Thrombotic microangiopathies

Vascular lesions of the pediatric orbit: A radiological walkthrough

Vascular anomalies of the pediatric orbit represent a heterogeneous group that include both vascular tumors and vascular malformations. The disorder may initially be silent and then associated with symptoms and/or function damage, depending on the type of vascular anomaly and its extension. Vascular tumors include benign, locally aggressive (or borderline) and malignant forms while vascular malformations are divided into "simple", "combined" and syndromic, or "low flow" or "high flow". Both entities can arise in isolation or as part of syndromes. In this review, we describe the imaging findings of the vascular lesions of the orbit in the pediatric population, which are key to obtain a correct diagnosis and to guide the appropriate treatment in the light of the new genetic and molecular discoveries, and the role of the radiologist in their multidisciplinary management. We will also touch upon the main syndromes associated with orbital vascular abnormalities.

Thrombotic microangiopathy in a very young infant with mitral valvuloplasty

BACKGROUND

Thrombotic microangiopathies (TMA) are microvascular occlusive disorders characterized by systemic or intrarenal platelet aggregation, thrombocytopenia, and red cell fragmentation. Post-operative TMA mostly occurs in adult patients with cardiovascular surgery, with the distinct pathophysiology from classical thrombotic thrombocytopenic purpura (TTP) although the exact pathophysiology remains unclear.

CASE PRESENTATION

A one-month-old infant developed TMA after the initial surgery of double outlet right ventricle. ADAM metallopeptidase with thrombospondin type 1 motif 13 (ADAMTS13) activity was sustained (64%) with the undetectable inhibitor. Von Willebrand factor (VWF) multimer analyses showed absent high-molecular weight multimers. Echocardiography disclosed severe mitral regurgitation. The mitral valve repair 32 days after the initial valvuloplasty led to prompt resolution of TMA. These suggested that TMA occurred in association with valvulopathy-triggered turbulent shear flow, mechanical hemolysis and endothelial damage. The consumption of large VWF multimers might account for the vascular high shear stress shown in Heyde syndrome.

CONCLUSION

The youngest case of post-operative TMA underscores the critical coagulopathy after the first surgical intervention for congenital heart disease.

A matched case-control study to assess the association between non-steroidal anti-inflammatory drug use and thrombotic microangiopathy

Several case reports suggest that non-steroidal anti-inflammatory drug (NSAID) use is associated with development of thrombotic microangiopathy (TMA). We conducted a matched population-based case-control study using linked administrative healthcare data in Ontario, Canada to assess the relationship between TMA hospitalization and recent exposure to prescription NSAIDs versus acetaminophen (acetaminophen was chosen as the referent drug because it has no known association with TMA). Cases and controls were drawn from a source population of adults who filled a prescription for either NSAIDs or acetaminophen between 1991 and 2015 (restricted to adults with prescription drug benefits [n = 3.6 million]). We identified 44 eligible cases with a hospital admission for incident TMA and a recent prescription for NSAIDs or acetaminophen. We successfully matched 38 cases (1:4) to 152 controls without TMA on demographics, risk factors for TMA, and indications for NSAID use. Cases and controls were similar with respect to age (71 years) and sex (63% women); however, on average, cases had more comorbidities than controls (12 vs. 14; p<0.05) and more primary care visits in the year before the index date (19 vs. 12; p<0.05). Cases were significantly less likely than controls to have received a recent prescription for NSAIDs (19/38 [50%] vs. 115/152 [76%], respectively; adjusted odds ratio 0.37, 95% confidence interval: 0.16 to 0.84). Results were similar in several sensitivity analyses. Overall, the results of this study do not support a harmful association between NSAID use and the development of TMA.

The role of von Willebrand factor in thrombotic microangiopathy

Thrombotic microangiopathy (TMA) is caused by thrombus formation in the microvasculature. The disease spectrum of TMA includes, amongst others, thrombotic thrombocytopenic purpura (TTP) and atypical haemolytic uraemic syndrome (aHUS). TTP is caused by defective cleavage of von Willebrand factor (VWF), whereas aHUS is caused by overshooting complement activation and subsequent endothelial cell (EC) injury. Despite their distinct pathophysiology, the clinical manifestation of TTP and aHUS consisting of microangiopathic haemolytic anaemia and thrombocytopenia is often similar and difficult to distinguish. Recent evidence hints at both a genetic and functional link between TTP and aHUS, especially between VWF and the complement system. There is novel in vitro evidence that complement activation not only results in VWF release from ECs, but that VWF also functions as a negative complement regulator, thus protecting the EC surface from ongoing complement attack. Although contrary to previous experimental work suggesting that complement can be activated on VWF multimers, there may be an explanation in vivo that rationalizes these apparently contradictory findings, whereby a system primarily meant to regulate becomes overwhelmed or pathologic in the disease state. The importance of unravelling these recent findings for our understanding of TMA pathology becomes even more evident considering that glomerular ECs express VWF in a heterogeneous pattern with an overall decreased expression level, thus potentially leaving the glomerular ECs vulnerable to complement-mediated injury. Taken together, these findings support the concept that TTP and aHUS represent two extreme ends of a TMA disease spectrum rather than isolated disease entities.

