Incidence, prevalence and survival in patients with Langerhans cell histiocytosis: A national registry study from England, 2013-2019.

This analysis is the largest population-based study to date to provide contemporary and comprehensive epidemiological estimates of all third edition of the International Classification of Diseases for Oncology (ICD-O-3) coded Langerhans cell histiocytosis (LCH) from England. People of all ages were identified from the National Cancer Registration Dataset using ICD-O-3 morphologies 9751-9754 for neoplasms diagnosed in 2013-2019. A total of 658 patients were identified, of whom 324 (49%) were children aged <15 years. The age-standardised incidence rate was 4.46 (95% confidence interval [CI] 3.99-4.98) per million children and 1.06 (95% CI 0.94-1.18) per million adults aged ≥15 years. Prevalence of LCH was 9.95 (95% CI 9.14-10.81) per million persons at the end of 2019. The 1-year overall survival (OS) was 99% (95% CI 97%-100%) for children and 90% (95% CI 87%-93%) for adults. Those aged ≥60 years had poorer OS than those aged <15 years (hazard ratio [HR] 22.12, 95% CI 7.10-68.94; p < 0.001). People in deprived areas had lower OS than those in the least deprived areas (HR 5.36, 95% CI 1.16-24.87; p = 0.03). There will inevitably be other environmental factors and associations yet to be identified, and the continued standardised data collection will allow further evaluation of data over time. This will be increasingly important with developments in LCH management following the large collaborative international trials such as LCH IV.

Incidence and survival of haemophagocytic lymphohistiocytosis: A population-based cohort study from England.

BACKGROUND: Haemophagocytic lymphohistiocytosis (HLH) is a rare hyper-inflammatory condition with poor outcomes. OBJECTIVES: Few population-based estimates of the incidence and survival in adults exist. We aimed to provide these data for England. METHODS: We used population-based linked data from primary care, secondary care, cancer registries and mortality databases in England to identify people diagnosed with HLH between 1 January 2000 and 31 December 2016. We calculated annual incidence rates by age and sex, modelled change in incidence over time with Poisson regression, calculated overall 1-year survival using Kaplan-Meier methods and estimated adjusted hazard ratios (HRs) of death using a Cox proportional hazards model. RESULTS: We identified 214 patients with HLH. The reported age and sex-adjusted incidence increased twofold over the period, from around one to around two per million. Incidence was highest in those below 1 year (14.6 per million) and ≥75 years (2.2 per million), and lowest in those aged 15-44 years (0.8 per million). One-year survival varied by age and sex from 77% (95% confidence interval [CI] 63%-86%) in those <15 years to 30% (95% CI 14%-49%) in those ≥75. In patients with haematological cancer, the adjusted HR for death was 2.60 (95% CI 1.45-4.66) compared to patients with no malignant or rheumatological disease. CONCLUSION: The incidence of HLH diagnosis in England has increased between 2000 and 2016 and occurs in all ages with varying underlying diseases. One-year survival varies substantially, being particularly poor in those aged over 75 years and those with haematological malignancy.

A validation study of the identification of haemophagocytic lymphohistiocytosis in England using population-based health data.

We assessed the validity of coded healthcare data to identify cases of haemophagocytic lymphohistiocytosis (HLH). Hospital Episode Statistics (HES) identified 127 cases within five hospital Trusts 2013-2018 using ICD-10 codes D76.1, D76.2 and D76.3. Hospital records were reviewed to validate diagnoses. Out of 74 patients, 73 were coded D76.1 or D76.2 (positive predictive value 89·0% [95% Confidence Interval {CI} 80·2-94·9%]) with confirmed/probable HLH. For cases considered not HLH, 44/53 were coded D76.3 (negative predictive value 97·8% [95% CI 88·2-99·9%]). D76.1 or D76.2 had 68% sensitivity in detecting HLH compared to an established active case-finding HLH register in Sheffield. Office for National Statistics (ONS) mortality data (2003-2018) identified 698 patients coded D76.1, D76.2 and D76.3 on death certificates. Five hundred and forty-one were coded D76.1 or D76.2 of whom 524 (96·9%) had HLH in the free-text cause of death. Of 157 coded D76.3, 66 (42·0%) had HLH in free text. D76.1 and D76.2 codes reliably identify HLH cases, and provide a lower bound on incidence. Non-concordance between D76.3 and HLH excludes D76.3 as an ascertainment source from HES. Our results suggest electronic healthcare data in England can enable population-wide registration and analysis of HLH for future research.

