Optimizing dynamic predictions from joint models using super learning.

Joint models for longitudinal and time-to-event data are often employed to calculate dynamic individualized predictions used in numerous applications of precision medicine. Two components of joint models that influence the accuracy of these predictions are the shape of the longitudinal trajectories and the functional form linking the longitudinal outcome history to the hazard of the event. Finding a single well-specified model that produces accurate predictions for all subjects and follow-up times can be challenging, especially when considering multiple longitudinal outcomes. In this work, we use the concept of super learning and avoid selecting a single model. In particular, we specify a weighted combination of the dynamic predictions calculated from a library of joint models with different specifications. The weights are selected to optimize a predictive accuracy metric using V-fold cross-validation. We use as predictive accuracy measures the expected quadratic prediction error and the expected predictive cross-entropy. In a simulation study, we found that the super learning approach produces results very similar to the Oracle model, which was the model with the best performance in the test datasets. All proposed methodology is implemented in the freely available R package JMbayes2.

Establishing how much improvement in lung function and distance walked is clinically important for adult patients with Pompe disease.

BACKGROUND AND PURPOSE: Pompe disease is a rare, inheritable, progressive metabolic myopathy. This study aimed to estimate the minimal clinically important difference (MCID) for an improvement in forced vital capacity in the upright seated position (FVCup) and the 6-min walk test (6MWT) after a year of treatment with enzyme replacement therapy. METHODS: Data were obtained from two prospective follow-up studies. Between-group and within-group MCIDs were estimated using anchor-based methods. Additionally, a distribution-based method was used to generate supportive evidence. As anchors, self-reported change in health and in physical functioning, shortness of breath and a categorization of the Short-Form 36 Physical Component Summary score were used. Anchor appropriateness was assessed using Spearman correlations (absolute values ≥0.29) and a sufficient number of observations in each category. RESULTS: In all, 102 patients had at least one FVCup or 6MWT measurement during enzyme replacement therapy. Based on the anchors assessed as appropriate, the between-group MCID for an improvement in FVCup ranged from 2.47% to 4.83% points. For the 6MWT, it ranged from 0.35% to 7.47% points which is equivalent to a distance of 2.18-46.61 m and 1.97-42.13 m for, respectively, a man and a woman of age 50, height 1.75 m and weight 80 kg. The results of the distribution-based method were within these ranges when applied to change in the outcome values. CONCLUSION: The MCIDs for FVCup and 6MWT derived in this study can be used to interpret differences between and within groups of patients with Pompe disease in clinical trials and cohort studies.

Regional aortic wall shear stress increases over time in patients with a bicuspid aortic valve.

BACKGROUND: Aortic wall shear stress (WSS) is a known predictor of ascending aortic growth in patients with a bicuspid aortic valve (BAV). The aim of this study was to study regional WSS and changes over time in BAV patients. METHODS: BAV patients and age-matched healthy controls underwent four-dimensional (4D) flow cardiovascular magnetic resonance (CMR). Regional, peak systolic ascending aortic WSS, aortic valve function, aortic stiffness measures, and aortic dimensions were assessed. In BAV patients, 4D flow CMR was repeated after 3 years of follow-up and both at baseline and follow-up computed tomography angiography (CTA) were acquired. Aortic growth (volume increase of ≥5%) was measured on CTA. Regional WSS differences within patients' aorta and WSS changes over time were analyzed using linear mixed-effect models and were associated with clinical parameters. RESULTS: Thirty BAV patients (aged 34 years [interquartile range (IQR) 25-41]) were included in the follow-up analysis. Additionally, another 16 BAV patients and 32 healthy controls (aged 33 years [IQR 28-48]) were included for other regional analyses. Magnitude, axial, and circumferential WSS increased over time (all p < 0.001) irrespective of aortic growth. The percentage of regions exposed to a magnitude WSS >95th percentile of healthy controls increased from 21% (baseline 506/2400 regions) to 31% (follow-up 734/2400 regions) (p < 0.001). WSS angle, a measure of helicity near the aortic wall, decreased during follow-up. Magnitude WSS changes over time were associated with systolic blood pressure, peak aortic valve velocity, aortic valve regurgitation fraction, aortic stiffness indexes, and normalized flow displacement (all p < 0.05). CONCLUSION: An increase in regional WSS over time was observed in BAV patients, irrespective of aortic growth. The increasing WSSs, comprising a larger area of the aorta, warrant further research to investigate the possible predictive value for aortic dissection.

