Henoch-Schönlein Purpura (HSP): A form of vasculitis that affects small blood vessels and is characterized by the deposition of IgA immune complexes. It often presents with a macular papular purpuric rash that is non-blanchable, abdominal pain, arthritis, and renal involvement. The rash typically starts on the lower extremities and buttocks.

Infectious Purpura: Caused by bacterial infections such as Neisseria meningitidis (meningococcal purpura) or other pathogens. These infections can lead to a purpuric rash due to the dissemination of bacteria and the resulting vasculitis.
Thrombocytopenic Purpura: Conditions like idiopathic thrombocytopenic purpura (ITP) can cause a non-blanchable rash due to low platelet counts, although the rash is more typically petechial or ecchymotic.
Vasculitis: Other forms of vasculitis, such as microscopic polyangiitis or granulomatosis with polyangiitis, can present with purpuric rashes, though they often have additional systemic symptoms.

Meningococcemia: A life-threatening condition caused by Neisseria meningitidis, characterized by a rapidly progressive purpuric rash, fever, and shock. Early recognition and treatment are crucial.
Disseminated Intravascular Coagulation (DIC): A condition characterized by both widespread clotting and bleeding in the vascular system, which can present with a purpuric rash among other symptoms. It is often associated with severe underlying conditions like 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. It presents with a pentad of thrombocytopenia, microangiopathic hemolytic anemia, renal failure, neurological symptoms, and fever.

Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Some types can lead to easy bruising and purpuric rashes due to fragile blood vessels.
Pseudoxanthoma Elasticum (PXE): A rare genetic disorder that affects the elastic fibers present in the skin, eyes, and cardiovascular system, leading to skin lesions and potential purpuric changes.
Amyloidosis: A condition characterized by the deposition of amyloid (a particular type of protein) in various tissues of the body, which can lead to a variety of symptoms including purpuric rashes, particularly when associated with bleeding or easy bruising.