Thrombotic thrombocytopenia purpura (TTP) and other thrombotic microangiopathies

Role of von Willebrand factor in venous thromboembolic disease

Objective

Evolving evidence of the shared risk factors and pathogenic mechanisms in arterial and venous thrombosis questions of the strict vascular dichotomy of arterial vs venous. The connection between arterial and venous thrombosis has been highlighted by common underlying inflammatory processes, a concept known as thromboinflammatory disease. Using this relationship, we can apply knowledge from arterial disease to better understand and potentially mitigate venous disease. A protein that has been extensively studied in atherothrombotic disease and inflammation is von Willebrand factor (VWF). Because many predisposing and provoking factors of venous thromboembolism (VTE) have been shown to directly modulate VWF levels, it is, perhaps, not surprising that VWF has been highlighted by several recent association studies of patients with VTE.

Methods

In the present narrative review, we investigated more deeply the effects of VWF in venous disease by synthesizing the data from clinical studies of deep vein thrombosis of the limbs, pulmonary embolism, portal and cerebral vein thrombosis, and the complications of thrombosis, including post-thrombotic syndrome, venous insufficiency, and chronic thromboembolic pulmonary hypertension. We have also discussed the findings from preclinical studies to highlight novel VWF biochemistry in thrombosis and therapeutics.

Results

Across the spectrum of venous thromboembolic disease, we consistently observed that elevated VWF levels conferred an increased risk of VTE and long-term venous complications. We have highlighted important findings from VWF molecular research and have proposed mechanisms by which VWF participates in venous disease. Emerging evidence from preclinical studies might reveal novel targets for thromboinflammatory disease, including specific VWF pathophysiology. Furthermore, we have highlighted the utility of measuring VWF to prognosticate and risk stratify for VTE and its complications.

Conclusions

As the prevalence of inflammatory processes, such as aging, obesity, and diabetes increases in our population, it is critical to understand the evolving role of VWF in venous disease to guide clinical decisions and therapeutics.

Thrombotic Thrombocytopenic Purpura in Interferon Beta-1a-Treated Patient Diagnosed with Relapsing-Remitting Multiple Sclerosis: A Case Report

Background: Secondary thrombotic thrombocytopenic purpura (TTP) due to interferon beta-1a intramuscular (im) treatment is an uncommon adverse effect with only a few cases in multiple sclerosis patients reported worldwide. TTP together with haemolytic uremic syndrome (HUS) are classic forms of thrombotic microangiopathy, characterized by small-vessel platelet micro-thrombi that manifest clinically in a similar manner. Most common signs and symptoms include bruises and ecchymosis, neurologic symptoms and renal impairment. Interferon beta-1a represents one of the first-line therapies for relapsing-remitting multiple sclerosis due to its accessibility and efficacy. Case presentation: A 36-year-old woman who was previously diagnosed with relapsing-remitting multiple sclerosis had received weekly intramuscular injections with beta-interferon-1a (Avonex 30 mcg). After 9 months of treatment, she presented bruises and ecchymosis on her limbs and torso, epistaxis, gingival bleeding aggravated within 48 h and a persistent headache that was non-responsive to common analgesics. Haematology tests revealed typical results for thrombotic microangiopathy, including severe thrombocytopenia (4000/mm³) and microangiopathic haemolytic anaemia with frequent schistocytes on the peripheral blood smear. Once the beta-interferon administration was ceased and upon the initiation of methylprednisolone, the symptoms remitted. Conclusions: In this case study, we portrayed the particular association between the remission phase of multiple sclerosis and the violent onset of interferon-induced thrombotic thrombocytopenic purpura.

Primary Immunodeficiency and Thrombocytopenia

Primary immunodeficiency (PID) or Inborn errors of immunity (IEI) refers to a heterogeneous group of disorders characterized by immune system impairment. Although patients with IEI manifest highly variable symptoms, the most common clinical manifestations are recurrent infections, autoimmunity and malignancies. Some patients present hematological abnormality including thrombocytopenia due to different pathogenic mechanisms. This review focuses on primary and secondary thrombocytopenia as a complication, which can occur in IEI. Based on the International Union of Immunological Societies phenotypic classification for IEI, the several innate and adaptive immunodeficiency disorders can lead to thrombocytopenia. This review, for the first time, describes manifestation, mechanism and therapeutic modalities for thrombocytopenia in different classes of IEI.