Additive Prognostic Impact of Gastrointestinal Involvement in Severe Multisystem Langerhans Cell Histiocytosis.

OBJECTIVE: To evaluate the prognostic impact of gastrointestinal involvement on the survival of children with Langerhans cell histiocytosis (GI-LCH) registered with the international clinical trials of the Histiocyte Society. STUDY DESIGN: This was a retrospective analysis of 2414 pediatric patients registered onto the consecutive trials DAL-HX 83, DAL-HX 90, LCH-I, LCH-II, and LCH-III. RESULTS: Among the 1289 patients with single-system LCH, there was no single case confined to the GI tract; 114 of 1125 (10%) patients with multisystem LCH (MS-LCH) had GI-LCH at initial presentation. GI-LCH was significantly more common in children aged <2 years at diagnosis (13% vs 6% in those aged >2 years; P < .001) and in those with risk organ involvement (15% vs 6% in those without risk organ involvement; P < .001). The 5-year overall survival (OS) in patients without risk organ involvement was excellent irrespective of GI disease (98% vs 97% in patients with GI-LCH; P = .789). In patients with risk organ involvement, the 5-year OS was 51% in 70 patients with GI-LCH vs 72% in 394 patients without GI-LCH (P < .001). CONCLUSIONS: GI-LCH has an additive unfavorable prognostic impact in children with MS-LCH and risk organ involvement. The emerding need for more intensive or alternative treatments mandates prospective evaluation.

Confirmed efficacy of etoposide and dexamethasone in HLH treatment: long-term results of the cooperative HLH-2004 study.

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome comprising familial/genetic HLH (FHL) and secondary HLH. In the HLH-94 study, with an estimated 5-year probability of survival (pSu) of 54% (95% confidence interval, 48%-60%), systemic therapy included etoposide, dexamethasone, and, from week 9, cyclosporine A (CSA). Hematopoietic stem cell transplantation (HSCT) was indicated in patients with familial/genetic, relapsing, or severe/persistent disease. In HLH-2004, CSA was instead administered upfront, aiming to reduce pre-HSCT mortality and morbidity. From 2004 to 2011, 369 children aged <18 years fulfilled HLH-2004 inclusion criteria (5 of 8 diagnostic criteria, affected siblings, and/or molecular diagnosis in FHL-causative genes). At median follow-up of 5.2 years, 230 of 369 patients (62%) were alive (5-year pSu, 61%; 56%-67%). Five-year pSu in children with (n = 168) and without (n = 201) family history/genetically verified FHL was 59% (52%-67%) and 64% (57%-71%), respectively (familial occurrence [n = 47], 58% [45%-75%]). Comparing with historical data (HLH-94), using HLH-94 inclusion criteria, pre-HSCT mortality was nonsignificantly reduced from 27% to 19% (P = .064 adjusted for age and sex). Time from start of therapy to HSCT was shorter compared with HLH-94 (P =020 adjusted for age and sex) and reported neurological alterations at HSCT were 22% in HLH-94 and 17% in HLH-2004 (using HLH-94 inclusion criteria). Five-year pSu post-HSCT overall was 66% (verified FHL, 70% [63%-78%]). Additional analyses provided specific suggestions on potential pre-HSCT treatment improvements. HLH-2004 confirms that a majority of patients may be rescued by the etoposide/dexamethasone combination but intensification with CSA upfront, adding corticosteroids to intrathecal therapy, and reduced time to HSCT did not improve outcome significantly.

