This is perhaps the most common and most serious disorder of coagulation affecting the nervous system. The basic process depends on the release of thromboplastic substances from damaged tissue, resulting in the activation of the coagulation process and the formation of fibrin, in the course of which clotting factors and platelets are consumed. Virtually any mechanism that produces tissue damage can result in the release of tissue thromboplastins into the circulation. Thus, disseminated intravascular coagulation (DIC) complicates a wide variety of clinical conditions—overwhelming sepsis, massive trauma, cardiothoracic surgery, heat stroke, burns, incompatible blood transfusions and other immune complex disorders, diabetic ketoacidosis, leukemia, obstetric complications, cyanotic congenital heart disease, and shock from many causes.
The essential pathologic change in DIC is the occurrence of widespread fibrin thrombi in small vessels, resulting in numerous small infarctions of many organs, including the brain. Sometimes DIC is manifest by a hemorrhagic diathesis in which petechial hemorrhages are situated around small penetrating vessels. In some cases, cerebral hemorrhage is quite extensive, similar to a primary hypertensive hemorrhage. The main reason for the hemorrhage is the consumption of platelets and various clotting factors that occurs during fibrin formation; in addition, fibrin degradation products have anticoagulant properties of their own.
The diffuse nature of the neurologic damage may suggest a metabolic rather than a vascular disorder of the brain. In the absence of a clear metabolic, infective, or neoplastic cause of an encephalopathy, the onset of acute and fluctuating focal neurologic abnormalities or a generalized and sometimes terminal neurologic deterioration during the course of a severe illness should arouse suspicion of DIC, and coagulation factors and fibrin split products should be measured. Platelet counts are invariably depressed and there is evidence of consumption of fibrinogen and other clotting factors, indicated by prolonged prothrombin and partial thromboplastin times.
In the related illness abbreviated as HELLP mentioned earlier in the sections on hypertensive and eclamptic encephalopathy, women with eclampsia develop liver failure and thrombocytopenia; the contribution of this limited form of DIC to the eclamptic effects on the nervous system have not been established (see earlier discussion of eclampsia).
This condition, in which TIAs, or stroke, migraine, and thrombocytopenia in various combinations, occur in young adults, has already been discussed under “Strokes in Children and Young Adults.” Phospholipids are a family of lipoproteins that influence clotting. Some of the phospholipids with which the antibodies react are shared with clotting factors, particularly prothrombin. Autoantibodies directed at the binding protein of phospholipids thereby induce blood clotting. The first of the antibodies to be described were lupus anticoagulant and anticardiolipin. Most classifications of the antiphospholipid syndrome also include the major target of antibodies, β2-glycoprotein 1, a protein that may be necessary for the binding and procoagulant effect of anticardiolipin antibody. For stroke work, the formal criteria for the diagnosis of the syndrome require that an ischemic event be accompanied by the detection of autoantibodies on two occasions at least 6 weeks apart. Approximately one-quarter of patients with lupus have antiphospholipid proteins and up to 6 percent of women with pregnancy complications have the antibodies. Some surveys indicate that it is found in 17 percent of patients with stroke who are under 50 years old.