Surveillance of cerebral palsy in Norway; a national registry-based study

Abstract

Well-established cerebral palsy (CP) registries provide a solid framework to monitor, study and report on CP over time. This includes its causes, diagnosis, clinical manifestations and treatments/interventions. This thesis is a national registry-based study of individuals with CP born 1996 to 2010 and recorded in the Cerebral Palsy Registry of Norway (CPRN) and the Norwegian Patient Registry (NPR). Data from both registries were used to ensure that the studies were population-based. This was performed by linking the CPRN to the NPR, and validating all CP diagnosis codes recorded in the NPR, but not in the CPRN. Article I describes the results of the validation study, and the implications a complete and correct population can have on the calculation of prevalence estimates. The accurate prevalence of CP for individuals born in Norway during this study period is 2.4 per 1000 live births. Article II continued with a more in-depth investigation of the trends in prevalence and severity of CP, using clinical data from the CPRN and supplemented with data from the NPR. We found a significant decline in the prevalence of CP from 2.6 per 1000 live births in 1999 to 1.9 in 2010. This was mostly attributed to a decrease in the more severe bilateral spastic CP subtype (characterized by muscular stiffness on both sides of the body). We also found a decrease in the proportion of individuals with CP and severe motor impairments, epilepsy, intellectual disability and reduced speech. This is the first time a reduction in the prevalence and severity of CP has been reported in Norway. The decline was most likely due to improvements in antenatal, obstetric and neonatal care that have been introduced nationwide throughout the past few decades. To support these findings, we also explored the status of perinatal health for all children born in Norway during this study period, using summary statistics from the Medical Birth Registry of Norway Statistics Bank. There, we found a decline in the prevalence of children born preterm, mothers with preeclampsia during pregnancy and with multiples, all of which are well-known risk factors for CP. In addition, there was also a decline in perinatal mortality. Nonetheless, in article III we found that individuals who did receive a diagnosis of CP during this study period have a considerably higher burden of disease when compared with their peers in the general population without CP. Nearly all individuals with CP were recorded in the NPR with one or more disorders in addition to their CP condition (comorbidities), whether mild-to-severe or transient-to-chronic. When compared with the risks in the general population, individuals with CP had an excess risk for multiple medical, neurological and mental/behavioral disorders. As expected, many of the comorbidities were associated with the injury to the developing brain that caused CP (cocausal) or complications of the main CP condition. However, we also found that many comorbidities were also not intuitively related to CP. This thesis demonstrates the importance of continual surveillance of the CP population in Norway. By monitoring fluctuations in the prevalence and clinical manifestations of CP over time, we can provide up-to-date information to healthcare professionals and support their work in preventing or minimizing the impact of CP.