Extracellular DNA-A Danger Signal Triggering Immunothrombosis

Clotting and inflammation are effective danger response patterns positively selected by evolution to limit fatal bleeding and pathogen invasion upon traumatic injuries. As a trade-off, thrombotic, and thromboembolic events complicate severe forms of infectious and non-infectious states of acute and chronic inflammation, i.e., immunothrombosis. Factors linked to thrombosis and inflammation include mediators released by platelet granules, complement, and lipid mediators and certain integrins. Extracellular deoxyribonucleic acid (DNA) was a previously unrecognized cellular component in the blood, which elicits profound proinflammatory and prothrombotic effects. Pathogens trigger the release of extracellular DNA together with other pathogen-associated molecular patterns. Dying cells in the inflamed or infected tissue release extracellular DNA together with other danger associated molecular pattern (DAMPs). Neutrophils release DNA by forming neutrophil extracellular traps (NETs) during infection, trauma or other forms of vascular injury. Fluorescence tissue imaging localized extracellular DNA to sites of injury and to intravascular thrombi. Functional studies using deoxyribonuclease (DNase)-deficient mouse strains or recombinant DNase show that extracellular DNA contributes to the process of immunothrombosis. Here, we review rodent models of immunothrombosis and the evolving evidence for extracellular DNA as a driver of immunothrombosis and discuss challenges and prospects for extracellular DNA as a potential therapeutic target.

Expert statement on the ICU management of patients with thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is fatal in 90% of patients if left untreated and must be diagnosed early to optimize patient outcomes. However, the very low incidence of TTP is an obstacle to the development of evidence-based clinical practice recommendations, and the very wide variability in survival rates across centers may be partly ascribable to differences in management strategies due to insufficient guidance. We therefore developed an expert statement to provide trustworthy guidance about the management of critically ill patients with TTP. As strong evidence was difficult to find in the literature, consensus building among experts could not be reported for most of the items. This expert statement is timely given the recent advances in the treatment of TTP, such as the use of rituximab and of the recently licensed drug caplacizumab, whose benefits will be maximized if the other components of the management strategy follow a standardized pattern. Finally, unanswered questions are identified as topics of future research on TTP.

Heparin-induced thrombocytopenia associated with thrombotic microangiopathy

Some cases of thrombotic microangiopathy (TMA) are refractory to plasma exchange therapy (PE) with persistence or recurrence of thrombocytopenia. We report two patients suffering from TMA of different aetiologies (associated with disseminated malignancy, typical haemolytic uraemic syndrome) with recurrent or persistent thrombocytopenia despite adequate therapy including PE. Since both patients were exposed to unfractionated heparin, heparin-induced thrombocytopenia (HIT) was suspected as a cause. Pretest probabilities for HIT were intermediate. ELISA for PF4/heparin antibodies was strongly positive in both cases, and HIT was confirmed by heparin-induced platelet activation assay. Anticoagulation with lepirudin was initiated, with subsequent rapid increase of the platelet count.

TMA might represent a predisposition for HIT. This could be due to TMA-related platelet activation with increased PF4 release. In TMA patients exposed to heparin and with refractory or rapidly recurrent thrombocytopenia HIT should always be considered as a possible cause.

Relapsing thrombotic microangiopathy and intravenous sustained-release oxycodone

Thrombotic microangiopathy (TMA) associated with injecting sustained-release oxymorphone, an opioid intended for oral use, has previously been reported. We report a case of TMA secondary to intravenous use of sustained-release oxycodone, and the first case to demonstrate relapsing disease due to persistent intravenous opioid use. In cases such as these, TMA is suspected to be due to a polyethylene oxide (PEO) coating found on these drugs, and the disease is likely due to a directly toxic effect of PEO to endothelial cells. We hypothesize that there are unidentified genetic predispositions causing some persons to be susceptible to developing this disease.