Scleroderma Renal Crisis: A Reversible Cause of Left Ventricular Dysfunction

We report a case of acute left ventricular dysfunction due to myocarditis, in the setting of a scleroderma renal crisis. The case is particularly intriguing for the favorable outcome of both symptoms and heart function following immunosuppressive therapy. We also highlight the changes observed over time with image techniques as well as in electrocardiograms.

Circulating IgM Requires Plasma Membrane Disruption to Bind Apoptotic and Non-Apoptotic Nucleated Cells and Erythrocytes

Autoimmunity is associated with defective phagocytic clearance of apoptotic cells. IgM deficient mice exhibit an autoimmune phenotype consistent with a role for circulating IgM antibodies in apoptotic cell clearance. We have extensively characterised IgM binding to non-apoptotic and apoptotic mouse thymocytes and human Jurkat cells using flow cytometry, confocal imaging and electron microscopy. We demonstrate strong specific IgM binding to a subset of Annexin-V (AnnV)+PI (Propidium Iodide)+ apoptotic cells with disrupted cell membranes. Electron microscopy studies indicated that IgM+AnnV+PI+ apoptotic cells exhibited morphologically advanced apoptosis with marked plasma membrane disruption compared to IgM-AnnV+PI+ apoptotic cells, suggesting that access to intracellular epitopes is required for IgM to bind. Strong and comparable binding of IgM to permeabilised non-apoptotic and apoptotic cells suggests that IgM bound epitopes are 'apoptosis independent' such that IgM may bind any cell with profound disruption of cell plasma membrane integrity. In addition, permeabilised erythrocytes exhibited significant IgM binding thus supporting the importance of cell membrane epitopes. These data suggest that IgM may recognize and tag damaged nucleated cells or erythrocytes that exhibit significant cell membrane disruption. The role of IgM in vivo in conditions characterized by severe cell damage such as ischemic injury, sepsis and thrombotic microangiopathies merits further exploration.

ADAMTS13 Endopeptidase Protects against Vascular Endothelial Growth Factor Inhibitor-Induced Thrombotic Microangiopathy

Thrombotic microangiopathy (TMA) is a life-threatening condition that affects some, but not all, recipients of vascular endothelial growth factor (VEGF) inhibitors given as part of chemotherapy. TMA is also a complication of preeclampsia, a disease characterized by excess production of the VEGF-scavenging soluble VEGF receptor 1 (soluble fms-like tyrosine kinase 1; sFlt-1). Risk factors for VEGF inhibitor-related TMA remain unknown. We hypothesized that deficiency of the VWF-cleaving ADAMTS13 endopeptidase contributes to the development of VEGF inhibitor-related TMA. ADAMTS13(-/-) mice overexpressing sFlt-1 presented all hallmarks of TMA, including thrombocytopenia, schistocytosis, anemia, and VWF-positive microthrombi in multiple organs. Similar to VEGF inhibitor-related TMA in humans, these mice exhibited severely impaired kidney function and hypertension. In contrast, wild-type mice overexpressing sFlt-1 developed modest hypertension but no other features of TMA. Recombinant ADAMTS13 therapy ameliorated all symptoms of TMA in ADAMTS13(-/-) mice overexpressing sFlt-1 and normalized BP in wild-type mice. ADAMTS13 activity may thus be a critical determinant for the development of TMA secondary to VEGF inhibition. Administration of recombinant ADAMTS13 may serve as a therapeutic approach to treat or prevent thrombotic complications of VEGF inhibition.

Deficiency in mouse hyaluronidase 2: a new mechanism of chronic thrombotic microangiopathy

Hyaluronan is a major component of the extracellular matrix and glycocalyx. Its main somatic degrading enzymes are hyaluronidases 1 and 2, neither of which is active in the bloodstream. We generated hyaluronidase 2-deficient mice. These animals suffer from chronic, mild anemia and thrombocytopenia, in parallel with a 10-fold increase in plasma hyaluronan concentration. In this study we explored the mechanism of these hematologic anomalies. The decreased erythrocyte and platelet counts were attributed to peripheral consumption. The erythrocyte half-life was reduced from 25 to 8 days without signs of premature aging. Hyaluronidase 2-deficient platelets were functional. Major intrinsic defects in erythrocyte membrane or stability, as well as detrimental effects of high hyaluronan levels on erythrocytes, were ruled out in vitro. Normal erythrocytes transfused into hyaluronidase 2-deficient mice were quickly destroyed but neither splenectomy nor anti-C5 administration prevented chronic hemolysis. Schistocytes were present in blood smears from hyaluronidase 2-deficient mice at a level of 1% to 6%, while virtually absent in control mice. Hyaluronidase 2-deficient mice had increased markers of endothelial damage and microvascular fibrin deposition, without renal failure, accumulation of ultra-large multimers of von Willebrand factor, deficiency of A Disintegrin And Metalloproteinase with ThromboSpondin type 1 motifs, member 13 (ADAMTS13), or hypertension. There was no sign of structural damage in hepatic or splenic sinusoids, or in any other microvessels. We conclude that hyaluronidase 2 deficiency induces chronic thrombotic microangiopathy with hemolytic anemia in mice. The link between this uncommon condition and hyaluronidase 2 remains to be explored in humans.