Haematopoietic stem cell transplantation for refractory Langerhans cell histiocytosis: outcome by intensity of conditioning.

Patients with Langerhans cell histiocytosis (LCH) refractory to conventional chemotherapy have a poor outcome. There are currently two promising treatment strategies for high-risk patients: the first involves the combination of 2-chlorodeoxyadenosine and cytarabine; the other approach is allogeneic haematopoietic stem cell transplantation (HSCT). Here we evaluated 87 patients with high-risk LCH who were transplanted between 1990 and 2013. Prior to the year 2000, most patients underwent HSCT following myeloablative conditioning (MAC): only 5 of 20 patients (25%) survived with a high rate (55%) of transplant-related mortality (TRM). After the year 2000 an increasing number of patients underwent HSCT with reduced intensity conditioning (RIC): 49/67 (73%) patients survived, however, the improved survival was not overtly achieved by the introduction of RIC regimens with similar 3-year probability of survival after MAC (77%) and RIC transplantation (71%). There was no significant difference in TRM by conditioning regimen intensity but relapse rates were higher after RIC compared to MAC regimens (28% vs. 8%, P = 0·02), although most patients relapsing after RIC transplantation could be salvaged with further chemotherapy. HSCT may be a curative approach in 3 out of 4 patients with high risk LCH refractory to chemotherapy: the optimal choice of HSCT conditioning remains uncertain.

Langerhans cell histiocytosis (LCH): guidelines for diagnosis, clinical work-up, and treatment for patients till the age of 18 years.

These guidelines for the management of patients up to 18 years with Langerhans cell histiocytosis (LCH) have been set up by a group of experts involved in the Euro Histio Net project who participated in national or international studies and in peer reviewed publications. Existing guidelines were reviewed and changed where new evidence was available in the literature up to 2012. Data and publications have been ranked according to evidence based medicine and when there was a lack of published data, consensus between experts was sought. Guidelines for diagnosis, initial clinical work-up, and treatment and long-term follow-up of LCH patients are presented.

1-year survival in haemophagocytic lymphohistiocytosis: a nationwide cohort study from England 2003-2018.

Haemophagocytic lymphohistiocytosis (HLH) is a lethal syndrome of excessive immune activation. We undertook a nationwide study in England of all cases of HLH diagnosed between 2003 and 2018, using linked electronic health data from hospital admissions and death certification. We modelled interactions between demographics and comorbidities and estimated one-year survival by calendar year, age group, gender and comorbidity (haematological malignancy, auto-immune, other malignancy) using Cox regression. There were 1628 people with HLH identified. Overall, crude one-year survival was 50% (95% Confidence interval 48-53%) which varied substantially with age (0-4: 61%; 5-14: 76%; 15-54: 61%; > 55: 24% p < 0.01), sex (males, 46%, worse than females, 55% p < 0.01) and associated comorbidity (auto-immune, 69%, haematological malignancy 28%, any other malignancy, 37% p < 0.01). Those aged < 54 years had a threefold increased risk of death at 1-year amongst HLH associated with malignancy compared to auto-immune. However, predicted 1-year survival decreased markedly with age in those with auto-immune (age 0-14, 84%; 15-54, 73%; > 55, 27%) such that among those > 55 years, survival was as poor as for patients with haematological malignancy. One-year survival following a diagnosis of HLH varies considerably by age, gender and associated comorbidity. Survival was better in those with auto-immune diseases among the young and middle age groups compared to those with an underlying malignancy, whereas in older age groups survival was uniformly poor regardless of the underlying disease process.

Langerhans cell histiocytosis and associated malignancies: A retrospective analysis of 270 patients.

