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Featured researches published by Tamar Kraan.


Psychological Medicine | 2016

Cannabis use and transition to psychosis in individuals at ultra-high risk: review and meta-analysis

Tamar Kraan; Laura Koenders; K. Zwaart; Helga K. Ising; D.P.G. van den Berg; L. de Haan; M. van der Gaag

BACKGROUND Previous research has established the relationship between cannabis use and psychotic disorders. Whether cannabis use is related to transition to psychosis in patients at ultra-high risk (UHR) for psychosis remains unclear. The present study aimed to review the existing evidence on the association between cannabis use and transition to psychosis in UHR samples. METHOD A search of PsychInfo, Embase and Medline was conducted from 1996 to August 2015. The search yielded 5559 potentially relevant articles that were selected on title and abstract. Subsequently 36 articles were screened on full text for eligibility. Two random-effects meta-analyses were performed. First, we compared transition rates to psychosis of UHR individuals with lifetime cannabis use with non-cannabis-using UHR individuals. Second, we compared transition rates of UHR individuals with a current DSM-IV cannabis abuse or dependence diagnosis with lifetime users and non-using UHR individuals. RESULTS We found seven prospective studies reporting on lifetime cannabis use in UHR subjects (n = 1171). Of these studies, five also examined current cannabis abuse or dependence. Lifetime cannabis use was not significantly associated with transition to psychosis [odds ratio (OR) 1.14, 95% confidence interval (CI) 0.856-1.524, p = 0.37]. A second meta-analysis yielded an OR of 1.75 (95% CI 1.135-2.710, p = 0.01), indicating a significant association between current cannabis abuse or dependence and transition to psychosis. CONCLUSIONS Our results show that cannabis use was only predictive of transition to psychosis in those who met criteria for cannabis abuse or dependence, tentatively suggesting a dose-response relationship between current cannabis use and transition to psychosis.


Schizophrenia Bulletin | 2016

Four-Year Follow-up of Cognitive Behavioral Therapy in Persons at Ultra-High Risk for Developing Psychosis : The Dutch Early Detection Intervention Evaluation (EDIE-NL) Trial

Helga K. Ising; Tamar Kraan; Judith Rietdijk; Sara Dragt; Rianne M. C. Klaassen; Nynke Boonstra; Dorien H. Nieman; Monique Willebrands-Mendrik; David P. G. van den Berg; Don Linszen; Lex Wunderink; Wim Veling; Filip Smit; Mark van der Gaag

BACKGROUND Previously, we demonstrated that cognitive behavior therapy for ultra-high risk (called CBTuhr) halved the incidence of psychosis over an 18-month period. Follow-up data from the same study are used to evaluate the longer-term effects at 4 years post-baseline. METHOD The Dutch Early Detection and Intervention Evaluation study was a randomized controlled trial of 196 UHR patients comparing CBTuhr with treatment-as-usual (TAU) for comorbid disorders with TAU only. Of the original 196 patients, 113 consented to a 4-year follow-up (57.7%; CBTuhr = 56 vs TAU = 57). Over the study period, psychosis incidence, remission from UHR status, and the effects of transition to psychosis were evaluated. RESULTS The number of participants in the CBTuhr group making the transition to psychosis increased from 10 at 18-month follow-up to 12 at 4-year follow-up whereas it did not change in the TAU group (n = 22); this still represents a clinically important (incidence rate ratio [IRR] = 12/22 = 0.55) and significant effect (F(1,5) = 8.09, P = .03), favoring CBTuhr. The odds ratio of CBTuhr compared to TAU was 0.44 (95% CI: 0.24-0.82) and the number needed to treat was 8. Moreover, significantly more patients remitted from their UHR status in the CBTuhr group (76.3%) compared with the TAU group (58.7%) [t(120) = 2.08, P = .04]. Importantly, transition to psychosis was associated with more severe psychopathology and social functioning at 4-year follow-up. CONCLUSIONS CBTuhr to prevent a first episode of psychosis in persons at UHR of developing psychosis is still effective at 4-year follow-up. Our data also show that individuals meeting the formal criteria of a psychotic disorder have worse functional and social outcomes compared with non-transitioned cases. TRIAL REGISTRATION The trial is registered at Current Controlled Trials as trial number ISRCTN21353122 (http://controlled-trials.com/ISRCTN21353122/gaag).