Plasma exchange induces vitamin D deficiency

BACKGROUND

Plasma exchange is used in the treatment of diseases mediated by pathogenic circulating proteins, or for transplant desensitization. Its non-targeted nature results in the depletion of physiologically important molecules, and it is often complicated by hypocalcaemia.

AIM

To determine the effects of plasma exchange on vitamin D binding protein (DBP) and associated vitamin D metabolites.

DESIGN

Single-centre prospective cohort study of 11 patients.

METHODS

DBP and vitamin D metabolites were measured before and immediately after five plasma exchanges, and 7 and 28 days after discontinuation of plasma exchange.

RESULTS

Plasma exchange reduced plasma DBP concentration from 196.9 ± 53.2 to 98.5 ± 34 μg/ml (P = 0.0001), 1,25-dihydroxyvitamin D from 103 ± 52 to 42 ± 4 pmol/l (P = 0.003) and 25-hydroxyvitamin D from 49.7 ± 29 to 22 ± 9.4 nmol/l (P = 0.0017), through their removal in effluent. After 7 days, DBP and 1,25-dihydroxyvitamin D were not significantly different from baseline, but 25-hydroxyvitamin D remained significantly lower after 7 days (26.4 ± 9.8 nmol/l, P = 0.02) and 28 days (30.8 ± 15.5 nmol/l, P = 0.048). Corrected calcium decreased from 2.23 ± 0.11 to 1.98 ± 0.08 mmol/l (P = 0.0007) immediately after five treatments. Plasma calcium was significantly associated with 1,25-dihydroxyvitamin D (r(2) = 0.79, P < 0.0001).

CONCLUSION

Plasma exchange induced an acute reversible decrease in plasma 1,25-dihydroxyvitamin D, DBP, calcium and a sustained decrease in plasma 25-hydroxyvitamin D.

Thrombotic microangiopathy in Interferon Beta treated multiple sclerosis patients: Review of literature and report of two new cases

Beta interferons (IFN-β) were the first approved disease modifying therapies (DMTs) for relapsing-remitting multiple sclerosis (RRMS) and are still the most-widely prescribed medications for this disease. Despite good overall long-term safety data with prolonged use of this group of drugs, they can rarely cause serious and sometimes life threatening adverse effects. In this article we report two cases of thrombotic microangiopathy occurring during prolonged use of IFN-β and review the available literature on this topic.

Thrombotic microangiopathy during docetaxel, trastuzumab, and carboplatin chemotherapy for early-stage HER2+ breast cancer: a case report

Chemotherapy-induced thrombotic microangiopathy is a severe illness that has occurred in a small number of patients treated with carboplatin and combination of docetaxel and trastuzumab chemotherapy. We describe herein the case of a patient with stage IIB breast cancer who developed thrombotic microangiopathy after five cycles of carboplatin, docetaxel, and trastuzumab.

Tacrolimus-associated thrombotic microangiopathy in a lung transplant recipient

A 25-year-old woman with a history of bilateral lung transplant secondary to cystic fibrosis presented with non-specific abdominal complaints and was found to have acute kidney injury, thrombocytopaenia and laboratory findings consistent with a microangiopathic haemolytic anaemia. Her thrombotic microangiopathy (TMA) was attributed to tacrolimus, which was discontinued and replaced with cyclosporine with resolution of her TMA and no subsequent complications. This is the fifth reported case of TMA associated with tacrolimus use in a lung transplant patient, and the third to be successfully managed with cyclosporine substitution. Clinicians must be aware of this uncommon, but likely under-reported complication of tacrolimus therapy in lung transplant recipients. Cyclosporine replacement may be used as a successful therapy to treat tacrolimus-associated TMA without increasing the risk of acute rejection that may be associated with other treatment strategies.

Acute Renal Failure due to Thrombotic Microangiopathy in Patient with Scleroderma: Autopsy Case Report

This study presents a patient who died of acute renal failure (ARF) as a complication of scleroderma. The patient remained normotensive throughout the clinical course. Myeloperoxidase-anti-neutrophil cytoplasmic antibody was negative. Autopsy revealed fibrin thrombi in the glomerular capillaries and afferent arterioles, mesangiolysis, and double contour of the glomerular basement membrane. Contrarily, "onionskin lesions" of renal interlobular arteries, the histological hallmark of scleroderma renal crisis, were not discovered. These findings suggested that thrombotic microangiopathy (TMA) was the cause of ARF. Although the frequency is not high, close monitoring should be given to TMA in scleroderma because of possible mortality.