Cerebral Infarction due to Severe ADAMTS-13 Deficiency with Normal Hematological Parameters: A Cause of Cryptogenic Stroke.

OBJECTIVES: Thrombotic thrombocytopenic purpura (TTP) is a microangiopathy resulting from an inherited or acquired severe deficiency in a disintegrin and metalloproteinase called ADAMTS-13. Acquired or immune TTP is classically described as a pentad of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, fever, renal insufficiency and neurological symptoms. Thrombotic thrombocytopenic purpura has been linked to stroke with the presence of hematologic abnormalities but whether or not severe ADAMTS-13 deficiency can cause stroke without hematological abnormalities is unknown. MATERIALS AND METHODS: As part of routine clinical care, we identified four cases of recurrent stroke attributed to severe deficiency of ADAMTS-13. We also conducted a search of a centralized electronic health record database including all inpatients and outpatient charts at a single academic medical center over the last ten years in an attempt to identify additional cases. RESULTS: Here we present four cases of stroke and severe ADAMTS-13 deficiency where stroke episodes occurred without microangiopathic hemolytic anemia or severe thrombocytopenia. These cases show the need to consider severe ADAMTS-13 deficiency in the setting of recurrent cryptogenic stroke in young patients. CONCLUSIONS AND RELEVANCE: TTP directed therapies may be considered for patients with recurrent stroke who have extremely low ADAMTS-13 levels, even when platelet and hemoglobin values are normal.

Bevacizumab-associated thrombotic microangiopathy treated with eculizumab: A case series and systematic review of the literature.

BACKGROUND: Bevacizumab is a recombinant monoclonal antibody against the vascular endothelial growth factor A (VEGF-A) ligand that is used in the management of various solid malignancies. The adverse effect profiles of angiogenesis inhibitors, such as bevacizumab, have become increasingly well characterized and include renal manifestations such as hypertension, proteinuria, and thrombotic microangiopathy. Eculizumab inhibits terminal-complement activation and is used to treat atypical hemolytic uremic syndrome. There has been growing usage of eculizumab to treat bevacizumab-associated thrombotic microangiopathy. MATERIALS AND METHODS: We performed a systematic review of the literature to identify full-text articles that describe the use of eculizumab for bevacizumab-associated thrombotic microangiopathy. RESULTS: Our systematic review identified 522 unique articles of which 5 were included in the final review. 9 cases, including 2 new cases presented in this review, were identified in which eculizumab was used in the management of bevacizumab-associated thrombotic microangiopathy. Hematologic parameters and kidney function stabilized or improved in all cases, and the 2 patients who required renal replacement therapy were able to discontinue dialysis. CONCLUSIONS: Given the findings of this systematic review, the use of eculizumab in the treatment of bevacizumab-associated thrombotic microangiopathy warrants further study, particularly in severe cases.

Safety of the thrombopoiesis-stimulating agents for the treatment of immune thrombocytopenia.

The thrombopoiesis-stimulating agents (TSAs) are a novel class of drugs for the treatment of chronic immune thrombocytopenia (ITP). Roimplostim and eltrombopag, the first two TSAs to enter clinical use, received regulatory approval in 2008 and stand poised to change the treatment paradigm in ITP. However, important questions regarding the safety of these agents, particularly with long-term use, remain partially unanswered. The primary objective of this article is to review the reported toxicities associated with the TSAs including rebound thrombocytopenia, thrombosis, hepatotoxicity, formation of neutralizing antibodies, bone marrow fibrosis, hematologic malignancy, cataract formation, and common adverse events. The incidence and severity of these toxicities as well as strategies for monitoring patient safety and pharmacovigilance are discussed.

Heterotypic interactions enabled by polarized neutrophil microdomains mediate thromboinflammatory injury.

Selectins and their ligands mediate leukocyte rolling, allowing interactions with chemokines that lead to integrin activation and arrest. Here we show that E-selectin is crucial for generating a secondary wave of activating signals, transduced specifically by E-selectin ligand-1, that induces polarized, activated alpha(M)beta(2) integrin clusters at the leading edge of crawling neutrophils, allowing capture of circulating erythrocytes or platelets. In a humanized mouse model of sickle cell disease, the capture of erythrocytes by alpha(M)beta(2) microdomains leads to acute lethal vascular occlusions. In a model of transfusion-related acute lung injury, polarized neutrophils capture circulating platelets, resulting in the generation of oxidative species that produce vascular damage and lung injury. Inactivation of E-selectin or alpha(M)beta(2) prevents tissue injury in both inflammatory models, suggesting broad implications of this paradigm in thromboinflammatory diseases. These results indicate that endothelial selectins can influence neutrophil behavior beyond its canonical rolling step through delayed, organ-damaging, polarized activation.

Intravenous immunoglobulins reverse acute vaso-occlusive crises in sickle cell mice through rapid inhibition of neutrophil adhesion.

Previous studies using intravital microscopy in a sickle cell disease (SCD) mouse model suggest that adherent white blood cells (WBCs) play a key role in vaso-occlusion by capturing circulating red blood cells (RBCs) in venules. Commercial intravenous immunoglobulin (IVIG) given before the inflammatory stimuli increased microcirculatory blood flow and survival. To mimic the clinical situation in which SCD patients seek medical attention after the onset of symptoms, we developed an in vivo model in which the therapeutic intervention (eg, IVIG) was administered after in the inflammatory challenge. In this setting, IVIG rapidly (<10 minutes) reduced adherent leukocyte numbers and dramatically inhibited interactions between RBCs and WBCs, resulting in improved microcirculatory blood flow and survival of sickle cell "Berkeley" mice. Longer survival correlated positively with blood flow (P=.001) and negatively with the number of adherent leukocytes (P=.001) and RBC-WBC interactions (P=.002). Using multichannel digital fluorescence videomicroscopy, we found that IVIG affected specifically the recruitment of neutrophils. Moreover, further analyses of leukocyte behavior revealed that IVIG significantly increased rolling velocities, indicating that it alters adhesion pathways involved in slow rolling. These data suggest that the potential therapeutic benefits of IVIG in SCD crises should be evaluated in a clinical trial.

Imaging receptor microdomains on leukocyte subsets in live mice.

We present a simple method to identify the recruitment of leukocyte subsets and determine concurrent surface-receptor clustering in live mice. We show that CD45+ F4/80- Gr-1+ neutrophils are robustly recruited in surgery-activated cremasteric venules, whereas adherent CD45+ B220+ B lymphocytes were dominant in bone marrow venules. Most adherent Gr-1+ leukocytes are not firmly stationary but actively migrate on TNF-alpha-activated cremasteric venular endothelium and exhibit marked polarization of surface PSGL-1, but not LFA-1, to the trailing edge.

Sickle cell vaso-occlusion.

The vaso-occlusion model has evolved impressively over the past several decades from polymerization-based concepts to a complex, wide-ranging schema that involves multistep, heterogeneous, and interdependent interactions among sickle erythrocytes (SSRBCs), adherent leukocytes, endothelial cells, plasma proteins, and other factors. Endothelial activation, induced directly or indirectly by the proinflammatory behavior of SSRBCs, is the most likely initiating step toward vaso-occlusion. Given the complexity and dynamic relationships of the potential mechanisms leading to vaso-occlusion, further in vivo studies in relevant sickle cell animal models will most likely yield the greatest advances and promote the development of novel, more effective therapeutic strategies.