Psychiatry Research-neuroimaging | 2017

The effect of childhood adversity on 4-year outcome in individuals at ultra high risk for psychosis in the Dutch Early Detection Intervention Evaluation (EDIE-NL) Trial

Tamar Kraan; Helga K. Ising; Marjolein Fokkema; David P. G. van den Berg; Margot Kerkhoven; Wim Veling; Filip Smit; Don Linszen; Dorien H. Nieman; Lex Wunderink; Nynke Boonstra; Rianne Klaassen; Sara Dragt; Judith Rietdijk; Lieuwe de Haan; Mark van der Gaag

Childhood adversity is associated with a range of mental disorders, functional impairment and higher health care costs in adulthood. In this study we evaluated if childhood adversity was predictive of adverse clinical and functional outcomes and health care costs in a sample of patients at ultra-high risk (UHR) for developing a psychosis. Structural Equation Modeling was used to examine the effect of childhood adversity on depression, anxiety, transition to psychosis and overall functioning at 4-year follow-up. In addition, we evaluated economic costs of childhood adversity in terms of health care use and productivity loss. Data pertain to 105 UHR participants of the Dutch Early Detection and Intervention Evaluation (EDIE-NL). Physical abuse was associated with higher depression rates (b=0.381, p=0.012) and lower social functional outcome (b=-0.219, p=0.017) at 4-year follow-up. In addition, emotional neglect was negatively associated with social functioning (b=-0.313, p=0.018). We did not find evidence that childhood adversity was associated with transition to psychosis, but the experience of childhood adversity was associated with excess health care costs at follow-up. The data indicate long-term negative effects of childhood adversity on depression, social functioning and health care costs at follow-up in a sample of UHR patients.


Schizophrenia Bulletin | 2016

Four-Year Cost-effectiveness of Cognitive Behavior Therapy for Preventing First-episode Psychosis: The Dutch Early Detection Intervention Evaluation (EDIE-NL) Trial

Helga K. Ising; Joran Lokkerbol; Judith Rietdijk; Sara Dragt; Rianne M. C. Klaassen; Tamar Kraan; Nynke Boonstra; Dorien H. Nieman; David P. G. van den Berg; Don Linszen; Lex Wunderink; Wim Veling; Filip Smit; Mark van der Gaag

Background This study aims to evaluate the long-term cost-effectiveness of add-on cognitive behavior therapy (CBT) for the prevention of psychosis for individuals at ultrahigh risk (UHR) of psychosis. Method The Dutch Early Detection and Intervention randomized controlled trial was used, comparing routine care (RC; n = 101) with routine care plus CBT for UHR (here called CBTuhr; n = 95). A cost-effectiveness analysis was conducted with treatment response (defined as proportion of averted transitions to psychosis) as an outcome and a cost-utility analysis with quality-adjusted life years (QALYs) gained as a secondary outcome. Results The proportion of averted transitions to psychosis was significantly higher in the CBTuhr condition (with a risk difference of 0.122; b = 1.324, SEb = 0.017, z = 7.99, P < 0.001). CBTuhr showed an 83% probability of being more effective and less costly than RC by -US


Schizophrenia Bulletin | 2018

Child Maltreatment and Clinical Outcome in Individuals at Ultra-High Risk for Psychosis in the EU-GEI High Risk Study

Tamar Kraan; Manouk Themmen; Lucia Valmaggia; Matthew J. Kempton; P.K. McGuire; Jim van Os; Bart P.F. Rutten; Filip Smit; Lieuwe de Haan; Mark van der Gaag; Eu-Gei High Risk Study

5777 (savings) per participant. In addition, over the 4-year follow-up period, cumulative QALY health gains were marginally (but not significantly) higher in CBTuhr than for RC (2.63 vs. 2.46) and the CBTuhr intervention had a 75% probability of being the superior treatment (more QALY gains at lower costs) and a 92% probability of being cost-effective compared with RC at the Dutch threshold value (US


European Journal of Psychotraumatology | 2016

Exposing therapists to trauma-focused treatment in psychosis: effects on credibility, expected burden, and harm expectancies

David P. G. van den Berg; Berber M. van der Vleugel; Paul A.J.M. de Bont; Gwen Thijssen; Carlijn de Roos; Rianne A. de Kleine; Tamar Kraan; Helga K. Ising; Ad de Jongh; Agnes van Minnen; Mark van der Gaag

24 560; €20 000 per QALY). Conclusions Add-on preventive CBTuhr had a high likelihood (83%) of resulting in more averted transitions to psychosis and lower costs as compared with RC. In addition, the intervention had a high likelihood (75%) of resulting in more QALY gains and lower costs as compared to RC.


Schizophrenia Research | 2016

Predicting trauma-focused treatment outcome in psychosis

David P. G. van den Berg; Berber M. van der Vleugel; Paul A.J.M. de Bont; A.B.P. Staring; Tamar Kraan; Helga K. Ising; Carlijn de Roos; Ad de Jongh; Agnes van Minnen; Mark van der Gaag

