Stability of individual dementia diagnoses in routine care: Implications for epidemiological studies

PURPOSE: Epidemiological and health care research frequently rely on diagnoses from routine care, but the intra-individual stability of diagnoses of Alzheimer's disease (AD), vascular dementia (VD) or other forms of dementia (oD) in patients over time is understudied. More data on the diagnostic stability is needed to appraise epidemiological findings from such studies. METHODS: Using health claims data of the years 2004–2016 from the German Pharmacoepidemiological Research Database, 160 273 patients aged ≥50 with incident dementia were identified and followed for 4 years. According to the incident ICD-10 codes patients were assigned to the categories AD, VD or oD. Changes between categories during follow-up were calculated. RESULTS: Overall, 18.8% had incident AD (VD: 21.5%, oD: 59.7%). Fifteen thousand eight hundred forty-two patients had only one dementia diagnosis during 4 years (AD: 7.4%, VD: 12.4%, oD: 9.8%). Among those with more than one diagnosis, the incident diagnosis matched the last diagnosis in 65.1% (AD), 53.9% (VD) and 73.8% (oD) of patients. Changes in the diagnostic category were higher in patients with AD (mean: 5.1) than in patients with VD (3.6) or oD (3.3). Patients with stable AD diagnoses during the observation period were younger (median: 76 vs. 79 years) and had less inpatient treatment days (median: 14 days) than patients with changes from an AD diagnosis to another category or from another category to AD (27 days). CONCLUSIONS: While health claims data are feasible for estimating the incidence of dementia in general, the substantial number of changes in dementia diagnoses during the course of the disease warrant caution on the interpretation of epidemiological data on specific dementia types