AIM To assess completeness and correctness of cerebral palsy (CP) diagnoses in the CerebralPalsy Register of Norway (CPRN) and the Norwegian Patient Register (NPR), and to estimate CP prevalence.METHOD Among 747 883 Norwegian residents born from 1996 to 2007, 2231 had a diagnosis of CP in the NPR while 1441 were registered in the CPRN. Children registered in the CPRN were considered to have a valid CP diagnosis. For those with a diagnosis of CP only in the NPR, two paediatricians reviewed the hospital records. The prevalence rate of CP with 95% confidence intervals (CI) was calculated on the basis of the combined data sets.RESULTS One thousand three hundred and ninety-eight children were registered with a diagnosis of CP in both registers, 43 children were only registered in the CPRN, and 824 only in the NPR. The review of hospital records revealed that 464 (59.5%) had CP. Thus, the NPR was 98% complete, and for 86% the diagnosis was correct. The completeness of the CPRN was 76%, while the diagnosis was considered correct for all children (100%). The resulting prevalence of CP was 2.5 (95% CI 2.4-2.7) per 1000.INTERPRETATION To gain accurate estimates of prevalence rates of CP, it is essential to combine data sources and to validate register data.The birth prevalence of cerebral palsy (CP) is considered to be a potential indicator of the quality of perinatal care, 1,2 while population-based prevalence rates provide important information for health care providers and society. In recently published Norwegian studies, the prevalence of CP has varied significantly.3-5 A study using information from the Norwegian Social Insurance Scheme reported a birth prevalence of 1.8 per 1000 among individuals born from 1967 to 2002.3 Sur en et al. found a population-based prevalence of 3.0 per 1000 Norwegian residents born from 1999 to 2010, using information extracted from the Norwegian Patient Register (NPR). 4The NPR is a compulsory national administrative health register, established in 1997. The NPR includes personidentifiable data from 2008 onwards. It contains structured data on all patients treated by the national specialist health services, including individual-level demographic, administrative, and clinical data. 6 In a third study, using information collected by the Cerebral Palsy Register of Norway (CPRN), Andersen et al. found the birth prevalence of CP to be 2.1 per 1000 for children born from 1996 to 1998. 5The CPRN is a consent-based national medical quality register established in 2006. This register contains clinical data on individual children born from 1996 onwards.Dedicated specialists from each of the 21 habilitation centres record data at three points in time: at diagnosis, and at ages 5 and 15 to 17 years. A paediatrician/paediatric neurologist is responsible for determining the CP diagnosis using the 'Decision tree for cerebral palsy' and 'Classification tree of CP subtypes' guidelines developed by the Surveillance of Cerebral Palsy in Europe (SCPE). 7 The age recommended for confirmation of the diagnosi...

NPR Norwegian Patient RegistryAIM To describe the total burden of disease in individuals with cerebral palsy (CP) in Norway.METHOD A comprehensive set of disorder categories were extracted from the Norwegian Patient Registry using International Statistical Classification of Diseases, 10th Revision diagnosis codes for individuals born between 1996 and 2010 who received specialist healthcare between 2008 and 2017 (0-21y). Individuals with CP were identified through a validation study in cooperation with the Cerebral Palsy Registry of Norway. Risk differences (proportions of individuals recorded with each disorder) were used to compare individuals with CP with the general population without CP. RESULTSThe study included 966 760 individuals. Among these, 2302 (0.24%) had CP (1330 males, 972 females). Of the individuals with CP, 95.0% were recorded with one or more comorbidity, and the risks of medical, neurological, and mental/behavioural disorders were higher compared with the risks in the general population. The most common neurological and mental/behavioural disorders were cocausal, i.e. attributed to the same injury to the developing brain that caused CP, while medical disorders were most often complications of CP or coincidentally co-occurring with CP.INTERPRETATION Individuals with CP have a considerably higher burden of medical, neurological, and mental/behavioural disorders compared with the general population, including disorders that are not directly caused by, or complications to, the brain injury. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. -5 0 5 10 15 20 25 30 35 40 45 Percentage of risk differences (99% CIs) Disorder category Risk difference (99% CI) Figure 1: Risk differences with 99% confidence intervals (CIs) comparing the occurrence of disorders between individuals with cerebral palsy and the general population born from 1996 to 2010. CNS, central nervous system; ADHD, attention-deficit/hyperactivity disorder. [Colour figure can be viewed at wileyonlinelibrary.com] Comorbidities in CP Sandra Julsen Hollung et al. 101

ObjectiveTo construct an updated comorbidity index (Patient Register Index [PRI]) using national data collections from Norway and compare its predictive ability of 1-year mortality with the Charlson Comorbidity Index (CCI).Materials and methodsData regarding over 1.11 million patients registered in the Norwegian Patient Register in 2010 and 2011 were used to construct the PRI. The PRI was evaluated by comparing its model fit and discrimination with the CCI.ResultsCompared with the CCI, the PRI weights decreased for six, increased for four, and were unchanged for seven diseases. When the PRI was added to the model including age and sex, the age effects were reduced by up to 38% for patients older than 50 years. All measures of model fit improved for the PRI model.ConclusionAdjustment for comorbidity is especially important for patients 50 years of age or older, and its effect on 1-year mortality is almost comparable to the age effect. The PRI is based on more recent data than the CCI, and is more representative of the general population due to its construction.

Marianne Aardal Grytaas er overlege ved Seksjon for hormonsjukdommar og Register for organspesifikke autoimmune sykdommer (ROAS) ved Haukeland universitetssjukehus. Forfatteren har fylt ut ICMJE-skjemaet og oppgir ingen interessekonflikter. LARS BREIVIKLars Breivik er overingeniør ved Universitetet i Bergen og forskningssekretaer i Register for organspesifikke autoimmune sykdommer (ROAS) ved Haukeland universitetssjukehus. Forfatteren har fylt ut ICMJE-skjemaet og oppgir ingen interessekonflikter. ANDERS PALMSTRØM JØRGENSENAnders Palmstrøm Jørgensen er overlege ved Seksjon for spesialisert endokrinologi ved Oslo universitetssykehus (OUS), Rikshospitalet, og er ansatt som OUS-representant i Register for organspesifikke autoimmune sykdommer (ROAS). Forfatteren har fylt ut ICMJE-skjemaet og oppgir ingen interessekonflikter.