Biomarkers predicting the effect of anti-TNF treatment in paediatric and adult inflammatory bowel disease.

OBJECTIVES: Paediatric and adult inflammatory bowel disease (pIBD, aIBD) patients may lose response to anti-tumour necrosis factor (TNF) treatment within the first year. Adult-extrapolated weight-based dosing is incorrect in children, due to age-related pharmacokinetic differences. We investigated biomarkers for initial and maintenance of response to infliximab (IFX) or adalimumab (ADA), comparing pIBD and aIBD patients. METHODS: In this prospective, observational study, pIBD (n = 24) and aIBD (n = 21) patients were included when initiating anti-TNF. Escalation from standard dosing and continued anti-TNF at 12 and 18 months were assessed. Biomarkers included clinical laboratory parameters, faecal calprotectin (FCP) and IFX trough levels (TLs). Plasma proteomics was performed in pIBD. RESULTS: During our study, treatment escalation (in clinical loss of response) occurred more common in pIBD versus aIBD (p = 0.02). We established that IFX therapy escalation in pIBD patients was not due to low infliximab levels. We identified 9 pro-inflammatory proteins that were elevated in patients losing response. CONCLUSION: Anti-TNF exposure-response relationship may be different in pIBD versus aIBD. No biomarkers for maintained response were identified, but 9 inflammatory proteins were of interest as potential predictors for loss of response in pIBD.

An illness-death multistate model to implement delta adjustment and reference-based imputation with time-to-event endpoints.

With a treatment policy strategy, therapies are evaluated regardless of the disturbance caused by intercurrent events (ICEs). Implementing this estimand is challenging if subjects are not followed up after the ICE. This circumstance can be dealt with using delta adjustment (DA) or reference-based (RB) imputation. In the survival field, DA and RB imputation have been researched so far using multiple imputation (MI). Here, we present a fully analytical solution. We use the illness-death multistate model with the following transitions: (a) from the initial state to the event of interest, (b) from the initial state to the ICE, and (c) from the ICE to the event. We estimate the intensity function of transitions (a) and (b) using flexible parametric survival models. Transition (c) is assumed unobserved but identifiable using DA or RB imputation assumptions. Various rules have been considered: no ICE effect, DA under proportional hazards (PH) or additive hazards (AH), jump to reference (J2R), and (either PH or AH) copy increment from reference. We obtain the marginal survival curve of interest by calculating, via numerical integration, the probability of transitioning from the initial state to the event of interest regardless of having passed or not by the ICE state. We use the delta method to obtain standard errors (SEs). Finally, we quantify the performance of the proposed estimator through simulations and compare it against MI. Our analytical solution is more efficient than MI and avoids SE misestimation-a known phenomenon associated with Rubin's variance equation.

Association between changes in pulmonary function and in patient reported outcomes during enzyme therapy of adult patients with late-onset Pompe disease.

Pompe disease is a rare, progressive, and metabolic myopathy. Reduced pulmonary function is one of the main problems seen in adult patients with late-onset Pompe disease (LOPD). We aimed to explore the association between changes over time in pulmonary function and in patient-reported outcome measures (PROMs), in these patients treated with enzyme replacement therapy (ERT). This is a post hoc analysis of two cohort studies. Pulmonary function was assessed as forced vital capacity in the upright position (FVCup ). As PROMs, we assessed the physical component summary score (PCS) of the Medical Outcome Study 36-item Short-Form Health Survey (SF-36) and daily life activities (Rasch-Built Pompe-Specific Activity [R-PACT] scale). We fitted Bayesian multivariate mixed-effects models. In the models of PROMs, we assumed a linear association with FVCup , and adjusted for time (nonlinear), sex, and age and disease duration at the start of ERT. One hundred and one patients were eligible for analysis. PCS and R-PAct were positively associated with FVCup , while their relation with time was nonlinear (initial increase then decrease). A 1%-point increase in FVCup is expected to increase PCS by 0.14 points (95% Credible Interval: [0.09;0.19]) and R-PACT by 0.41 points [0.33;0.49] at the same time point. In the first year of ERT, we expect a change of PCS and R-PAct scores by +0.42 and +0.80 points, and in the 5th year of +0.16 and +0.45, respectively. We conclude that the physical domain of quality of life and daily life activities improve when FVCup increases during ERT.