ADAMTS13 gene variants and function in women with preeclampsia: a population- based nested case- control study from the HUNT Study

INTRODUCTION

Known genetic variants with reference to preeclampsia only explain a proportion of the heritable contribution to the development of this condition. The association between preeclampsia and the risk of cardiovascular disease later in life has encouraged the study of genetic variants important in thrombosis and vascular inflammation also in relation to preeclampsia. The von Willebrand factor-cleaving protease, ADAMTS13, plays an important role in micro vascular thrombosis, and partial deficiencies of this enzyme have been observed in association with cardiovascular disease and preeclampsia. However, it remains unknown whether decreased ADAMTS13 levels represent a cause or an effect of the event in placental and cardiovascular disease.

METHODS

We studied the distribution of three functional genetic variants of ADAMTS13, c.1852C>G (rs28647808), c.4143_4144dupA (rs387906343), and c.3178C>T (rs142572218) in women with preeclampsia and their controls in a nested case-control study from the second Nord-Trøndelag Health Study (HUNT2). We also studied the association between ADAMTS13 activity and preeclampsia, in serum samples procured unrelated in time of the preeclamptic pregnancy.

RESULTS

No differences were observed in genotype, allele or haplotype frequencies of the different ADAMTS13 variants when comparing cases and controls, and no association to preeclampsia was found with lower levels of ADAMTS13 activity.

CONCLUSION

Our findings indicate that ADAMTS13 variants and ADAMTS13 activity do not contribute to an increased risk of preeclampsia in the general population.

ADAMTS-13 in the Diagnosis and Management of Thrombotic Microangiopathies

Thrombotic microangiopathies (TMAs) comprise a group of distinct disorders characterized by microangiopathic hemolytic anemia, thrombocytopenia, and microvascular thrombosis. For many years distinction between these TMAs, especially between thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), remained purely clinical and hard to make. Recent discoveries shed light on different pathogenesis of TTP and HUS. Ultra-large von Willebrand factor (UL-VWF) platelet thrombi, resulting from the deficiency of cleavage protease which is now known as ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), were found to cause TTP pathology, while Shiga toxins or abnormalities in regulation of the complement system cause microangiopathy and thrombosis in HUS. TMAs may appear in various conditions such as pregnancy, inflammation, malignancy, or exposure to drugs. These conditions might cause acquired TTP, HUS, or other TMAs, or might be a trigger in individuals with genetic predisposition to ADAMTS-13 or complement factor H deficiency. Differentiation between these TMAs is highly important for urgent initiation of appropriate therapy. Measurement of ADAMTS-13 activity and anti-ADAMTS-13 antibody levels may advance this differentiation resulting in accurate diagnosis. Additionally, assessment of ADAMTS-13 levels can be a tool for monitoring treatment efficacy and relapse risk, allowing consideration of therapy addition or change. In the past few years, great improvements in ADAMTS-13 assays have been made, and tests with increased sensitivity, specificity, reproducibility, and shorter turnaround time are now available. These new assays enable ADAMTS-13 measurement in routine clinical diagnostic laboratories, which may ultimately result in improvement of TMA management.

Gemcitabine-related thrombotic microangiopathy: a single-centre retrospective series

INTRODUCTION

Thrombotic microangiopathy (TMA) has been reported as a complication of chemotherapy. Many antineoplastic agents have been linked to TMA, gemcitabine being one of the most frequently cited as related to this syndrome.

METHODS

A retrospective search for chemotherapy-induced TMA cases among gemcitabine users in a single oncology centre from January 2009 to September 2012 was performed.

RESULTS

Three cases of gemcitabine-induced TMA were reported, from a total of 264 patients (incidence: 1·13%) who received the drug. From the three cases reported, two (66%) patients died as a consequence of the syndrome.

DISCUSSION

These findings are compatible with previous analyses, which report an incidence of gemcitabine-associated TMA ranging from 0·008 to 2·2% and mortality rates from 15 to 90%. Unlike previously reported, however, cumulative dose was not predictive of risk.

CONCLUSION

Gemcitabine-induced TMA is an underdiagnosed condition characterized by high mortality rates. Attention should be called for a higher level of awareness to provide early diagnosis and proper treatment.