PURPOSE: The frequency of Langerhans cell histiocytosis (LCH) and associated malignancies (AM) is greater than statistically expected. Here, we analyze LCH-AM co-occurrence in both children and adults. METHODS: Between 1991 and 2015, data were collected by regular questionnaires to members of the Histiocyte Society and searches in PubMed and Abstract Books. Patients were grouped by age at LCH diagnosis (≤ and >18 years), and types and timing of AM occurrence were plotted with respect to the LCH diagnosis. For the statistical analysis, only the first AM were considered. RESULTS: A total of 285 LCH-AM in 270 patients were identified, 116 (43%) ≤ 18 years, and 154 (57%) >18 years. In childhood LCH-AM pairs, leukemias and myeloproliferative disorders (n = 58; 50.0%) prevailed over solid tumors (n = 43; 37.1%) and lymphoma (n = 15; 12.9%). In adults, solid tumors were reported in 61 patients (39.6%), lymphoma, and leukemias and myeloproliferative disorders in 56 (36.4%) and 37 (24.0%) patients, respectively. In most children, AM followed LCH (n = 69, 59.5%), whereas in adults, LCH and AM occurred concurrently in 69 patients (44.8%). In children, T-lineage acute lymphoblastic leukemia (ALL) and promyelocytic acute myeloid leukemia (AML) and retinoblastoma were over-represented and thyroid carcinoma in adults. CONCLUSIONS: The largest collection of data on LCH-AM to date clearly indicates inherent relationships between specific types of AM and LCH, which may be due to therapy effects, clonal evolution, and germ-line predisposition, respectively. Prospective thorough genetic analysis is warranted and will hopefully shed light on the association of LCH and second neoplasms.

The international dataset on the association between Langerhans Cell Histiocytosis and other malignancies.

This article presents the international dataset of cases in which the association of Langerhans cell Histiocytosis (LCH) with other malignancies (AM) was documented occurring at any age before, concurrently or after LCH. These data are mostly derived from previously published manuscripts or from completed case report forms (CRFs) by Histiocyte Society (HS) members or colleagues. In particular, for each case of LCH-AM, the database reports all the available data about clinical and biologic characteristics of the two tumors, as well about treatment and status at follow-up. The AM were categorized as: i) leukemias [acute lymphoblastic or myeloid leukemia (ALL and AML, respectively), other leukemias] and myeloproliferative disorders; ii) lymphomas [Hodgkin lymphoma (HL) and non-Hodgkin lymphomas (NHL)] and iii) solid tumors. A total of 270 LCH-AM cases were documented, of which 116 (43%) occurred among children. After stratification by age at LCH diagnosis, using 18 years as cut-off between children and adults, we here provide details on the clinical characteristics in terms of LCH system involvement and affected organs, as well on the temporal relationship between the LCH and AM diagnoses, including details on the AM malignancy types. In 19 cases the LCH and the corresponding AM occurred in a different age group. The data set is available for future studies in view of new insights of the genetic or environmental determinants of LCH and/or of treatment related subsequent neoplasms.

Temporal Trends in the Incidence of Hemophagocytic Lymphohistiocytosis: A Nationwide Cohort Study From England 2003-2018.

Hemophagocytic lymphohistiocytosis (HLH) is rare, results in high mortality, and is increasingly being diagnosed. We aimed to quantify the incidence of diagnosed HLH and examine temporal trends in relation to age and associated diseases. Using national linked electronic health data from hospital admissions and death certification cases of HLH that were diagnosed in England between January 1, 2003, and December 31, 2018. We calculated incidence rates of diagnosed HLH per million population by calendar year, age group, sex, and associated comorbidity (hematological malignancy, inflammatory rheumatological or bowel diseases [IBD]). We modeled trends in incidence and the interactions between calendar year, age, and associated comorbidity using Poisson regression. There were 1674 people with HLH diagnosed in England between 2003 and 2018. The incidence rate quadrupled (incidence rate ratio [IRR] 2018 compared to 2003: 3.88, 95% confidence interval [CI] 2.91 to 5.28), increasing 11% annually (adjusted IRR 1.11, 95% CI 1.09 to 1.12). There was a transition across age groups with greater increases in those aged 5-14 years of HLH associated with rheumatological disease/IBD compared with hematological malignancy, with similar increases in HLH associated with both comorbidities for those 15-54, and greater increases in HLH associated with hematological malignancies for those 55 years and older. The incidence of HLH in England has quadrupled between 2003 and 2018. Substantial variation in the incidence occurred with inflammatory rheumatological diseases/IBD-associated HLH increasing more among the younger age groups, whereas in older age groups, the largest increase was seen with hematological malignancy-associated HLH.

