Illustrated State-of-the-Art Capsules of the ISTH 2024 Congress.

Here, we present a series of illustrated capsules from the State of the Art (SOA) speakers at the 2024 International Society on Thrombosis and Haemostasis Congress in Bangkok, Thailand. This year's Congress marks the first time that the International Society on Thrombosis and Haemostasis has held its flagship scientific meeting in Southeast Asia and is the first to be organized by an international Planning Committee. The Bangkok program will feature innovative science and clinical updates from around the world, reflecting the diversity and multidisciplinary growth of our field. In these illustrated SOA capsules, you will find an exploration of novel models of thrombosis and bleeding and biomaterial discoveries that can trigger or block coagulation. Thromboinflammation is now understood to drive many disease states, and the SOA speakers cover cellular and coagulation responses to COVID-19 and other infections. The theme of crosstalk between coagulation and inflammation expands with capsules on protein S signaling, complement, and fibrinolytic inhibitors. Novel agents for hemophilia and thrombosis prevention are introduced. Challenging clinical conditions are also covered, such as inherited platelet disorders and antiphospholipid antibody syndrome. The scientific program in Bangkok will also showcase the work of clinicians and scientists from all parts of the world and chronicle real-world challenges. For example, 2 SOA capsules address the diagnosis and management of von Willebrand disease in low-income settings. Take some time to browse through these short illustrated reviews; we're sure that you'll be entertained, educated, and inspired to further explore the world of thrombosis and hemostasis.

Long-term outcomes of pulmonary embolism in children and adolescents.

ABSTRACT: Knowledge regarding the long-term consequences of pulmonary embolism (PE) in children is limited. This cohort study describes the long-term outcomes of PE in children who were followed-up at a single-center institution using a local protocol that included clinical evaluation, chest imaging, echocardiography, pulmonary function tests, and cardiopulmonary exercise tests at follow-up, starting 3 to 6 months after acute PE. Children objectively diagnosed with PE at age 0 to 18 years, who had ≥6 months of follow-up were included. Study outcomes consisted of PE resolution, PE recurrence, death, and functional outcomes (dyspnea, impaired pulmonary or cardiac function, impaired aerobic capacity, and post-PE syndrome). The frequency of outcomes was compared between patients with/without underlying conditions. In total, 150 patients were included; median age at PE was 16 years (25th-75th percentile, 14-17 years); 61% had underlying conditions. PE did not resolve in 29%, recurrence happened in 9%, and death in 5%. One-third of patients had at least 1 documented abnormal functional finding at follow-up (ventilatory impairments, 31%; impaired aerobic capacity, 31%; dyspnea, 26%; and abnormal diffusing capacity of the lungs to carbon monoxide, 22%). Most abnormalities were transient. When alternative explanations for the impairments were considered, the frequency of post-PE syndrome was lower, ranging between 0.7% and 8.5%. Patients with underlying conditions had significantly higher recurrence, more pulmonary function and ventilatory impairments, and poorer exercise capacity. Exercise intolerance was, in turn, most frequently because of deconditioning than to respiratory or cardiac limitation, highlighting the importance of physical activity promotion in children with PE.

Between Scylla and Charybdis: thrombosis in children with hemophilia.

Thromboembolism is an infrequent complication in children with hemophilia that has been traditionally associated with the presence of a central venous access device. Novel rebalancing agents have shown promising results as prophylactic therapies to minimize the risk of bleeding but both thromboembolism and thrombotic microangiopathy have been reported as complications. The management of thrombosis in children with hemophilia is particularly challenging given the inherent risk of bleeding. In this paper, we present clinical vignettes to review the literature, highlight challenges, and describe our approach to managing thromboembolism in children with hemophilia.

Thiopurine Methyltransferase Intermediate Metabolizer Status and Thiopurine-Associated Toxicity During Maintenance Therapy in Childhood Acute Lymphoblastic Leukemia.

Mercaptopurine is a cornerstone of maintenance chemotherapy in childhood acute lymphoblastic leukemia (ALL). Its cytotoxic effects are mediated by 6-thioguanine nucleotides (TGNs) incorporation into lymphocyte DNA. Thiopurine methyltransferase (TPMT) inactivates mercaptopurine, and deficiency resulting from genetic variants increases TGN exposure and hematopoietic toxicity. Although mercaptopurine-dose reduction reduces toxicity risk without compromising relapse rate in patients with TPMT deficiency, dosing recommendations for those with moderately reduced activity (intermediate metabolizer (IM)) are less clear and their clinical impacts have yet to be established. This cohort study assessed the effect of TPMT IM status on mercaptopurine-associated toxicity and TGN blood exposure in pediatric patients with ALL initiated on standard dose mercaptopurine. Of 88 patients studied (mean age 4.8 years), 10 (11.4%) were TPMT IM, and all had undergone ≥ 3 cycles of maintenance therapy (80% completed). A larger proportion of TPMT IM than normal metabolizers (NM) had febrile neutropenia (FN) during the first two cycles of maintenance, reaching significance in the second cycle (57% vs. 15%, respectively; odds ratio = 7.33, P < 0.05). Compared to NM, FN events occurred more frequently and with prolonged duration in IM in cycles 1 and 2 (adjusted P < 0.05). IM had a 2.46-fold increased hazard ratio for FN, and about twofold higher TGN level than NM (P < 0.05). Myelotoxicity was more common in IM than NM (86% vs. 42%, respectively) during cycle 2 (odds ratio = 8.2, P < 0.05). TPMT IM initiated at a standard mercaptopurine dose are at greater risk for FN during early cycles of maintenance therapy, thus our findings support genotype-guided dose adjustment to reduce toxicity.

