Autoimmune Encephalitis: Pathophysiology and Imaging Review of an Overlooked Diagnosis

Autoimmune encephalitis is a relatively new category of immune-mediated disease involving the central nervous system that demonstrates a widely variable spectrum of clinical presentations, ranging from the relatively mild or insidious onset of cognitive impairment to more complex forms of encephalopathy with refractory seizure. Due to its diverse clinical features, which can mimic a variety of other pathologic processes, autoimmune encephalitis presents a diagnostic challenge to clinicians. Imaging findings in patients with these disorders can also be quite variable, but recognizing characteristic findings within limbic structures suggestive of autoimmune encephalitis can be a key step in alerting clinicians to the potential diagnosis and ensuring a prompt and appropriate clinical work-up. In this article, we review antibody-mediated encephalitis and its various subtypes with a specific emphasis on the role of neuroimaging in the diagnostic work-up.

Naturally occurring hypothermia is more advantageous than fever in severe forms of lipopolysaccharide- and Escherichia coli-induced systemic inflammation

The natural switch from fever to hypothermia observed in the most severe cases of systemic inflammation is a phenomenon that continues to puzzle clinicians and scientists. The present study was the first to evaluate in direct experiments how the development of hypothermia vs. fever during severe forms of systemic inflammation impacts the pathophysiology of this malady and mortality rates in rats. Following administration of bacterial lipopolysaccharide (LPS; 5 or 18 mg/kg) or of a clinical Escherichia coli isolate (5 × 10(9) or 1 × 10(10) CFU/kg), hypothermia developed in rats exposed to a mildly cool environment, but not in rats exposed to a warm environment; only fever was revealed in the warm environment. Development of hypothermia instead of fever suppressed endotoxemia in E. coli-infected rats, but not in LPS-injected rats. The infiltration of the lungs by neutrophils was similarly suppressed in E. coli-infected rats of the hypothermic group. These potentially beneficial effects came with costs, as hypothermia increased bacterial burden in the liver. Furthermore, the hypotensive responses to LPS or E. coli were exaggerated in rats of the hypothermic group. This exaggeration, however, occurred independently of changes in inflammatory cytokines and prostaglandins. Despite possible costs, development of hypothermia lessened abdominal organ dysfunction and reduced overall mortality rates in both the E. coli and LPS models. By demonstrating that naturally occurring hypothermia is more advantageous than fever in severe forms of aseptic (LPS-induced) or septic (E. coli-induced) systemic inflammation, this study provides new grounds for the management of this deadly condition.

Newborn's fibrinolytic mechanism: components and plasmin generation

Plasminogen activity and antigen, tissue-type plasminogen activator (tPA) activity and antigen, plasminogen activator inhibitor (PAI) activity, and plasmin generation rates were determined in 32 normal newborn plasmas and 25 normal adult plasmas. The newborns showed reduced levels of plasminogen activity and antigen and tPA antigen, and activity, normal levels of PAI activity, and slower plasmin generation rates. The slower generation was shown to be due to the hypoplasminogenemia. The in vitro plasmin generation studies also showed that the newborn needed 11 times the usual concentration of urokinase and 5 times the usual concentration of tPA to achieve the minimal activation rate of the adult.

Hemostatic markers in acute stroke

To assess the time course of thrombosis and fibrinolysis after acute stroke, we measured concentrations of fibrinopeptide A (FpA), B-beta 1-42 peptide (B-beta 1-42), B-beta 15-42 peptide (B-beta 15-42), and crosslinked D-dimer (XDP) in 31 patients at varying times following acute ischemic stroke and in 13 neurologically stable patients with chronic strokes. FpA levels were markedly elevated during the first week after stroke and declined slowly during the first month. Mean FpA levels were not significantly elevated in chronic stroke patients. Mean XDP levels were slightly elevated during the first week and increased during the next 2 weeks after stroke. B-beta 1-42 and B-beta 15-42 levels were not elevated at any time following acute stroke. Our data suggest that fibrin formation greatly exceeds endogenous fibrinolysis during the acute phase of ischemic stroke. Endogenous fibrinolysis develops slowly following stroke. Prolonged elevation of FpA concentration suggests that thrombin activity and fibrin formation continue for up to 4 weeks in some patients with ischemic stroke.