Superior vena cava obstruction: dangers of a missed diagnosis.

We report the case of a 7 year old girl who presented to the Children's Emergency Department with a 6 week history of bilateral facial and neck swelling. She had felt generally unwell, tired, with a recent onset of dry cough, and had presented multiple times to her general practitioner (GP) who after initially unsuccessfully trying an antihistamine, had given her five courses of soluble Betamethasone (corticosteroid) over six weeks, for presumed allergy; this temporarily relieved her symptoms for a couple of days each time. On subsequent referral to Accident and Emergency she was found to have a superior mediastinal mass, with a left pleural effusion and mediastinal deviation to the right. Further investigation confirmed the diagnosis of a T-cell lymphoma causing superior vena cava obstruction of blood flow through the SVC to the right atrium and is a classical oncological emergency. This case report highlights the importance of recognizing superior vena cava obstruction and the need for awareness of malignancy as a differential diagnosis when initially presented with a child with non-specific respiratory findings. We highlight that acute tumour lysis syndrome, a life threatening metabolic emergency that results from massive cytolysis of malignant cells, may occur after a single dose of corticosteroids and one should be aware of this potentially life-threatening complication.

Management of children and young people with idiopathic pituitary stalk thickening, central diabetes insipidus, or both: a national clinical practice consensus guideline.

Unexplained or idiopathic pituitary stalk thickening or central diabetes insipidus not only harbours rare occult malignancies in 40% of cases but can also reflect benign congenital defects. Between 2014 and 2019, a multidisciplinary, expert national guideline development group in the UK systematically developed a management flowchart and clinical practice guideline to inform specialist care and improve outcomes in children and young people (aged <19 years) with idiopathic pituitary stalk thickening, central diabetes insipidus, or both. All such cases of idiopathic pituitary stalk thickening and central diabetes insipidus require dynamic pituitary function testing, specialist pituitary imaging, measurement of serum ß-human chorionic gonadotropin and alpha-fetoprotein concentrations, chest x-ray, abdominal ultrasonography, optometry, and skeletal survey for occult disease. Stalk thickening of 4 mm or more at the optic chiasm, 3 mm or more at pituitary insertion, or both, is potentially pathological, particularly if an endocrinopathy or visual impairment coexists. In this guideline, we define the role of surveillance, cerebrospinal fluid tumour markers, whole-body imaging, indications, timing and risks of stalk biopsy, and criteria for discharge. We encourage a registry of outcomes to validate the systematic approach described in this guideline and research to establish typical paediatric stalk sizes and the possible role of novel biomarkers, imaging techniques, or both, in diagnosis.

Paediatric presentation of familial cerebral cavernoma.

We report the case of a 13-year-old male who presented with headaches and was presumed to have a brain tumour. He was subsequently found to have multiple cerebral cavernomas with haemorrhage and positive family history. We review the literature on familial cavernomas. Cerebral cavernous malformations (CCMs) are characterized by abnormally enlarged capillary cavities without intervening brain parenchyma [Verlaan et al. Neurology 2005; 65:1982-1983] that may involve any part of the central nervous system. Focal neurologic deficit and haemorrhage occur in 45% of children, higher than in adults [Stoeter. Neurosurg Rev 2001; 24]. Paediatric patients with symptomatic cavernous malformations should be treated surgically because of the risk of haemorrhage [Lee et al. Child's Nervous Syst 2008; 24:321-327].

