Dementia diagnosis and prevalence in the Lothian Birth Cohort 1936 using medical data linkage

Background The Lothian Birth Cohort 1936 (LBC1936) is a longitudinal study of ageing with well-characterised assessments, but until now, it has relied on self-report or proxies for dementia outcomes. This report describes a framework for clinical dementia ascertainment and its implementation. We report the prevalence of all-cause dementia and dementia subtypes in 865 individuals aged 70 years and older from the LBC1936. Methods Electronic Health Records (EHR) of all participants were reviewed, and relevant information was extracted to form case vignettes for everyone with any record of cognitive dysfunction. The EHR data sources include hospital and clinic letters, general practitioner and hospital referrals, prescribed medications, imaging and laboratory results. Death certificate data were obtained separately. Clinician assessments were performed when there was concern about a participant’s cognition. A diagnosis of probable dementia, possible dementia, or no dementia was agreed upon by a consensus diagnostic review board, comprised of a multidisciplinary team of clinical dementia experts who reviewed case vignettes and clinician assessment letters. For those with probable dementia, a subtype was also determined, where possible. Finally, we compared the agreement between our newly ascertained dementia outcomes with the existing self-reported dementia outcomes. Results The EHR review identified 163 out of 865 (18.8%) individuals as having cognitive dysfunction. At the consensus diagnostic review board, 118/163 were diagnosed with probable all-cause dementia, a prevalence of 13.6%. Age-specific dementia prevalence increased with age from 0.8% (65-74.9 years) to 9.93% (85-89.9 years). Prevalence rates for women were higher in nearly all age groups. The most common subtype was dementia due to Alzheimer disease (49.2%), followed by mixed Alzheimer and cerebrovascular disease (17.0%), dementia of unknown or unspecified cause (16.1%), and dementia due to vascular disease (8.5%). Self-reported dementia outcomes were positive in only 17.8% of ascertained dementia outcomes. Conclusions Dementia outcomes have been clinically ascertained in the LBC1936 using a robust systematic approach that closely aligns with diagnosing dementia in practice. This provides useful detailed outcomes for further analyses of LBC1936 to allow exploration of lifecourse predictors of dementia. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The present manuscript received no direct funding. All researchers are independent of their funders. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All data are available on reasonable request here: I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data are available on reasonable request here: * CFAS : Cognitive Function and Ageing Studies CI : Confidence Interval CT : Computerised Tomography DSM-5 : Diagnostic and Statistical Manual of Mental Disorders - Fifth Edition DaT : Dopamine Transporter EHR : Electronic Health Records ELSA : English Longitudinal Study of Ageing FTD : Frontotemporal Dementia ICD-11 : International Classification of Diseases-11 LBC1936 : Lothian Birth Cohort 1936 MRI : Magnetic Resonance Imaging MMSE : Mini-Mental State Exam NHS : National Health Service SPECT : Single-Photon Emission Computerised Tomography SD : Standard Deviation