Osteosarcoma emboli presenting as chronic thromboembolic pulmonary hypertension in a child.

A 13-year-old girl presented with hypoxemia during adjuvant chemotherapy for an osteosarcoma of the left distal femur. She underwent an amputation complicated by a post-operative pulmonary embolism (PE). Three months post-operatively, she was admitted to hospital with severe hypoxemia and diagnosed with pulmonary hypertension on echocardiogram in the context of extensive bilateral PE on computed tomography. She was planned for elective pulmonary thromboendarterectomy, but rapidly deteriorated requiring emergent surgery. At the time of surgery, she was found to have extensive tumor emboli throughout both pulmonary arteries. She recovered well post-operatively but died 2 months later from progressive disease.

Reassessing the Need for Preoperative Transfusions in Sickle Cell Disease Patients With an Elevated Baseline Hemoglobin-A Retrospective Study.

BACKGROUND: Current guidelines recommend a preoperative hemoglobin of 10.0 g/dL in patients with sickle cell disease [SCD], however, this threshold continues to be an area of controversy. Previous studies demonstrating the benefits of preoperative transfusions have largely not captured patients with elevated baseline hemoglobin, in part due to low hydroxyurea uptake and exclusion of nonhemoglobin SS SCD. MATERIALS AND METHODS: We conducted a retrospective chart review of patients with SCD <18 years of age undergoing low and medium-risk procedures at 2 academic medical centers in Canada between 2007 and 2017. The primary objective was to study the association of preoperative transfusion on postoperative complications in patients with SCD with baseline hemoglobin between 9.0 and 10.0 g/dL. Multivariable logistic regression was used to estimate the adjusted effect of preoperative transfusion on the risk of developing postoperative complications. RESULTS: In all, 159 procedures in patients with hemoglobin <9.0 g/dL [Hb <9.0 ] and 173 procedures in patients with hemoglobin between 9.0 and 10.0 g/dL [Hb 9.0-10.0 ] were analyzed. In the absence of preoperative transfusion, Hb 9.0-10.0 patients had lower overall complications [23% vs. 34%] compared with Hb <9.0 patients [OR 0.29, 95% CI 0.12-0.72, P =0.008]. In total, 75% of Hb <9.0 and 21% of Hb 9.0-10.0 patients received a preoperative simple transfusion. Transfusion was associated with increased risk of postoperative complications in Hb 9.0-10.0 [OR 3.02, 95% CI 1.26-7.23, P =0.013], but not Hb <9.0 patients [OR 0.64, 95% CI 0.28-1.45, P =0.30]. CONCLUSIONS: Simple transfusion may not be warranted in Hb 9.0-10.0 patients undergoing low-risk procedures. Prospective studies validating these findings are needed.

Poor outcome after hematopoietic stem cell transplantation of patients with unclassified inherited bone marrow failure syndromes.

Classification of inherited bone marrow failure syndromes (IBMFSs) according to clinical and genetic diagnoses enables proper adjustment of treatment. Unfortunately, 30% of patients enrolled in the Canadian Inherited Marrow Failure Registry (CIMFR) with features suggesting hereditability could not be classified with a specific syndromic diagnosis. We analyzed the outcome of hematopoietic stem cell transplantation (HSCT) in unclassified IBMFSs (uIBMFSs) and the factors associated with outcome. Twenty-two patients with uIBMFSs and 70 patients with classified IBMFSs underwent HSCT. Five-year overall survival of uIBMFS patients after HSCT was inferior to that of patients with classified IBMFSs (56% vs 76.5%). The outcome of patients with uIBMFS who received cord blood was significantly lower than that of patients who received other stem cell sources (14.8% vs 90.9%). Engraftment failure was higher among patients with uIBMFS who received cord blood than those who received bone marrow. None of the following factors were significantly associated with poor survival: transfusion load, transplant indication, the intensity of conditioning regimen, human leukocyte antigen-identical sibling/alternative donor. We suggest that identifying the genetic diagnosis is essential to modulate the transplant procedure including conditioning agents and stem cell sources for better outcome and the standard cord blood transplantation (CBT) should be avoided in uIBMFS.