"Almost bleeding to death": the conundrum of acquired amegakaryocytic thrombocytopenia

Acquired amegakaryocytic thrombocytopenia (AAT) is a rare hematological disorder causing severe thrombocytopenia and bleeding. Previous in vitro studies postulated both cell-mediated suppression of megakaryocytopoiesis in early megakaryocytic progenitor cells and humoral-mediated suppression by anti-thrombopoietin antibodies as possible etiologies of AAT. Patients with AAT usually present with severe bleeding and thrombocytopenia that is unresponsive to steroids and intravenous immunoglobulin (IVIG). Although standard guidelines have not been established for management of AAT, a few case reports have indicated a response to immunosuppressive treatment. The prompt recognition of this disease entity is essential in view of the substantial risk of morbidity and mortality from excessive bleeding. We report a case of AAT successfully treated with equine antithymocyte globulin (ATG) and cyclosporine (CSP).

Thrombotic thrombocytopenic purpura and other thrombotic microangiopathic hemolytic anemias: diagnosis and classification

Thrombotic microangiopathies (TMAs) include several diseases, most prominently are thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS). TMAs are characterized by profound thrombocytopenia, microangiopathic hemolytic anemia and organ ischemia. In most cases TTP results from deficiency of ADAMTS13, the von Willebrand factor-cleaving protease leading to increase of ultra-large von Willebrand factor (ULVWF) multimers. Congenital TTP is due to mutations in the gene of ADAMTS13 whereas acquired TTP is due to production of autoantibodies against ADAMTS13. In both cases severe deficiency of ADAMTS13 exists. However, the presence of ADAMTS13 activity does not rule out TTP. Diagnostic criteria of TTP are based on clinical features of neurologic and renal disfunction along with anemia and thrombocytopenia, low ADAMTS13 activity, and the presence of ULVWF. The standard treatment of TTP includes plasma exchange, protein A immunoabsobtion, immunosuppressive drugs, CD20 antibodies against B cells, and splenectomy. HUS is commonly caused by infection with Shiga-toxin produced by Escherichia coli. HUS is characterized by thrombocytopenia, anemia, renal impairment and diarrhea. Rarely, atypical HUS appears as a consequence of mutations related to the alternative pathway for the compliment system. Plasmapheresis in HUS is not efficient. Alternatively, plasma therapy and in some cases dialysis are used. TMA diseases may be associated with other infections, bone marrow transplantation, pregnancy, systemic vasculitis, and certain drugs.

Tacrolimus-induced thrombotic microangiopathy in orthotopic liver transplant patients: case series of four patients

Thrombotic microangiopathy (TMA) is a potentially fatal complication in solid organ and bone marrow transplant patients, with reported incidence of 0.5-3% and mortality of about 75%. To emphasise the importance of early diagnosis and prompt commencement of therapy results in improved clinical outcomes. A retrospective study of all patients who underwent orthotopic liver transplantation (OLTX) at the Western Australian Liver Transplantation Service from May 1994 to December 2010 was conducted to identify patients who developed tacrolimus-induced TMA. We identified four patients with tacrolimus-induced TMA post-OLTX, derived from a cohort of 104 patients treated with tacrolimus in our institution. The mean age at diagnosis was 40 years, and the mean time of onset was 63 ± 7.5 weeks after OLTX. The indications for OLTX in the four patients were fulminant hepatic failure in three (Wilson disease, paracetamol overdose and post-partum thrombotic thrombocytopenic purpura) and hepatitis C virus-related cirrhosis. All patients had tacrolimus post-OLTX. At diagnosis, tacrolimus was discontinued in all patients, and three of the four patients underwent plasma exchange and all patients improved clinically. Mean duration of follow up was 15 ± 7.5 months. There was no mortality 6 months post-TMA. Early diagnosis with immediate discontinuation or conversion of calcineurin inhibitors and plasma exchange should be offered to OLTX patients with TMA as it results in good outcomes.

