Dementia Identification with EMR

The major data sources for identification of dementia cases in the UK comprise EMRhospitalisation data, death records and dispensed prescribing records. From thesesources, we categorise any 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 individuals with dementia, the earliest date of mention of dementia(in any of the sources) is taken 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) andBNF codes (prescribing records) to adjudicate dementia sub-type as listed in theconcept list below. With regards to prescriptions, given that in the UK, medicationsfor dementia (donepezil hydrochloride, galantamine, rivastigmine, and memantine hydrochloride)are largely indicated for individuals with Alzheimer dementia, a history of redeeminga prescription for one of these drugs can be considered indicative of a diagnosisof Alzheimer's.

Given the longitudinal nature of our records, we make use of the entire patient historyto determine a distribution over dementia sub-types (if any). Specifically, we summariseeach patient'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, we then count the number of coding episodes for each subtype and divideit by the total number of coding episodes over all subtypes, to yield a proportion(probability) over dementia subtypes for that patient - if the patient has no evidenceof dementia, then this proportion is taken to be all 0s. Subsequently, for dementiasubjects, the earliest date of mention of dementia (in any of the sources) is takenas a surrogate for the incident date of dementia, while the last date on record fora non-dementia patient is taken to be the last date of follow-up for that subject.

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