Background Child maltreatment has been associated with a wide range of mental disorders in adulthood. Whether child maltreatment is specifically associated with psychosis risk in individuals at ultra-high risk (UHR) for psychosis, or leads to a general vulnerability for overall psychopathology in the UHR stage remains unclear. The present study examines the association between child maltreatment and transition to psychosis and other mental disorders. Methods The sample consisted of 259 UHR individuals from the EUropean network of national schizophrenia networks studying Gene-Environment Interactions (EU-GEI) study. Participants were followed-up for 2 years to assess clinical outcome. Clinical outcome was assessed at 6 months, 12 months, and 24 months after baseline. Child maltreatment before the age of 17 years was assessed at baseline. Results Our findings show that a history of emotional abuse was associated with an increased risk for transition to psychosis (OR = 3.78, 95% CI = 1.17 to 12.39, P = .027). Apart from psychosis, a history of physical abuse was associated with depressive disorder (OR = 4.92, 95% CI = 2.12 to 11.39, P = .001), post-traumatic stress disorder (OR = 2.06, 95% CI = 1.10 to 3.86, P = .023), panic disorder (OR = 2.00, 95% CI = 1.00 to 3.99, P = .048) and social phobia (OR = 2.47, 95% CI = 1.18 to 5.16, P = .016) at follow-up. Conclusion Our findings suggest that in the UHR stage child maltreatment is a pluripotent risk factor for developing psychosis, depressive disorder, post-traumatic stress disorder (PTSD), panic disorder, and social phobia in adulthood.


Schizophrenia Research | 2015

Trauma and recent life events in individuals at ultra high risk for psychosis: Review and meta-analysis

Tamar Kraan; Filip Smit; Lieuwe de Haan; Mark van der Gaag

Background Despite robust empirical support for the efficacy of trauma-focused treatments, the dissemination proves difficult, especially in relation to patients with comorbid psychosis. Many therapists endorse negative beliefs about the credibility, burden, and harm of such treatment. Objective This feasibility study explores the impact of specialized training on therapists’ beliefs about trauma-focused treatment within a randomized controlled trial. Method Therapist-rated (n=16) credibility, expected burden, and harm expectancies of trauma-focused treatment were assessed at baseline, post-theoretical training, post-technical training, post-supervised practical training, and at 2-year follow-up. Credibility and burden beliefs of therapists concerning the treatment of every specific patient in the trial were also assessed. Results Over time, therapist-rated credibility of trauma-focused treatment showed a significant increase, whereas therapists’ expected burden and harm expectancies decreased significantly. In treating posttraumatic stress disorder (PTSD) in patients with psychotic disorders (n=79), pre-treatment symptom severity was not associated with therapist-rated credibility or expected burden of that specific treatment. Treatment outcome had no influence on patient-specific credibility or burden expectancies of therapists. Conclusions These findings support the notion that specialized training, including practical training with supervision, has long-term positive effects on therapists’ credibility, burden, and harm beliefs concerning trauma-focused treatment. Highlights of the article Specialized training improved therapists’ credibility, burden, and harm beliefs. Patients’ symptom severity and treatment outcome did not affect these beliefs. Replication of our findings in larger cohorts with a control group is warranted.


Schizophrenia Research | 2015

Childhood trauma and clinical outcome in patients at ultra-high risk of transition to psychosis

Tamar Kraan; Daniella S. van Dam; Esther L. de Ruigh; Dorien H. Nieman; Sarah Durston; Patricia F. Schothorst; Mark van der Gaag; Lieuwe de Haan

OBJECTIVE Although TF treatments are effective in patients with psychosis, it is unknown whether specific psychosis-related obstacles limit the effects, and what determines good outcome. METHODS Baseline posttraumatic stress disorder (PTSD) symptom severity and seven psychosis-specific variables were tested as predictors in patients with a psychotic disorder and PTSD (n=108), who received eight sessions of TF treatment (Prolonged Exposure, or Eye Movement Desensitization and Reprocessing therapy) in a single-blind randomized controlled trial. Multiple regression analyses were performed. RESULTS Baseline PTSD symptom severity was significantly associated with posttreatment PTSD symptom severity, explaining 11.4% of the variance. Additionally, more severe PTSD at baseline was also significantly associated with greater PTSD symptom improvement during treatment. After correction for baseline PTSD symptom severity, the model with the seven baseline variables did not significantly explain the variance in posttreatment PTSD outcome. Within this non-significant model, the presence of auditory verbal hallucinations contributed uniquely to posttreatment outcome but explained little variance (5.4%). Treatment completers and dropouts showed no significant difference on any of the psychosis-related variables. CONCLUSIONS Given the low predictive utility of baseline psychosis-related factors, we conclude that there is no evidence-based reason to exclude patients with psychotic disorders from TF treatments. Also, we speculate that patients with psychosis and severe baseline PTSD might derive more benefit if given more than eight sessions. Trial registration current controlled-trials.com | Identifier: ISRCTN79584912 | http://www.isrctn.com/ISRCTN79584912.


Psychological Medicine | 2016

Disentangling cause and effect in the relationship between cannabis and psychosis: are we there yet? Reply

Tamar Kraan; Lieuwe de Haan; M. van der Gaag

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Filip Smit

VU University Amsterdam

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Nynke Boonstra

University Medical Center Groningen

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Sara Dragt

University of Amsterdam

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