Pregnancy-Associated Kidney Injury

A 23-year-old G1P0000 without prior past medical history is 31 weeks pregnant with prenatal care presents with complaints of worsening leg and face swelling for the past 2 days now seeks care because of headache, diarrhea, nausea, and vomiting. On exam she is found to have a blood pressure of 120/86, edema, and brisk deep tendon reflexes. Laboratory testing revealed hemoglobin 11.3 g/dl, platelet count 141,000/μl white blood count 18,000/μl, creatinine 1.1 mg/dl, aspartate aminotransferases (AST) 65 U/l, lactate dehydrogenase (LDH) 400 U/l, total bilirubin 1.1 mg/dl, prothrombin time (PT) 14.7 s, ammonia of 90 mcg/dl, blood glucose 139 mg/dl, calcium 7.3 mg/dl, and uric acid of 6.0 mg/dl. The urinalysis demonstrated WBC’s 3–5/hpf, RBC’s 3–5/hpf—non-dysmorphic, renal tubular epithelial cells were seen and a urine protein to creatinine ratio of 2. One day after hospitalization the patient’s blood pressure was 145/87 with a similar blood pressure 6 h later.

New Fundamentals in Hemostasis

Hemostasis encompasses the tightly regulated processes of blood clotting, platelet activation, and vascular repair. After wounding, the hemostatic system engages a plethora of vascular and extravascular receptors that act in concert with blood components to seal off the damage inflicted to the vasculature and the surrounding tissue. The first important component that contributes to hemostasis is the coagulation system, while the second important component starts with platelet activation, which not only contributes to the hemostatic plug, but also accelerates the coagulation system. Eventually, coagulation and platelet activation are switched off by blood-borne inhibitors and proteolytic feedback loops. This review summarizes new concepts of activation of proteases that regulate coagulation and anticoagulation, to give rise to transient thrombin generation and fibrin clot formation. It further speculates on the (patho)physiological roles of intra- and extravascular receptors that operate in response to these proteases. Furthermore, this review provides a new framework for understanding how signaling and adhesive interactions between endothelial cells, leukocytes, and platelets can regulate thrombus formation and modulate the coagulation process. Now that the key molecular players of coagulation and platelet activation have become clear, and their complex interactions with the vessel wall have been mapped out, we can also better speculate on the causes of thrombosis-related angiopathies.

Delayed visual recovery in pregnancy-associated thrombotic thrombocytopenic purpura with bilateral serous retinal detachment

BACKGROUND

To present a pregnancy-associated thrombotic thrombocytopenic purpura (TTP) patient with bilateral serous retinal detachment (SRD).

METHODS

Case report.

RESULTS

A 28-year-old nulliparous woman with 31 weeks gestation was presented to the local hospital with preeclampsia, hemolytic anemia, thrombocytopenia and bilateral blurry vision. Funduscopic examination showed bilateral macular SRD. Within the first month after delivery of a live female baby via cesarean section (at 32 weeks gestation), the patient experienced a recurrent course of hemolytic anemia and thrombocytopenia, and was then transferred to our hospital. On admission, her best corrected visual acuity (BCVA) was 0.1 OU; optical coherence tomography (OCT) confirmed the presence of bilateral macular SRD; electroretinography (ERG) examination showed diminished rod responses with reduced a and b waves in cone and mixed rod-cone responses. She was ultimately diagnosed with TTP and was treated systemically with fresh frozen plasma, rituximab, prednisone and cyclophosphamide. Despite persistent visual disturbances, she was discharged 1 month after admission with stabilization of systemic manifestations. At her first follow-up visit 6 months after discharge, surprisingly, her BCVA had improved to 1.0 OU; fundus examination and OCT confirmed the complete resolution of bilateral macular SRD and ERG revealed subnormal (right) and normal (left) electrophysiological responses. We believe that in this case, the clinical context (pregnancy) in which TTP developed, the unreported ERG characteristics and the unexpected delayed visual recovery are worth reporting.

CONCLUSIONS

TTP should be considered as a potential differential diagnosis in patients with pregnancy-associated SRD. Appropriate systemic treatment might be mandatory for visual recovery.