The effect of vitamin E on warfarin-induced vitamin K deficiency

Vitamin K-deficient animals and humans developed a more severe coagulopathy when treated with vitamin E, which was due to further reduction in the vitamin K-dependent coagulation factors (II, VII, IX, and X). This phenomenon was not seen in normal vitamin K-sufficient animals or human subjects. The mechanism by which vitamin E causes this effect is not known. These coagulation factors are produced by the liver in precursor forms and are converted to functional proteins by a vitamin K-dependent reaction. Analysis of one of these coagulation factors, prothrombin (factor II), in plasma of vitamin K-deficient animals and humans treated with vitamin E was done in this study. The precursor of factor II is antigenically similar to biologically active factor II and can be activated to form thrombin by Echis carinatus venom. The data showed that functional factor II coagulant activity was reduced below base in warfarin-treated humans and animals given vitamin E. Factor II antigen as determined by electroimmunoassay in humans and factor II coagulant activity as measured using Echis venom in animals were unchanged and no different from untreated controls. The data suggest that vitamin E acts at the vitamin K-carboxylase step of carboxylation of precursor prothrombin and not in the synthesis of the precursor protein.

Effect of polymyxin B sulfate on endotoxin activity in a gram-negative septicemia model

The antiendotoxin effect of polymyxin B was investigated in experimentally induced septicemia in rabbits. The Pasteurella multocida organisms were sensitive to the antibacterial action of penicillin but not to polymyxin B. Animals pre-treated with polymyxin showed positive blood cultures and significantly reduced plasma endotoxin levels (Limulus test) with normal white blood cell and platelet counts when analyzed 6 hr after the injection of live organisms. Polymyxin therapy given after the animals had established septicemia-endotoxemia reduced the plasma endotoxin levels and improved the survival, but had no effect on the leukopenia and thrombocytopenia. The best survival data were obtained in rabbits who were treated with both penicillin and polymyxin. The data suggest that polymyxin is effective in neutralizing the endotoxic effects from live organisms and that the timing and perhaps duration of the polymyxin treatment is of critical importance. In addition, a modified Limulus lysate method was developed which showed that quantitative plasma endotoxin determination could be made more sensitive by prior heating of the plasma to remove the natural inhibitors.

Neonatal thrombosis and the thrombolytic system: pathophysiology and therapy

In older children and adults the use of thrombolytic drugs appears to be a promising medical approach to thromboembolic disease. However, experience in newborns is limited, with both failure and success having been reported. In this article, the fibrinolytic mechanism is delineated. The similarities and differences in this mechanism between newborns and adults are indicated. It is clear that our understanding of the newborn's fibrinolytic system is limited. Thrombolytic therapy is reviewed. It is recommended that future clinical studies be designed to include three essential features: (a) a uniform clinical staging, (b) a dose-response relationship with a plasminogen activator based on in vivo and in vitro studies, and (c) detailed studies of the newborn's fibrinolytic mechanism before and during thrombolytic therapy.

Effect of vitamin E on prothrombin levels in warfarin-induced vitamin K deficiency

Rats rendered lightly vitamin K deficient with warfarin (0.01 mg/100 g, IP) and given the equivalent of 1000 units of vitamin E/kg IM for 7 days, showed a marked reduction in functional factor II activity, but normal factor II levels using Echis venom on coagulation analysis. In 12 humans receiving warfarin, vitamin E was administered in doses of 100 or 400 units/day orally for 4 wk. The results in these patients showed no significant change in the prothrombin time, factor II coagulant activity, or factor II antigen (by electroimmunoassay). However, by using a ratio of factor II coagulant activity to immunoreactive protein, significant reduction was observed when compared to pretreatment ratios. These data suggest that vitamin E acts at the step mediated by vitamin K and not in the synthesis of the factor II precursor. Although the administration of high doses of vitamin E in animals, and possibly humans, with vitamin K deficiency potentiates the vitamin K deficiency, this effect is not clinically obvious with 400 IU/day or less.

