Differential Diagnosis for a Child with Purpuric Lesions in Lower Extremities

Single Most Likely Diagnosis

• Henoch-Schönlein Purpura (HSP): This is the most common form of vasculitis in children, characterized by purpuric lesions primarily on the lower extremities, buttocks, and elbows, often accompanied by abdominal pain, arthritis, and sometimes renal involvement. The typical age range and the distribution of the purpura make HSP a leading consideration.

Other Likely Diagnoses

• Idiopathic Thrombocytopenic Purpura (ITP): Characterized by isolated thrombocytopenia with an otherwise normal complete blood count and peripheral blood smear, ITP can present with purpuric lesions due to low platelet counts. It's a common cause of purpura in children but typically lacks the other systemic symptoms seen in HSP.
• Infection-related Purpura: Certain infections, such as meningococcemia, can cause purpuric lesions. While less common than HSP or ITP, infections are a critical consideration due to their potential severity.
• Allergic Purpura: This can occur due to allergic reactions to medications or other allergens, leading to vasculitis and purpura.

Do Not Miss Diagnoses

• Meningococcemia: Although less common, this condition is life-threatening and can present with purpuric lesions. Early recognition and treatment are crucial to prevent severe morbidity and mortality.
• Disseminated Intravascular Coagulation (DIC): A condition characterized by both widespread clotting and bleeding, DIC can present with purpura among other symptoms. It is often associated with severe underlying conditions such as sepsis or trauma.
• Thrombotic Thrombocytopenic Purpura (TTP): A rare disorder of the blood-coagulation system, causing extensive microscopic thrombi to form in the smallest blood vessels throughout the body, leading to microangiopathic hemolytic anemia. It's rare in children but can be life-threatening.

Rare Diagnoses

• Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues, which can lead to easy bruising and purpura.
• Scurvy: Caused by vitamin C deficiency, scurvy can lead to purpura due to impaired collagen synthesis affecting blood vessel integrity.
• Leukemia: Certain types of leukemia can present with purpuric lesions due to bone marrow failure and subsequent thrombocytopenia or vasculitis. While rare as a first presentation, it's a critical diagnosis not to miss.