Antibody mediated rejection associated with complement factor h-related protein 3/1 deficiency successfully treated with eculizumab

Antibody mediated rejection (AMR) activates the classical complement pathway and can be detrimental to graft survival. AMR can be accompanied by thrombotic microangiopathy (TMA). Eculizumab, a monoclonal C5 antibody prevents induction of the terminal complement cascade (TCC) and has recently emerged as a therapeutic option for AMR. We present a highly sensitized 13-year-old female with end-stage kidney disease secondary to spina bifida-associated reflux nephropathy, who developed severe steroid-, ATG- and plasmapheresis-resistant AMR with TMA 1 week post second kidney transplant despite previous desensitization therapy with immunoglobulin infusions. Eculizumab rescue therapy resulted in a dramatic improvement in biochemical (C3; creatinine) and hematological (platelets) parameters within 6 days. The patient was proven to be deficient in complement Factor H-related protein 3/1 (CFHR3/1), a plasma protein that regulates the complement cascade at the level of C5 conversion and has been involved in the pathogenesis of atypical hemolytic uremic syndrome caused by CFH autoantibodies (DEAP-HUS). CFHR1 deficiency may have worsened the severe clinical progression of AMR and possibly contributed to the development of donor-specific antibodies. Thus, screening for CFHR3/1 deficiency should be considered in patients with severe AMR associated with TMA.

Successful sirolimus rescue in tacrolimus-induced thrombotic microangiopathy after living-related liver transplantation

TMA is a rare complication of tacrolimus. Disruption of endothelial cells, platelet aggregation, and intravascular mechanical fragmentation of red cells are core mechanisms of injury; however, exact pathways of toxicity are not clear. The clinical presentation may vary but TMA is a potentially life-threatening condition usually demanding aggressive treatment. We present the case of TMA in a child after living-related liver transplantation (LRLTx) on tacrolimus-based immunosuppressive regiment successfully converted to sirolimus.

Thrombotic microangiopathy with skin localization secondary to cytarabine-daunorubicin association: report of a case

The thrombotic microangiopathy is a syndrome characterized by the combination of mechanical hemolytic anemia, peripheral thrombocytopenia, and organ failure of variable severity. In addition to the idiopathic form, several cases are identified as secondary to pregnancy, infections, disease systems, organ transplants, and cancer. Other forms are secondary to drugs including antimitotics. We report the case of a patient followed for acute myelogenous leukemia. She received induction chemotherapy combining daunorubicin and cytarabine, complicated by thrombotic thrombocytopenic purpura.

Shiga toxin pathogenesis: kidney complications and renal failure

The kidneys are the major organs affected in diarrhea-associated hemolytic uremic syndrome (D(+)HUS). The pathophysiology of renal disease in D(+)HUS is largely the result of the interaction between bacterial virulence factors such as Shiga toxin and lipopolysaccharide and host cells in the kidney and in the blood circulation. This chapter describes in detail the current knowledge of how these bacterial toxins may lead to kidney disease and renal failure. The toxin receptors expressed by specific blood and resident renal cell types are also discussed as are the actions of the toxins on these cells.

Viral-associated thrombotic microangiopathies

Thrombotic microangiopathies encompass a group of disorders characterized by microangiopathic hemolytic anemia, thrombocytopenia associated with hyaline thrombi (comprised primarily of platelet aggregates in the microcirculation), and varying degrees of end-organ failure. Many primary (genetic) and secondary etiological predisposing factors have been described-namely pregnancy, autoimmune disorders, cancer, drugs and antineoplastic therapy, bone marrow transplantation/solid organ transplantation, and infections. In the setting of infectious diseases, the association with Shiga or Shiga-like exotoxin of Escherichia coli 0157:h7 or Shigella dysenteriae type 1-induced typical hemolytic uremic syndrome is well known. Recently however, an increasing body of evidence suggests that viruses may also play an important role as trigger factors in the pathogenesis of thrombotic microangiopathies. This is a comprehensive review focusing on the current understanding of viral associated/induced endothelial stimulation and damage that ultimately leads to the development of this life-threatening multisystemic disorder.

Novel developments in thrombotic microangiopathies: is there a common link between hemolytic uremic syndrome and thrombotic thrombocytic purpura?