Validation and Reference Scores of the Transition Readiness Assessment Questionnaire in Adolescent and Young Adult IBD Patients.

OBJECTIVES: Transition readiness can predict a successful transition from pediatric to adult care. This study aimed to validate and develop age-dependent reference scores for the (Dutch version of) Transition Readiness Assessment Questionnaire (TRAQ), in adolescents and young adults (AYAs) with inflammatory bowel disease (IBD). METHODS: TRAQ has 20 items (score 1-5) distributed over 5 domains (total sum score 100) and is completed by AYAs. Following the COnsensus-based Standards for the selection of health Measurement INstruments methodology, we conducted the translation, back-to back translation, pretesting, and validation of the final Dutch version of TRAQ (TRAQ-NL) questionnaire. We used a Rasch model for structural validation, hypothesis testing for construct validity, and Cronbach alpha to demonstrate reliability. Reference scores were calculated using percentiles. RESULTS: Two hundred fifty TRAQ questionnaires were evaluated in 136 AYAs with IBD [56% Crohn disease, 58% male, median age 17.5 years (range 15.7-20.4)]. The overall mean item score was 3.87 (range 1.45-5). With good reliability (Cronbach alpha 0.87), TRAQ-NL discriminated well between knowledge levels, especially in the lower levels. Transition readiness was defined as low, moderate, adequate, or excellent in patients with TRAQ percentile scores (PC) <25th (<3.375 mean item score), 25th-50th (3.375-3.9), 50th-90th (3.91-4.7), or >90th (>4.7). Younger patients, concomitant illness, fewer visits to the transition clinic, and parental dependence were associated with significantly lower TRAQ scores. CONCLUSION: TRAQ(-NL) is reliable and valid, with age-dependent PC to identify (in)adequate transfer readiness. TRAQ can now be more easily used as a patient-reported outcome measure to monitor transition readiness longitudinally in routine care for AYAs IBD patients.

Gastrointestinal Biomarkers and Their Association with Feeding in the First Five Days of Pediatric Critical Illness.

OBJECTIVES: Predicting the patients' tolerance to enteral nutrition (EN) would help clinicians optimize individual nutritional intake. This study investigated the course of several gastrointestinal (GI) biomarkers and their association with EN advancement (ENA) longitudinally during pediatric intensive care unit (PICU) admission. METHODS: This is a secondary analysis of the Early versus Late Parenteral Nutrition in the Pediatric Intensive Care Unit randomized controlled trial. EN was started early and increased gradually. The cholecystokinin (CCK), leptin, glucagon, intestinal fatty acid-binding protein 2 (I-FABP2), and citrulline plasma concentrations were measured upon PICU admission, day 3 and day 5. ENA was defined as kcal EN provided as % of predicted resting energy expenditure. The course of the biomarkers and ENA was examined in patients with samples on all time points using Friedman and Wilcoxon signed-rank tests. The association of ENA with the biomarkers was examined using a 2-part mixed-effects model with data of the complete population, adjusted for possible confounders. RESULTS: For 172 patients, median age 8.6 years (first quartile; third quartile: 4.2; 13.4), samples were available, of which 55 had samples on all time points. The median ENA was 0 (0; 0) on admission, 14.5 (0.0; 43.8) on day 3, and 28.0 (7.6; 94.8) on day 5. During PICU stay, CCK and I-FABP2 concentrations decreased significantly, whereas glucagon concentrations increased significantly, and leptin and citrulline remained stable. None of the biomarkers was longitudinally associated with ENA. CONCLUSIONS: Based on the current evidence, CCK, leptin, glucagon, I-FABP2, and citrulline appear to have no added value in predicting ENA in the first 5 days of pediatric critical illness.