The use of rapamycin to treat vascular tumours and malformations: A single-centre experience.

OBJECTIVES: To assess the safety and efficacy of rapamycin in treating children with vascular tumours and malformations. STUDY DESIGN: We performed a retrospective review at a large tertiary care paediatric centre to assess the efficacy and safety of using rapamycin to treat vascular tumours and malformations. Response to therapy was defined by patient-reported symptom improvement, radiological reduction in size of lesions, and/or improvement of laboratory parameters. RESULTS: Forty-two patients (7 with vascular tumours and 35 with vascular malformations) have been treated with rapamycin. Despite 33 of 42 patients being diagnosed in the first year of life, the median age of initiating rapamycin was 11 years. Of the 38 children treated for a minimum of 4 months, 29 (76%) exhibited a clinical response. Twenty-one patients had follow-up imaging studies and of these, 16 (76%) had radiographic decrease in lesion size. Median time to demonstration of response was 49 days. All five children with vascular tumours and all three children with vascular malformations under the age of 4 years showed a clinical response. Response rate was lower for children ≥ 4 years of age (0/2, 0% for vascular tumours; 21/28, 75% for vascular malformations). No patient experienced an infection directly related to rapamycin or discontinued rapamycin due to toxicity. CONCLUSIONS: Rapamycin is safe and efficacious in most children with select vascular tumours and malformations. Young children appear to respond better, suggesting that early initiation of rapamycin should be considered.

Renal Infarcts-A Perplexing Case in the Middle of the COVID-19 Pandemic.

Renal infarction is a rare finding in children. Associations between SARS-CoV-2 infections and thromboembolic events including renal infarcts have been described in adults. Although a similar association in children has not yet been described with this pandemic, the pediatric literature is still evolving with the recognition of new manifestations including the post-infectious Multisystem Inflammatory Syndrome in Children (MIS-C). We report the rare event of multiple renal infarcts in a 6-year-old boy manifesting several features of MIS-C 9 weeks following a self-limiting febrile illness characteristic of COVID-19. An underlying Factor V Leiden mutation was identified in this child but felt to be insufficient on its own to explain his clinical presentation. As SARS-CoV-2 testing was delayed, the failure to identify viral RNA or antibodies may not exclude the virus' potential role in precipitating the infarct in this host. Given that renal infarcts have been described in adult patients with COVID-19, reporting this perplexing case where SARS-CoV-2 may have played a role, may help identify this potential complication.

Genotype-phenotype correlation in children with hereditary spherocytosis.

Hereditary spherocytosis (HS) is a common inherited haemolytic anaemia attributed to disturbances in five different red cell membrane proteins. We performed a retrospective study of 166 children with HS and describe the clinical phenotype according to the genotype. In 160/166 (97%) children with HS a disease-causing mutation was identified. Pathogenic variants in ANK1, SPTB, SLC4A1 and SPTA1 were found in 49%, 33%, 13% and 5% of patients. Children with SLC4A1-HS had the mildest phenotype, showing the highest haemoglobin (P < 0·001), lowest reticulocyte counts (P < 0·001) and lowest unconjugated bilirubin levels (P = 0·006), and none required splenectomy in childhood (P < 0·001). Conversely, children with autosomal recessive SPTA1-HS had the most severe clinical phenotype, with almost all patients undergoing splenectomy in early childhood. Patients with ANK1 and SPTB variants showed a similar clinical phenotype. Within each gene, variant type or location did not predict disease severity or likelihood of splenectomy. Among patients with a genetic diagnosis, 47 (29%) underwent splenectomy (23 partial; 24 total) while 57 (36%) underwent cholecystectomy. Total splenectomy led to greater improvements in haemoglobin (P = 0·02). Select use of genetic testing (especially in patients without a family history) may help predict clinical phenotype in childhood and guide family counselling.

Abnormal hemostasis in children with vascular anomalies, part I: Thrombocytopenias among different vascular anomalies.

Long before the classification of vascular anomalies from the International Society for the Study of Vascular Anomalies (ISSVA) provided a framework to differentiate vascular anomalies, otherwise known as vascular birthmarks, it was recognized that patients with such lesions can present with acute life-threatening hemostatic and/or thrombotic complications, as well as chronic long-standing bleeding or thrombotic issues. Scenarios such as a rapidly growing vascular lesion with severe acute thrombocytopenia, a visceral hemorrhagic lesion, a lesion associated with repetitive and painful superficial thrombosis, and cases of unprovoked or post-procedural fatal pulmonary embolism highlight the wide spectrum of manifestations of abnormal coagulation in patients with vascular anomalies. The separation of vascular anomalies into two distinct groups, vascular tumors and vascular malformations, was followed by the characterization that their respective coagulopathies were due to either a derangement of platelets or to a disequilibrium of the patient's coagulation/fibrinolytic process. This configuration of coagulopathies will be the foundation for this two-chapter review series. In the initial review, coagulopathies where thrombocytopenia is the main feature will be characterized, whereas the second review will focus on vascular malformations that have a coagulation disorder secondary to some degree of coagulation consumption and/or fibrinolytic pathway derangement.