Thrombotic microangiopathies (TMA) represent a spectrum of related disorders associated with newly formed thrombi that block perfusion and thus affect the function of either renal or neurological organs and tissue. Recent years have seen a dramatic development in the field of TMA and for the two major forms hemolytic uremic syndrome (HUS) and thrombocytopenic purpura (TTP), new genetic causes and also autoimmune forms have been identified. This development indicates a similar pathophysiology and suggests that the two acute disorders are based on common principles. HUS is primarily a kidney disease and TTP also develops in the kidney and at neurological sites. In HUS thrombi formation is likely due to a deregulated complement activation and inappropriate platelet activity. In TTP thrombi formation occurs because of inappropriate processing of released multimers of von Willebrand Factor (vWF). Defining both the similarities and the unique features of each disorder will open up new ways and concepts that are relevant for diagnosis, for therapy, and for the prognostic outcome of kidney transplantations. Here we summarize the most relevant topics and timely issues that were presented and discussed at the 4th International Workshop on Thrombotic Microangiopathies held in Weimar in October 2009 (www.hus-ttp.de).

Novel nephrotoxins

Drug and xenobiotic toxicity is an important cause of kidney injury, especially in vulnerable patients. Nephrotoxic syndromes include functional disorders; vascular injury, such as thrombotic microangiopathy; glomerular injury resulting in nephrotic syndrome or glomerulonephritis; acute tubular necrosis; acute interstitial nephritis; and crystalopathy/nephrolithiasis. Recently reported nephrotoxins are reviewed in the context of these syndromes of kidney injury.

Advances in our understanding of the pathogenesis of glomerular thrombotic microangiopathy

Glomerular thrombotic microangiopathy is a hallmark feature of haemolytic uraemic syndrome, the leading cause of acute renal failure in childhood. This paper is a review of the different mechanistic pathways that lead to this histological picture in the kidney. It will focus on atypical HUS and complement dysregulation, but will also highlight some other recent advances in our understanding of this condition, including the potential role of the molecule vascular endothelial growth factor-A (VEGF-A).

Renal involvement in preeclampsia: similarities to VEGF ablation therapy

Glomerular VEGF expression is critical for the maintenance and function of an intact filtration barrier. Alterations in glomerular VEGF bioavailability result in endothelial as well as in podocyte damage. Renal involvement in preeclampsia includes proteinuria, podocyturia, elevated blood pressure, edema, glomerular capillary endotheliosis, and thrombotic microangiopathy. At least the renal signs, symptoms, and other evidence can sufficiently be explained by reduced VEGF levels. The aim of this paper was to summarize our pathophysiological understanding of the renal involvement of preeclampsia and point out similarities to the renal side effects of VEGF-ablation therapy.

Dangerous drug interactions leading to hemolytic uremic syndrome following lung transplantation

Background

To report our experience of a rather uncommon drug interaction, resulting in hemolytic uremic syndrome (HUS).

Methods

Two consecutive cases of hemolytic uremic syndrome were diagnosed in our service. In both patients the use of macrolides in patients taking Tacrolimus, resulted in high levels of Tacrolimus.

Results

The first patient was a 48 years old female with Bilateral emphysema. She underwent Single Sequential Lung Transplantation. She developed reperfusion injury requiring prolonged stay. Tacrolimus introduced (Day 51). The patient remained well up till 5 months later; Erythromycin commenced for chest infection. High Tacrolimus levels and a clinical diagnosis of HUS were made. She was treated with plasmapheresis successfully.

The second case was a 57 years old female with Emphysema & A1 Antithrypsin deficiency. She underwent Right Single Lung Transplantation. A2 rejection with mild Obliterative Bronchiolitis diagnosed 1 year later and she switched to Tacrolimus. She was admitted to her local Hospital two and a half years later with right middle lobe consolidation. The patient commenced on amoxicillin and clarithromycin. Worsening renal indices, high Tacrolimus levels, hemolytic anemia & low Platelets were detected. HUS diagnosed & treated with plasmapheresis.

Conclusions

There are 21 cases of HUS following lung transplantation in the literature that may have been induced by high tacrolimus levels. Macrolides in patients taking Cyclosporin or Tacrolimus lead to high levels. Mechanism of action could be glomeruloconstrictor effect with reduced GFR increased production of Endothelin-1 and increased Platelet aggregation.