Eosinophilia in premature infants: relationship to weight gain

Serial eosinophil counts were determined in 38 hospitalized, appropriately grown premature infants whose gestational ages ranged from 27 to 35 weeks. Absolute eosinophilia (greater than 700/mm3) was documented in 76% (29/38). Eosinophilia was mild (700 to 999/mm3) in 9, moderate (1,000 to 2,999/mm3) in 17, and marked (greater than or equal to 3,000/mm3) in 3 patients. The average time of onset was day 19. Peak eosinophilia was usually seen within one week of onset and lasted an average of 16 days. A consistent relationship (r = 0.86) was found between the day of peak eosinophilia (mean = day 27) and the day on which birthweight was regained (mean = day 22). No association was apparent between the occurrence or degree of eosinophilia and gestational age, birth stress, presence of umbilical catheter, parenteral alimentation solution, and time of beginning or type or oral feeds. The data suggest that eosinophilia is strongly associated with the establishment of an anabolic state.

Iron and the exclusively breast-fed infant from birth to six months

This study was designed to determine whether normal, full-term, exclusively breast-fed infants develop iron deficiency anemia, as defined by hemoglobin or red blood cell indices more than two standard deviations below the age-specific mean, or depletion of iron stores, as defined by an abnormally low serum ferritin level. Thirty-three breast-fed infants were followed from birth to 6 months. Maternal blood and cord blood at delivery, and venous blood from the infants at 2, 4, and 6 months were analyzed for anemia as defined above. At 6 months of age, the mean hemoglobin concentration of these infants was slightly higher than the normal mean; four of 33 infants (12%) had a mean corpuscular volume greater than 2 SD below the reported normal mean; and two of 33 infants (6%) had a serum ferritin level less than 12 ng protein/ml. These data suggest that the infant who is exclusively breast-fed for the first 6 months of life is not at high risk for the development of iron deficiency anemia or the depletion of iron stores during that time.

Thermoregulatory correlates of nausea in rats and musk shrews

Nausea is a prominent symptom and major cause of complaint for patients receiving anticancer chemo- or radiation therapy. The arsenal of anti-nausea drugs is limited, and their efficacy is questionable. Currently, the development of new compounds with anti-nausea activity is hampered by the lack of physiological correlates of nausea. Physiological correlates are needed because common laboratory rodents lack the vomiting reflex. Furthermore, nausea does not always lead to vomiting. Here, we report the results of studies conducted in four research centers to investigate whether nausea is associated with any specific thermoregulatory symptoms. Two species were studied: the laboratory rat, which has no vomiting reflex, and the house musk shrew (Suncus murinus), which does have a vomiting reflex. In rats, motion sickness was induced by rotating them in their individual cages in the horizontal plane (0.75 Hz, 40 min) and confirmed by reduced food consumption at the onset of dark (active) phase. In 100% of rats tested at three centers, post-rotational sickness was associated with marked (~1.5°C) hypothermia, which was associated with a short-lasting tail-skin vasodilation (skin temperature increased by ~4°C). Pretreatment with ondansetron, a serotonin 5-HT3 receptor antagonist, which is used to treat nausea in patients in chemo- or radiation therapy, attenuated hypothermia by ~30%. In shrews, motion sickness was induced by a cyclical back-and-forth motion (4 cm, 1 Hz, 15 min) and confirmed by the presence of retching and vomiting. In this model, sickness was also accompanied by marked hypothermia (~2°C). Like in rats, the hypothermic response was preceded by transient tail-skin vasodilation. In conclusion, motion sickness is accompanied by hypothermia that involves both autonomic and thermoeffector mechanisms: tail-skin vasodilation and possibly reduction of the interscapular brown adipose tissue activity. These thermoregulatory symptoms may serve as physiological correlates of nausea.

The association of maternal and neonatal thrombocytopenia in high-risk pregnancies

In this study of 136 women with pre-eclampsia, eclampsia, placenta previa, or abruptio placentae, 21 mothers were noted to have thrombocytopenia. Seventeen of the 21 were in the pre-eclampsia group. Of the 21 thrombocytopenic mothers, nine were associated with thrombocytopenia in the children, seven children had normal platelet counts, and five had no counts performed. Eight of the nine thrombocytopenic neonates were associated with pre-eclampsia in the mother, and five of these were not believed to have disseminated intravascular coagulation as the etiology of the platelet defect. The results suggest that thrombocytopenia is common in high-risk pregnancies in both the mother and the baby. However, the etiology of the platelet defect cannot be easily explained on the basis of a hypercoagulable state.