Clinical consequences of nonadherence to Barrett's esophagus surveillance recommendations: a Multicenter prospective cohort study.

Half of Barrett's esophagus (BE) surveillance endoscopies do not adhere to guideline recommendations. In this multicenter prospective cohort study, we assessed the clinical consequences of nonadherence to recommended surveillance intervals and biopsy protocol. Data from BE surveillance patients were collected from endoscopy and pathology reports; questionnaires were distributed among endoscopists. We estimated the association between (non)adherence and (i) endoscopic curability of esophageal adenocarcinoma (EAC), (ii) mortality, and (iii) misclassification of histological diagnosis according to a multistate hidden Markov model. Potential explanatory parameters (patient, facility, endoscopist variables) for nonadherence, related to clinical impact, were analyzed. In 726 BE patients, 3802 endoscopies were performed by 167 endoscopists. Adherence to surveillance interval was 16% for non-dysplastic (ND)BE, 55% for low-grade dysplasia (LGD), and 54% of endoscopies followed the Seattle protocol. There was no evidence to support the following statements: longer surveillance intervals or fewer biopsies than recommended affect endoscopic curability of EAC or cause-specific mortality (P > 0.20); insufficient biopsies affect the probability of NDBE (OR 1.0) or LGD (OR 2.3) being misclassified as high-grade dysplasia/EAC (P > 0.05). Better adherence was associated with older patients (OR 1.1), BE segments ≤ 2 cm (OR 8.3), visible abnormalities (OR 1.8, all P ≤ 0.05), endoscopists with a subspecialty (OR 3.2), and endoscopists who deemed histological diagnosis an adequate marker (OR 2.0). Clinical consequences of nonadherence to guidelines appeared to be limited with respect to endoscopic curability of EAC and mortality. This indicates that BE surveillance recommendations should be optimized to minimize the burden of endoscopies.

First-line treatment with infliximab versus conventional treatment in children with newly diagnosed moderate-to-severe Crohn's disease: an open-label multicentre randomised controlled trial.

OBJECTIVE: In newly diagnosed paediatric patients with moderate-to-severe Crohn's disease (CD), infliximab (IFX) is initiated once exclusive enteral nutrition (EEN), corticosteroid and immunomodulator therapies have failed. We aimed to investigate whether starting first-line IFX (FL-IFX) is more effective to achieve and maintain remission than conventional treatment. DESIGN: In this multicentre open-label randomised controlled trial, untreated patients with a new diagnosis of CD (3-17 years old, weighted Paediatric CD Activity Index score (wPCDAI) >40) were assigned to groups that received five infusions of 5 mg/kg IFX at weeks 0, 2, 6, 14 and 22 (FL-IFX), or EEN or oral prednisolone (1 mg/kg, maximum 40 mg) (conventional). The primary outcome was clinical remission on azathioprine, defined as a wPCDAI <12.5 at week 52, without need for treatment escalation, using intention-to-treat analysis. RESULTS: 100 patients were included, 50 in the FL-IFX group and 50 in the conventional group. Four patients did not receive treatment as per protocol. At week 10, a higher proportion of patients in the FL-IFX group than in the conventional group achieved clinical (59% vs 34%, respectively, p=0.021) and endoscopic remission (59% vs 17%, respectively, p=0.001). At week 52, the proportion of patients in clinical remission was not significantly different (p=0.421). However, 19/46 (41%) patients in the FL-IFX group were in clinical remission on azathioprine monotherapy without need for treatment escalation vs 7/48 (15%) in the conventional group (p=0.004). CONCLUSIONS: FL-IFX was superior to conventional treatment in achieving short-term clinical and endoscopic remission, and had greater likelihood of maintaining clinical remission at week 52 on azathioprine monotherapy. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Registry (NCT02517684).

Long-term Follow-up of a Randomized Clinical Trial Comparing Endovascular Revascularization Plus Supervised Exercise With Supervised Exercise Only for Intermittent Claudication.