High incidence of hearing loss in long-term survivors of multisystem Langerhans cell histiocytosis.

BACKGROUND: Ear involvement in the acute phase of Langerhans cell histiocytosis (LCH) is commonly seen and well documented, but the long-term sequelae are less well described, particularly in relation to hearing loss. METHODS: We investigated 40 patients with biopsy-proven multisystem LCH >5 years from the end of treatment, using detailed audiological assessment and CT/MRI imaging of the petrous temporal bones. RESULTS: The incidence of ear involvement in the acute phase of disease was 70%. Fifteen of the 39 patients tested (38%) had residual permanent hearing loss at long-term follow-up. CONCLUSIONS: The incidence of hearing loss is much higher than has previously been reported in LCH, and may reflect a referral bias of young (<2 years) and more complex patients to our tertiary centre. However, the hearing loss appears to be highly specific to this patient group when compared to other long-term survivors of childhood cancers, probably due to the propensity of LCH to involve the ears. We therefore recommend audiology testing as an important part of long-term follow-up for patients with multisystem LCH.

Stem cell transplantation for children with hemophagocytic lymphohistiocytosis: results from the HLH-2004 study.

We report the largest prospective study thus far on hematopoietic stem cell transplantation (HSCT) in hemophagocytic lymphohistiocytosis (HLH), a life-threatening hyperinflammatory syndrome comprising familial/genetic HLH (FHL) and secondary HLH. Although all patients with HLH typically need intensive anti-inflammatory therapy, patients with FHL also need HSCT to be cured. In the international HLH-2004 study, 187 children aged <18 years fulfilling the study inclusion criteria (5 of 8 diagnostic criteria, affected sibling, or molecular diagnosis in FHL-causative genes) underwent 209 transplants (2004-2012), defined as indicated in patients with familial/genetic, relapsing, or severe/persistent disease. Five-year overall survival (OS) post-HSCT was 66% (95% confidence interval [CI], 59-72); event-free survival (EFS) was 60% (95% CI, 52-67). Five-year OS was 81% (95% CI, 65-90) for children with a complete response and 59% (95% CI, 48-69) for those with a partial response (hazard ratio [HR], 2.12; 95% CI, 1.06-4.27; P = .035). For children with verified FHL (family history/genetically verified, n = 134), 5-year OS was 71% (95% CI, 62-78) and EFS was 62% (95% CI, 54-70); 5-year OS for children without verified FHL (n = 53) was significantly lower (52%; 95% CI, 38-65) (P = .040; HR, 1.69; 95% CI, 1.03-2.77); they were also significantly older. Notably, 20 (38%) of 53 patients without verified FHL had natural killer cell activity reported as normal at diagnosis, after 2 months, or at HSCT, suggestive of secondary HLH; and in addition 14 (26%) of these 53 children had no evidence of biallelic mutations despite having 3 or 4 FHL genes analyzed (natural killer cell activity not analyzed after 2 months or at HSCT). We conclude that post-HSCT survival in FHL remains suboptimal, and that the FHL diagnosis should be carefully investigated before HSCT. Pretransplant complete remission is beneficial but not mandatory to achieve post-HSCT survival. This trial was registered at www.clinicaltrials.gov as #NCT00426101.

Management of severe pulmonary Langerhans cell histiocytosis in children.

Patients with pulmonary Langerhans cell histiocytosis (LCH) typically have a benign course but may have extensive cystic lung disease with rare life-threatening complications including multiple and recurrent pneumothoraces and respiratory failure. We report seven severely affected pediatric patients treated with chemotherapy, aggressive chest tube management, and pleurodesis of whom five survived. Patients with extraordinary amounts of pulmonary cystic disease and multiple pneumothoraces due to LCH can have remarkable, curative outcomes with early recognition, optimal LCH-directed therapy, and supportive care.

