Case records of the Massachusetts General Hospital. Weekly clinicopathological exercises. Case 30-1991. An 85-year-old woman with renal failure, neurologic deterioration, and seizures

MRI demonstration of a reversible lesion in cerebral deep white matter in thrombotic thrombocytopenic purpura

We report a 75-year-old woman with thrombotic thrombocytopenic purpura (TTP) whose MRI showed diffuse abnormal signal in the deep white matter. She was successfully treated, and this abnormal signal disappeared. This finding indicates that the deep white matter is involved in TTP; the lesion may reflect reversible microangiopathy and brain oedema.

Thrombopoietin: biology, clinical applications, role in the donor setting

Thrombopoietin (c-Mpl ligand) is the hematopoietic growth factor that is responsible for regulating the production of platelets from bone marrow megakaryocytes. This approximately 90 kd protein has recently been isolated and is comprised of an erythropoietin domain that is approximately 50% homologous to erythropoietin and a carbohydrate domain that is highly glycosylated and appears to stabilize the protein in the circulation. Thrombopoietin is produced in the liver and blood levels are determined by the mass of circulating platelets. However, there is no platelet "sensor." Rather platelets contain high affinity thrombopoietin receptors that bind and remove thrombopoietin from the circulation and thereby directly determine circulating levels. In vitro thrombopoietin stimulates both early and late megakaryocyte precursors as well as some erythroid and multipotential progenitor cells. When administered to normal animals, it stimulates platelet production up to six-fold without affecting other lineages. However, when given to animals following chemotherapy or irradiation, it stimulates erythroid and myeloid as well as platelet recovery. Several different recombinant thrombopoietin proteins are now entering clinical trials in humans and all preliminary reports confirm a potent thrombopoietic stimulus and apparent lack of toxicity. Thrombopoietin shows great promise in preventing the thrombocytopenia associated with chemotherapy, bone marrow transplantation, and other acute or chronic thrombocytopenic disorders. In transfusion medicine, thrombopoietin may help mobilize peripheral blood progenitor cells, stimulate donors for plateletpheresis, and enhance platelet survival and function during storage, Many studies are currently underway in all these areas and should soon establish the role of thrombopoietin in clinical medicine.

Southwestern Internal Medicine Conference: Shiga-like toxins in hemolytic-uremic syndrome and thrombotic thrombocytopenic purpura

The majority of cases of hemolytic-uremic syndrome and a smaller proportion of cases of thrombotic thrombocytopenic purpura have recently been shown to result from a toxin produced by enteric bacteria, referred to as verotoxin, or Shiga-like toxin. The predominant toxin-producing bacterial strain in North America is E. coli O157:H7, which causes hemorrhagic colitis in humans after ingestion of contaminated meat. The toxin is believed to gain entry to the circulation from the bowel wall; it then binds to specific glycolipid receptors abundant on renal vascular endothelial cells. The toxin inactivates ribosomes inside the cells, thereby killing them and producing the clinical manifestations of hemolytic-uremic syndrome. Recognition of the etiology of hemolytic-uremic syndrome may lead to better prospects for prevention and treatment.

Hematologic emergencies. Management of hyperleukocytic syndrome, DIC, and thrombotic thrombocytopenic purpura

Three hematologic emergencies are reviewed in this article: the hyperleukocytic syndrome, disseminated intravascular coagulopathy (DIC), and thrombotic thrombocytopenic purpura (TTP). The hyperleukocytic syndrome most commonly occurs in patients with acute myelogenous leukemia. It commonly affects the lungs and may cause intracranial hemorrhage. Long-term control is accomplished only by inducing a remission of the leukemia. Patients with DIC may have excessive clotting, uncontrolled bleeding, or both. Infections are the most common cause; cases in obstetric patients are usually due to abruptio placentae or retained dead fetus. Any acute leukemia can cause DIC. The underlying disorder is the usual cause of death. TTP is thought to be due to a substance or substances in the plasma that initiate marked platelet aggregation in the microcirculation. It affects persons of any age and either sex. Plasmapheresis is the preferred treatment.