OBJECTIVE: The goal of this study was to assess the long-term effectiveness of combination therapy for intermittent claudication, compared with supervised exercise only. BACKGROUND: Supervised exercise therapy is recommended as first-line treatment for intermittent claudication by recent guidelines. Combining endovascular revascularization plus supervised exercise shows promising results; however, there is a lack of long-term follow-up. METHODS: The ERASE study is a multicenter randomized clinical trial, including patients between May 2010 and February 2013 with intermittent claudication. Interventions were combination of endovascular revascularization plus supervised exercise (n = 106) or supervised exercise only (n = 106). Primary endpoint was the difference in maximum walking distance at long-term follow-up. Secondary endpoints included differences in pain-free walking distance, ankle-brachial index, quality of life, progression to critical limb ischemia, and revascularization procedures during follow-up. This randomized trial report is based on a post hoc analysis of extended follow-up beyond that of the initial trial. Patients were followed up until 31 July 2017. Data were analyzed according to the intention-to-treat principle. RESULTS: Median long-term follow-up was 5.4 years (IQR 4.9-5.7). Treadmill test was completed for 128/212 (60%) patients. Whereas the difference in maximum walking distance significantly favored combination therapy at 1-year follow-up, the difference at 5-year follow-up was no longer significant (53 m; 99% CI-225 to 331; P = 0.62). No difference in pain-free walking distance, ankle-brachial index, and quality of life was found during long-term follow-up. We found that supervised exercise was associated with an increased hazard of a revascularization procedure during follow-up (HR 2.50; 99% CI 1.27-4.90; P < 0.001). The total number of revascularization procedures (including randomized treatment) was lower in the exercise only group compared to that in the combination therapy group (65 vs 149). CONCLUSIONS: Long-term follow up after combination therapy versus supervised exercise only, demonstrated no significant difference in walking distance or quality of life between the treatment groups. Combination therapy resulted in a lower number of revascularization procedures during follow-up but a higher total number of revascularizations including the randomized treatment. TRIAL REGISTRATION: Netherlands Trial Registry Identifier: NTR2249.

Heart rate variability is associated with left ventricular systolic, diastolic function and incident heart failure in the general population.

BACKGROUND: HRV has mostly shown associations with systolic dysfunction and more recently, with diastolic dysfunction in Heart failure (HF) patients. But the role of sympathetic nervous system in changes of left ventricular (LV) systolic and diastolic function and new-onset HF has not been extensively studied. METHODS: Among 3157 men and 4405 women free of HF and atrial fibrillation retrospectively included from the population-based Rotterdam Study, we used linear mixed models to examine associations of RR-interval differences and standard deviation of RR-intervals corrected for heart rate (RMSSDc and SDNNc) with longitudinal changes of LV ejection fraction (LVEF), E/A ratio, left atrial (LA) diameter, E/e' ratio. Afterwards, using cox regressions, we examined their association with new-onset HF. RESULTS: Mean (SD) age was 65 (9.95) in men and 65.7 (10.2) in women. Every unit increase in log RMSSDc was accompanied by 0.75% (95%CI:-1.11%;-0.39%) and 0.31% (- 0.60%;-0.01%) lower LVEF among men and women each year, respectively. Higher log RMSSDc was linked to 0.03 (- 0.04;-0.01) and 0.02 (- 0.03;-0.003) lower E/A and also - 1.76 (- 2.77;- 0.75) and - 1.18 (- 1.99;-0.38) lower LVM index in both sexes and 0.72 mm (95% CI: - 1.20;-0.25) smaller LA diameters in women. The associations with LVEF in women diminished after excluding HF cases during the first 3 years of follow-up. During a median follow-up of 8.7 years, hazard ratios (95%CI) for incident HF were 1.34 (1.08;1.65) for log RMSSDc in men and 1.15 (0.93;1.42) in women. SDNNc showed similar associations. CONCLUSIONS: Indices of HRV were associated with worse systolic function in men but mainly with improvement in LA size in women. Higher HRV was associated with higher risk of new-onset HF in men. Our findings highlight potential sex differences in autonomic function underlying cardiac dysfunction and heart failure in the general population.

