Geographic Variation in Diagnostic Codes Associated With Mild Cognitive Impairment, Alzheimer Disease, and Related Dementias.

Background

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Objectives

Mild cognitive impairment (MCI), Alzheimer disease (AD), and AD-related dementias (ADRD) are growing public health concerns. Regional, demographic, and clinical differences in these diagnoses and associated comorbid conditions may inform strategies to improve prevention, care, and outcomes. To assess the demographic and geographic distribution of patients in the United States with coded MCI or AD/ADRD, the prevalence of common comorbidities, and the frequency and timing of progression to complicated MCI or AD/ADRD within 180 days, using data from the American Academy of Neurology's former Axon Registry.

Methods

This observational study included adults aged 50-89 years with at least 1 outpatient encounter between 2017 and 2023 in 201 participating US neurology practices. Registry data were linked to the Centers for Disease Control and Prevention's 2019 Social Determinants of Health data set to assign patients to geographic regions. ICD-10 codes were used to identify MCI and AD/ADRD diagnoses, define comorbid conditions, and classify "complicated" MCI or AD/ADRD (e.g., with behavioral disturbances). The primary outcomes were odds of coded MCI/AD/ADRD, prevalence of top comorbidities, and proportion of patients progressing to complicated MCI/AD/ADRD within 180 days of initial diagnosis, stratified by region.

Results

Of 1,144,081 individuals with at least 1 documented outpatient encounter, 146,273 (12.8%) had MCI or AD/ADRD ICD codes. Of those, 65,088 (44.5%) were in the South, 35,027 (23.9%) in the Midwest, 30,008 (20.5%) in the Northeast, and 16,134 (11.0%) in the West. Unadjusted odds of MCI/AD/ADRD codes were 0.170 (Northeast), 0.155 (South), 0.134 (West), and 0.125 (Midwest). Among those with uncomplicated MCI or AD/ADRD at first encounter, the highest proportion of progression to complicated codes within 180 days was in the Northeast (2.04%), followed by the West (1.91%), South (1.24%), and Midwest (1.06%). Common comorbidities included hypertension, depression or mood disorders, and gait abnormalities.

Discussion

These findings highlight geographic and demographic variations in coded MCI/AD/ADRD prevalence and progression. Future studies should address underlying factors and the impact of comorbidities on outcomes, ultimately guiding more targeted approaches to dementia prevention and management. Future studies that phenotype AD/ADRD beyond the use of ICD codes can further validate the results.