Vasculitis: This is often considered the most likely diagnosis for skin purpura, especially when it appears in a resting or dependent distribution. Vasculitis, such as leukocytoclastic vasculitis, can cause inflammation of the blood vessels, leading to purpura.

Thrombocytopenia: A low platelet count can lead to purpura due to the inability of the blood to clot properly. This can be caused by various conditions, including immune thrombocytopenia purpura (ITP), bone marrow failure, or as a side effect of certain medications.
Coagulopathy: Disorders that affect the coagulation cascade, such as hemophilia or liver disease, can also lead to purpura.
Vitamin Deficiencies: Deficiencies in vitamins like C or K can impair collagen synthesis or blood clotting, respectively, leading to purpura.

Meningococcemia: This is a life-threatening infection caused by Neisseria meningitidis, which can present with purpura. It requires immediate medical attention.
Disseminated Intravascular Coagulation (DIC): A condition characterized by both widespread clotting and bleeding in the vascular system, which can lead to purpura among other symptoms.
Henoch-Schönlein Purpura (HSP): A form of vasculitis that affects blood vessels and is often seen in children, presenting with purpura, joint pain, and sometimes kidney involvement.

Amyloidosis: A condition characterized by the deposition of amyloid proteins in various tissues, which can lead to purpura due to the weakening of blood vessel walls.
Ehlers-Danlos Syndrome: A group of genetic disorders that affect the body's connective tissue, leading to highly flexible joints and fragile skin, which can result in easy bruising or purpura.
Scurvy: A disease resulting from vitamin C deficiency, which can cause purpura due to impaired collagen synthesis and blood vessel integrity.