High Impact of Pediatric Inflammatory Bowel Disease on Caregivers' Work Productivity and Daily Activities: An International Prospective Study.

OBJECTIVES: To evaluate the longitudinal evolution of work productivity loss and activity impairment in caregivers of children with inflammatory bowel disease (IBD). We also evaluated the associations between these impairments, IBD-related factors, and caregivers' health-related quality of life (HRQOL) and estimated the indirect costs related to work absenteeism. STUDY DESIGN: Since January 2017, children with newly diagnosed IBD were enrolled prospectively in the Pediatric Inflammatory Bowel Disease Network for Safety, Efficacy, Treatment and Quality improvement of care study. The impact of pediatric-onset IBD on caregivers' socioeconomic functioning (work and daily activities) and HRQOL was assessed using the Work Productivity and Activity Impairment for caregivers questionnaire and the European Quality of Life Five Dimension Five Level questionnaire, at diagnosis and 3 and 12 months of age. Generalized estimating equation models were applied to evaluate outcomes longitudinally, adjusted for IBD type, disease activity, and child's age at diagnosis. RESULTS: Up to July 2021, 491 children with IBD were eligible for analysis of caregivers' Work Productivity and Activity Impairment questionnaire. At diagnosis, the mean caregivers' employment rate was 78.4%; the adjusted mean work productivity loss was 44.6% (95% CI, 40.2%-49.0%), and the adjusted mean activity impairment was 34.3% (95% CI, 30.8%-37.7%). Work productivity loss and activity impairment significantly decreased over time and were associated with disease activity, but not with IBD type or child's age. Caregivers' HRQOL was associated with both impairments. Costs related to work absenteeism were at least €6272 ($7276) per patient during the first year after diagnosis. CONCLUSIONS: Caregivers of children with IBD experience significant impairments in work and daily activities, especially at diagnosis. The impact decreases thereafter and is associated with disease activity and caregivers' HRQOL. Work absenteeism results in high indirect costs.

Modeling the underlying biological processes in Alzheimer's disease using a multivariate competing risk joint model.

Many clinical trials repeatedly measure several longitudinal outcomes on patients. Patient follow-up can discontinue due to an outcome-dependent event, such as clinical diagnosis, death, or dropout. Joint modeling is a popular choice for the analysis of this type of data. Using example data from a prodromal Alzheimer's disease trial, we propose a new type of multivariate joint model in which longitudinal brain imaging outcomes and memory impairment ratings are allowed to be associated both with time to open-label medication and dropout, and where the brain imaging outcomes may also directly affect the memory impairment ratings. Existing joint models for multivariate longitudinal outcomes account for the correlation between the longitudinal outcomes through the random effects, often by assuming a multivariate normal distribution. However, for these models, it is difficult to interpret how the longitudinal outcomes affect each other. We model the dependence between the longitudinal outcomes differently so that a first longitudinal outcome affects a second one. Specifically, for each longitudinal outcome, we use a linear mixed-effects model to estimate its trajectory, where, for the second longitudinal outcome, we include the linear predictor of the first outcome as a time-varying covariate. This facilitates an easy and direct interpretation of the association between the longitudinal outcomes and provides a framework for latent mediation analysis to understand the underlying biological processes. For the trial considered here, we found that part of the intervention effect is mediated through hippocampal brain atrophy. The proposed joint models are fitted using a Bayesian framework via MCMC simulation.

Shared decision making of burdensome surveillance tests using personalized schedules and their burden and benefit.