Envenomation by the northern blacktail rattlesnake (Crotalus molossus molossus): report of two cases and the in vitro effects of the venom on fibrinolysis and platelet aggregation

In two cases of human envenomation by the northern blacktail rattlesnake (Crotalus molossus molossus) there was marked swelling and ecchymosis of the bitten extremity and thrombocytopenia and, in one case, hypofibrinogenemia. Treatment consisted of i.v. antivenin, crystalloid solution, fresh frozen plasma and cryoprecipitates, with recovery in each case. In vitro studies showed that the venom had fibrinolytic and platelet aggregating properties; a coagulant effect, although present, was much less marked.

Hypometabolism and hypothermia in the rat model of endotoxic shock: independence of circulatory hypoxia

We tested the hypothesis that development of hypothermia instead of fever in endotoxic shock is consequential to hypoxia. Endotoxic shock was induced by bacterial lipopolysaccharide (LPS, 500 μg kg(-1) i.v.) in rats at an ambient temperature of 22 °C. A β3-adrenergic agonist known to activate metabolic heat production, CL316,243, was employed to evaluate whether thermogenic capacity could be impaired by the fall in oxygen delivery (ḊO2) during endotoxic shock. This possibility was rejected as CL316,243 (0.15 mg kg(-1) i.v.) evoked similar rises in oxygen consumption (V̇O2) in the presence and absence of endotoxic shock. Next, to investigate whether a less severe form of circulatory hypoxia could be triggering hypothermia, the circulating volume of LPS-injected rats was expanded using 6% hetastarch with the intention of improving tissue perfusion and alleviating hypoxia. This intervention attenuated not only the fall in arterial pressure induced by LPS, but also the associated falls in V̇O2 and body temperature. These effects, however, occurred independently of hypoxia, as they were not accompanied by any detectable changes in NAD(+)/NADH ratios. Further experimentation revealed that even the earliest drops in cardiac output and ḊO2 during endotoxic shock did not precede the reduction in V̇O2 that brings about hypothermia. In fact, ḊO2 and V̇O2 fell in such a synchrony that the ḊO2/V̇O2 ratio remained unaffected. Only when hypothermia was prevented by exposure to a warm environment (30 °C) did an imbalance in the ḊO2/V̇O2 ratio become evident, and such an imbalance was associated with reductions in the renal and hypothalamic NAD(+)/NADH ratios. In conclusion, hypometabolism and hypothermia in endotoxic shock are not consequential to hypoxia but serve as a pre-emptive strategy to avoid hypoxia in this model.

Factor II (prothrombin) levels in cord blood: correlation of coagulant activity with immunoreactive protein

Hypoprothrombinemia occurs in newborn infants, but it is unclear whether this is the result of reduced production of Factor II precursor or a vitamin K deficient state. In this study, 76 cord blood specimens were analyzed for functional factor coagulant activity and levels of Factor II antigen as determined by electroimmunoassay. In 40 normal term infants, CA = 30% +/- 1.6 (mean +/- SEM) and Ag = 44% +/- 2.3; in 17 normal preterm infants CA = 30% +/- 1.0 and Ag = 31% +/- 4.2; and in 50 normal adults CA = 83 +/- 3 and Ag = 91 +/- 4. In the term infants the average ratio of CA:Ag was 0.90 and in the preterm infants 0.96, both values being similar to those in adults and suggesting underproduction of the precursor form. In 19 term infants who experienced complications of pregnancy and/or delivery, the ratio was 0.76; seven of these ratios were less than 0.70 (range 0.40 to 0.69). These data show that hypoprothrombinemia is common in infant cord blood and is most marked in preterm infants. In the normal infants the CA:Ag ratios were normal, suggesting that the hypoprothrombinemia is the result of reduced production of the protein and not of vitamin K deficiency. However, term infants with complications of labor and delivery had reduced CA:Ag ratios that were suggestive of vitamin K deficiency.