Purpura, Schoenlein-Henoch: A systemic non-thrombocytopenic purpura caused by HYPERSENSITIVITY VASCULITIS and deposition of IGA-containing IMMUNE COMPLEXES within the blood vessels throughout the body, including those in the kidney (KIDNEY GLOMERULUS). Clinical symptoms include URTICARIA; ERYTHEMA; ARTHRITIS; GASTROINTESTINAL HEMORRHAGE; and renal involvement. Most cases are seen in children after acute upper respiratory infections.Purpura: Purplish or brownish red discoloration, easily visible through the epidermis, caused by hemorrhage into the tissues. When the size of the discolorization is >2-3 cm it is generally called Ecchymoses (ECCHYMOSIS).Purpura, Thrombocytopenic, Idiopathic: Thrombocytopenia occurring in the absence of toxic exposure or a disease associated with decreased platelets. It is mediated by immune mechanisms, in most cases IMMUNOGLOBULIN G autoantibodies which attach to platelets and subsequently undergo destruction by macrophages. The disease is seen in acute (affecting children) and chronic (adult) forms.Purpura, Thrombotic Thrombocytopenic: An acquired, congenital, or familial disorder caused by PLATELET AGGREGATION with THROMBOSIS in terminal arterioles and capillaries. Clinical features include THROMBOCYTOPENIA; HEMOLYTIC ANEMIA; AZOTEMIA; FEVER; and thrombotic microangiopathy. The classical form also includes neurological symptoms and end-organ damage, such as RENAL FAILURE.Purpura Fulminans: A severe, rapidly fatal reaction occurring most commonly in children following an infectious illness. It is characterized by large, rapidly spreading skin hemorrhages, fever, or shock. Purpura fulminans often accompanies or is triggered by DISSEMINATED INTRAVASCULAR COAGULATION.Purpura, Hyperglobulinemic: Purplish or brownish red discoloration of the skin associated with increase in circulating polyclonal globulins, usually GAMMA-GLOBULINS. This syndrome often occurs on the legs of women aged 20 to 40 years.Plasma Exchange: Removal of plasma and replacement with various fluids, e.g., fresh frozen plasma, plasma protein fractions (PPF), albumin preparations, dextran solutions, saline. Used in treatment of autoimmune diseases, immune complex diseases, diseases of excess plasma factors, and other conditions.Splenectomy: Surgical procedure involving either partial or entire removal of the spleen.Platelet Count: The number of PLATELETS per unit volume in a sample of venous BLOOD.ADAM Proteins: A family of membrane-anchored glycoproteins that contain a disintegrin and metalloprotease domain. They are responsible for the proteolytic cleavage of many transmembrane proteins and the release of their extracellular domain.Antigens, Human Platelet: Human alloantigens expressed only on platelets, specifically on platelet membrane glycoproteins. These platelet-specific antigens are immunogenic and can result in pathological reactions to transfusion therapy.Plasmapheresis: Procedure whereby plasma is separated and extracted from anticoagulated whole blood and the red cells retransfused to the donor. Plasmapheresis is also employed for therapeutic use.Immunoglobulins, Intravenous: Immunoglobulin preparations used in intravenous infusion, containing primarily IMMUNOGLOBULIN G. They are used to treat a variety of diseases associated with decreased or abnormal immunoglobulin levels including pediatric AIDS; primary HYPERGAMMAGLOBULINEMIA; SCID; CYTOMEGALOVIRUS infections in transplant recipients, LYMPHOCYTIC LEUKEMIA, CHRONIC; Kawasaki syndrome, infection in neonates, and IDIOPATHIC THROMBOCYTOPENIC PURPURA.Danazol: A synthetic steroid with antigonadotropic and anti-estrogenic activities that acts as an anterior pituitary suppressant by inhibiting the pituitary output of gonadotropins. It possesses some androgenic properties. Danazol has been used in the treatment of endometriosis and some benign breast disorders.Blood Platelets: Non-nucleated disk-shaped cells formed in the megakaryocyte and found in the blood of all mammals. They are mainly involved in blood coagulation.Hemolytic-Uremic Syndrome: A syndrome that is associated with microvascular diseases of the KIDNEY, such as RENAL CORTICAL NECROSIS. It is characterized by hemolytic anemia (ANEMIA, HEMOLYTIC); THROMBOCYTOPENIA; and ACUTE RENAL FAILURE.Nephritis: Inflammation of any part of the KIDNEY.Rho(D) Immune Globulin: Immunizing agent containing IMMUNOGLOBULIN G anti-Rho(D) used for preventing Rh immunization in Rh-negative individuals exposed to Rh-positive red blood cells.Ecchymosis: Extravasation of blood into the skin, resulting in a nonelevated, rounded or irregular, blue or purplish patch, larger than a petechia.Vasculitis, Leukocytoclastic, Cutaneous: Disorder characterized by a vasculitic syndrome associated with exposure to an antigen such as a drug, infectious agent, or other foreign or endogenous substance. Its pathophysiology includes immune complex deposition and a wide range of skin lesions. Hypersensitivity or allergy is present in some but not all cases.Leg Dermatoses: A nonspecific term used to denote any cutaneous lesion or group of lesions, or eruptions of any type on the leg. (From Stedman, 25th ed)Pregnancy Complications, Hematologic: The co-occurrence of pregnancy and a blood disease (HEMATOLOGIC DISEASES) which involves BLOOD CELLS or COAGULATION FACTORS. The hematologic disease may precede or follow FERTILIZATION and it may or may not have a deleterious effect on the pregnant woman or FETUS.Autoantibodies: Antibodies that react with self-antigens (AUTOANTIGENS) of the organism that produced them.von Willebrand Factor: A high-molecular-weight plasma protein, produced by endothelial cells and megakaryocytes, that is part of the factor VIII/von Willebrand factor complex. The von Willebrand factor has receptors for collagen, platelets, and ristocetin activity as well as the immunologically distinct antigenic determinants. It functions in adhesion of platelets to collagen and hemostatic plug formation. The prolonged bleeding time in VON WILLEBRAND DISEASES is due to the deficiency of this factor.Thrombocytopenia: A subnormal level of BLOOD PLATELETS.Platelet Transfusion: The transfer of blood platelets from a donor to a recipient or reinfusion to the donor.Oklahoma