Benchmark surveillance tests for detecting disease progression (eg, biopsies, endoscopies) in early-stage chronic noncommunicable diseases (eg, cancer, lung diseases) are usually burdensome. For detecting progression timely, patients undergo invasive tests planned in a fixed one-size-fits-all manner (eg, annually). We aim to present personalized test schedules based on the risk of disease progression, that optimize the burden (the number of tests) and the benefit (shorter time delay in detecting progression is better) better than fixed schedules, and enable shared decision making. Our motivation comes from the problem of scheduling biopsies in prostate cancer surveillance. Using joint models for time-to-event and longitudinal data, we consolidate patients' longitudinal data (eg, biomarkers) and results of previous tests, into individualized future cumulative-risk of progression. We then create personalized schedules by planning tests on future visits where the predicted cumulative-risk is above a threshold (eg, 5% risk). We update personalized schedules with data gathered over follow-up. To find the optimal risk threshold, we minimize a utility function of the expected number of tests (burden) and expected time delay in detecting progression (shorter is beneficial) for different thresholds. We estimate these two in a patient-specific manner for following any schedule, by utilizing a patient's predicted risk profile. Patients/doctors can employ these quantities to compare personalized and fixed schedules objectively and make a shared decision of a test schedule.

Using joint models to study the association between CD4 count and the risk of death in TB/HIV data.

BACKGROUND: The association structure linking the longitudinal and survival sub-models is of fundamental importance in the joint modeling framework and the choice of this structure should be made based on the clinical background of the study. However, this information may not always be accessible and rationale for selecting this association structure has received relatively little attention in the literature. To this end, we aim to explore four alternative functional forms of the association structure between the CD4 count and the risk of death and provide rationale for selecting the optimal association structure for our data. We also aim to compare the results obtained from the joint model to those obtained from the time-varying Cox model. METHODS: We used data from the Centre for the AIDS Programme of Research in South Africa (CAPRISA) AIDS Treatment programme, the Starting Antiretroviral Therapy at Three Points in Tuberculosis (SAPiT) study, an open-label, three armed randomised, controlled trial between June 2005 and July 2010 (N=642). In our analysis, we combined the early and late integrated arms and compared results to the sequential arm. We utilized the Deviance Information Criterion (DIC) to select the final model with the best structure, with smaller values indicating better model adjustments to the data. RESULTS: Patient characteristics were similar across the study arms. Combined integrated therapy arms had a reduction of 55% in mortality (HR:0.45, 95% CI:0.28-0.72) compared to the sequential therapy arm. The joint model with a cumulative effects functional form was chosen as the best association structure. In particular, our joint model found that the area under the longitudinal profile of CD4 count was strongly associated with a 21% reduction in mortality (HR:0.79, 95% CI:0.72-0.86). Where as results from the time-varying Cox model showed a 19% reduction in mortality (HR:0.81, 95% CI:0.77-0.84). CONCLUSIONS: In this paper we have shown that the "current value" association structure is not always the best structure that expresses the correct relationship between the outcomes in all settings, which is why it is crucial to explore alternative clinically meaningful association structures that links the longitudinal and survival processes.

Rotterdam Transition Test: A Valid Tool for Monitoring Disease Knowledge in Adolescents With Inflammatory Bowel Disease.

OBJECTIVES: Disease knowledge is important in adolescents with inflammatory bowel disease (IBD) transitioning to adult care. We developed an IBD-specific knowledge questionnaire, the Rotterdam Transition Test (RTT), and aimed to validate this tool. METHODS: This is a prospective longitudinal validation study. The RTT has 25 open questions on IBD, medication, lifestyle, and transition to adult care. A scoring model was developed, and inter-rater agreement was assessed. Using a Rasch model, we determined the difficulty and performance of the questions. Cronbach alpha was used to demonstrate reliability. Patient factors (age, disease, education, medication use, illness acceptance, and independence) were correlated to RTT score. RESULTS: A total of 207 RTTs were evaluated in 111 adolescent IBD patients. The scoring model showed a kappa score of >0.61 for all questions. Reliability with Cronbach alpha was good (0.81). Mean total result of the RTT was 58% (girls) and 55% (boys) of maximal score.The RTT discriminated well between the different levels of knowledge. Knowledge scores increased in patients who did repeated RTTs during the transition period. Male sex, low educational level, disease acceptance issues, and dependence on parents associated with a significantly lower total RTT score. Prednisone use within 3 months and treatment without biologics associated with significantly higher RTT scores. Disease activity was not a significant factor. CONCLUSIONS: The RTT is a reliable and valid tool to assess IBD knowledge. The RTT can be used to detect and discuss knowledge gaps in adolescents with IBD transitioning to adult healthcare.

