Dementia Identification with EMR

The major data sources for identification of dementia cases in the UK comprise EMRhospitalisationdata, death records and dispensed prescribing records. From thesesources, we categoriseany dementia into the following clinicopathological subtypes:Alzheimer's dementia,Vascular dementia, Other dementia (any dementia type otherthan Alzheimer's or Vascular),Unspecified dementia (where a specific sub-type isnot recorded) and Possible dementia(where the diagnosis is not clear for it to definitivelybe dementia). For individualswith dementia, the earliest date of mention of dementia(in any of the sources) istaken as a surrogate for the incident date of dementia.

For more information about the phenotype, please refer to linked publications.

We use a combination of ICD-10 codes (for hospitalisation and death records) andBNFcodes (prescribing records) to adjudicate dementia sub-type as listed in theconceptlist below. With regards to prescriptions, given that in the UK, medicationsfor dementia(donepezil hydrochloride, galantamine, rivastigmine, and memantine hydrochloride)arelargely indicated for individuals with Alzheimer dementia, a history of redeemingaprescription for one of these drugs can be considered indicative of a diagnosisofAlzheimer's.

Given the longitudinal nature of our records, we make use of the entire patient historytodetermine a distribution over dementia sub-types (if any). Specifically, we summariseeachpatient's coding episode into a binary indication of whether each dementia subtype(Alzheimer's,Vascular, Other, Unspecified or Possible) is mentioned or not. Foreach patient, wethen count the number of coding episodes for each subtype and divideit by the totalnumber of coding episodes over all subtypes, to yield a proportion(probability) overdementia subtypes for that patient - if the patient has no evidenceof dementia, thenthis proportion is taken to be all 0s. Subsequently, for dementiasubjects, the earliestdate of mention of dementia (in any of the sources) is takenas a surrogate for theincident date of dementia, while the last date on record fora non-dementia patientis taken to be the last date of follow-up for that subject.

For more detail on implementation, please refer to linked publications.