Long term morbidity and health related quality of life after multi-system Langerhans cell histiocytosis.

BACKGROUND: Langerhans' cell histiocytosis, a clonal multisystem disorder, can affect children or adults resulting in long term sequelae. However, the overall morbidity for survivors has not been formally determined. PATIENTS AND METHODS: We performed a cross-sectional study of 40 unselected long term survivors of childhood multisystem Langerhans cell histiocytosis, involving clinical examination, health-related quality of life assessment, brain imaging, neuropsychometry, endocrine assessment, respiratory function tests and audiometry. A specific 'morbidity score' was devised to measure outcome. RESULTS: Seventy-five percent of patients had detectable long term sequelae, hypothalamic-pituitary dysfunction (50%), cognitive dysfunction (20%) and cerebellar involvement (17.5%) being the most common. Half had moderate to severe morbidity, and the worst-affected patients were unable to lead an independent adult life. Health-related quality of life, which correlated well with the morbidity score (p<0.001), was adversely affected in >50% of patients. CONCLUSION: Organ damage from multisystem Langerhans cell histiocytosis causes long term morbidity extending into adult life. Carefully planned, multidisciplinary follow up is essential to ensure early recognition of problems with appropriate interventions to reduce the impact on patients' 'quality of life'.

Diagnostic omission errors in acute paediatric practice: impact of a reminder system on decision-making.

BACKGROUND: Diagnostic error is a significant problem in specialities characterised by diagnostic uncertainty such as primary care, emergency medicine and paediatrics. Despite wide-spread availability, computerised aids have not been shown to significantly improve diagnostic decision-making in a real world environment, mainly due to the need for prolonged system consultation. In this study performed in the clinical environment, we used a Web-based diagnostic reminder system that provided rapid advice with free text data entry to examine its impact on clinicians' decisions in an acute paediatric setting during assessments characterised by diagnostic uncertainty. METHODS: Junior doctors working over a 5-month period at four paediatric ambulatory units consulted the Web-based diagnostic aid when they felt the need for diagnostic assistance. Subjects recorded their clinical decisions for patients (differential diagnosis, test-ordering and treatment) before and after system consultation. An expert panel of four paediatric consultants independently suggested clinically significant decisions indicating an appropriate and 'safe' assessment. The primary outcome measure was change in the proportion of 'unsafe' workups by subjects during patient assessment. A more sensitive evaluation of impact was performed using specific validated quality scores. Adverse effects of consultation on decision-making, as well as the additional time spent on system use were examined. RESULTS: Subjects attempted to access the diagnostic aid on 595 occasions during the study period (8.6% of all medical assessments); subjects examined diagnostic advice only in 177 episodes (30%). Senior House Officers at hospitals with greater number of available computer workstations in the clinical area were most likely to consult the system, especially out of working hours. Diagnostic workups construed as 'unsafe' occurred in 47/104 cases (45.2%); this reduced to 32.7% following system consultation (McNemar test, p < 0.001). Subjects' mean 'unsafe' workups per case decreased from 0.49 to 0.32 (p < 0.001). System advice prompted the clinician to consider the 'correct' diagnosis (established at discharge) during initial assessment in 3/104 patients. Median usage time was 1 min 38 sec (IQR 50 sec-3 min 21 sec). Despite a modest increase in the number of diagnostic possibilities entertained by the clinician, no adverse effects were demonstrable on patient management following system use. Numerous technical barriers prevented subjects from accessing the diagnostic aid in the majority of eligible patients in whom they sought diagnostic assistance. CONCLUSION: We have shown that junior doctors used a Web-based diagnostic reminder system during acute paediatric assessments to significantly improve the quality of their diagnostic workup and reduce diagnostic omission errors. These benefits were achieved without any adverse effects on patient management following a quick consultation.