The use of OCT to detect signs of intracranial hypertension in patients with sagittal suture synostosis: Reference values and correlations.

PURPOSE: To obtain pediatric normative reference values and determine whether optical coherence tomography (OCT) corresponds better with clinical signs of intracranial hypertension (ICH) compared to the traditional screening method fundoscopy in a large cohort of one type of single suture craniosynostosis. METHODS: Control subjects without optic nerve diseases and isolated sagittal synostosis patients aged 3-10 years who underwent fundoscopy and OCT were included in this prospective cohort study. Normative reference values were obtained through bootstrap analysis. Main outcome was the association between peripapillary total retinal thickness (TRT) and total retinal volume (TRV) and appearance on fundoscopy. Signs and symptoms suggestive of ICH, including skull growth arrest, fingerprinting, and headache, were scored. RESULTS: Sixty-four healthy controls and 93 isolated sagittal synostosis patients were included. Normative cut-off values for mean TRT are < 256 µm and > 504 µm and for mean TRV < 0.21 mm3 and > 0.39 mm3. TRT was increased in 16 (17%) and TRV in 15 (16%) of 93 patients, compared to only 4 patients with papilledema on fundoscopy (4%). Both parameters were associated with papilledema on fundoscopy (OR = 16.7, p = 0.02, and OR = 18.2, p = 0.01). Skull growth arrest was significantly associated with abnormal OCT parameters (OR = 13.65, p < 0.01). CONCLUSIONS: The established cut-off points can be applied to screen for ICH in pediatrics. The present study detected abnormalities with OCT more frequent than with fundoscopy, which were associated with skull growth arrest. Therefore, a combination of OCT, fundoscopy, and skull growth arrest can improve clinical decision-making in craniosynostosis.

Dynamic Digital Twin: Diagnosis, Treatment, Prediction, and Prevention of Disease During the Life Course.

A digital twin (DT), originally defined as a virtual representation of a physical asset, system, or process, is a new concept in health care. A DT in health care is not a single technology but a domain-adapted multimodal modeling approach incorporating the acquisition, management, analysis, prediction, and interpretation of data, aiming to improve medical decision-making. However, there are many challenges and barriers that must be overcome before a DT can be used in health care. In this viewpoint paper, we build on the current literature, address these challenges, and describe a dynamic DT in health care for optimizing individual patient health care journeys, specifically for women at risk for cardiovascular complications in the preconception and pregnancy periods and across the life course. We describe how we can commit multiple domains to developing this DT. With our cross-domain definition of the DT, we aim to define future goals, trade-offs, and methods that will guide the development of the dynamic DT and implementation strategies in health care.

Incorporating historical controls in clinical trials with longitudinal outcomes using the modified power prior.

Several dynamic borrowing methods, such as the modified power prior (MPP), the commensurate prior, have been proposed to increase statistical power and reduce the required sample size in clinical trials where comparable historical controls are available. Most methods have focused on cross-sectional endpoints, and appropriate methodology for longitudinal outcomes is lacking. In this study, we extend the MPP to the linear mixed model (LMM). An important question is whether the MPP should use the conditional version of the LMM (given the random effects) or the marginal version (averaged over the distribution of the random effects), which we refer to as the conditional MPP and the marginal MPP, respectively. We evaluated the MPP for one historical control arm via a simulation study and an analysis of the data of Alzheimer's Disease Cooperative Study (ADCS) with the commensurate prior as the comparator. The conditional MPP led to inflated type I error rate when there existed moderate or high between-study heterogeneity. The marginal MPP and the commensurate prior yielded a power gain (3.6%-10.4% vs. 0.6%-4.6%) with the type I error rates close to 5% (5.2%-6.2% vs. 3.8%-6.2%) when the between-study heterogeneity is not excessively high. For the ADCS data, all the borrowing methods improved the precision of estimates and provided the same clinical conclusions. The marginal MPP and the commensurate prior are useful for borrowing historical controls in longitudinal data analysis, while the conditional MPP is not recommended due to inflated type I error rates.