading to easy bruising and purpura.
Amyloidosis: A condition characterized by the deposition of amyloid proteins in various tissues, including the skin, which can cause purpura.