Effectiveness and Safety of Primary Thromboprophylaxis in Children with Cancer: A Systematic Review of the Literature and Network Meta-Analysis.

Thromboembolism (TE) is a well-recognized complication of pediatric cancer and can lead to mortality and excess morbidity. There is conflicting evidence about the effectiveness and safety of thromboprophylaxis in children. We conducted a systematic literature review and network meta-analysis of primary pharmacological thromboprophylaxis in children and adolescents (0-21 years) with cancer. The primary outcomes were objectively proven TE and major bleeding. The network meta-analysis included comparisons of multiple alternatives simultaneously: antithrombin (AT) replacement, low molecular weight heparin (LMWH), vitamin K antagonists (VKAs), and standard of care (SOC) defined as no thromboprophylaxis or low-dose heparin for catheter patency. Six articles describing 1,318 patients were included (mean age: 6.7 years, 56.7% male). Acute lymphoblastic leukemia was the underlying diagnosis in 97.5% of patients. All studies were considered at moderate or high risk of bias. LMWH was the only agent associated with lower odds of TE compared with SOC (odds ratio [OR]: 0.23, 95% confidence interval [CI]: 0.06-0.81). No statistically significant difference was detected between other thromboprophylaxis modalities and SOC. Tau2 and I 2 suggested a high degree of heterogeneity. No statistically significant differences in the odds of major bleeding were found between AT replacement, LMWH, VKA, and SOC. Current evidence suggests that low-dose LMWH is effective and safe to prevent TE in children with cancer but is insufficient to conclude if AT replacement or VKA are effective thromboprophylaxis options. Further research, notably randomized controlled trials enrolling children with diverse types of cancer, is crucially needed.

Mild Hereditary Spherocytosis without Accompanying Hereditary Haemochromatosis: An Unrecognised Cause of Iron Overload.

Hereditary spherocytosis (HS) is a common inherited haemolytic anaemia and has great variability in its presentation. Non-transfusion iron overload in HS has only been reported with co-inheritance of hereditary haemochromatosis (HHC). We present 4 unrelated patients of East Asian ethnicity with mild HS and significant non-transfusion iron overload in the absence of known disease-causing mutations in HHC genes. We hypothesise that, in patients with mild HS, life-long chronic haemolysis and erythropoietic drive may promote iron absorption. This suggests that mild HS may not be entirely benign, and that patients with mild HS should be monitored for iron overload.

The risk of traumatic lumbar punctures in children with acute lymphoblastic leukaemia.

BACKGROUND: Traumatic lumbar punctures with blasts (TLP+) in children with acute lymphoblastic leukaemia (ALL) obscure central nervous system status and are associated with a poorer event-free survival (EFS). METHODS: We conducted a retrospective cohort study of all lumbar punctures (LPs) for children with ALL diagnosed at our institution from 2005 to 2009. We utilised random-effects and fixed-effects repeated-measures logistic regression analyses to identify risk factors for TLPs. Fixed-effects models use each patient as his or her own control. We used survival analysis to describe outcomes after a TLP+. RESULTS: 264 children underwent 5267 evaluable lumbar punctures (LPs), of which 944 (17.9%) were traumatic. In the multivariable random-effects model, variables significantly associated with TLPs were age <1year (odds ratio (OR) 3.46, 95% confidence interval (CI) 2.06-5.81) or age ⩾10years (OR 2.00, CI 1.66-2.40); body mass index percentile ⩾95 (OR 1.44, CI 1.19-1.75); platelet count <100×10(3)/µL (OR 1.49, CI 1.08-20.7); fewer days since previous LP (OR 5.13, CI 2.34-11.25 for ⩾16days versus 0-3days); and a preceding TLP (OR 1.43, CI 1.19-1.73). In the fixed-effects model, image-guidance reduced the odds of TLP (OR 0.55, CI 0.32-0.95). The 5-year EFS (±SE) for children with TLP+ (77±8%) was significantly lower than for children with CNS1 status (93±2%; p=0.002). CONCLUSIONS: The frequency of TLP remains high. Consistent with previous studies, a TLP+ at diagnosis was associated with a poorer EFS. These risk factors can allow identifying interventions to reduce TLPs and directing interventions to those at highest risk.