title: Dementia risk after traumatic brain injury vs nonbrain trauma: the role of age and severity.
abstract: OBJECTIVE
  Epidemiologic evidence regarding the importance of traumatic brain injury (TBI) as a risk factor for dementia is conflicting. Few previous studies have used patients with non-TBI trauma (NTT) as controls to investigate the influence of age and TBI severity.
  
  
  OBJECTIVE
  To quantify the risk of dementia among adults with recent TBI compared with adults with NTT.
  
  
  METHODS
  This retrospective cohort study was performed from January 1, 2005, through December 31, 2011 (follow-up, 5-7 years). All patients 55 years or older diagnosed as having TBI or NTT in 2005 and 2006 and who did not have baseline dementia or die during hospitalization (n = 164,661) were identified in a California statewide administrative health database of emergency department (ED) and inpatient visits.
  
  
  METHODS
  Mild vs moderate to severe TBI diagnosed by Centers for Disease Control and Prevention criteria using International Classification of Diseases, Ninth Revision (ICD-9)codes, and NTT, defined as fractures excluding fractures of the head and neck, diagnosed using ICD-9 codes.
  
  
  METHODS
  Incident ED or inpatient diagnosis of dementia (using ICD-9 codes) 1 year or more after initial TBI or NTT. The association between TBI and risk of dementia was estimated using Cox proportional hazards models before and after adjusting for common dementia predictors and potential confounders. We also stratified by TBI severity and age category (55-64, 65-74, 75-84, and ≥85 years).
  
  
  RESULTS
  A total of 51,799 patients with trauma (31.5%) had TBI. Of these, 4361 (8.4%) developed dementia compared with 6610 patients with NTT (5.9%) (P < .001). We found that TBI was associated with increased dementia risk (hazard ratio [HR], 1.46; 95% CI, 1.41-1.52; P < .001). Adjustment for covariates had little effect except adjustment for age category (fully adjusted model HR, 1.26; 95% CI, 1.21-1.32; P < .001). In stratified adjusted analyses, moderate to severe TBI was associated with increased risk of dementia across all ages (age 55-64: HR, 1.72; 95% CI, 1.40-2.10; P < .001; vs age 65-74: HR, 1.46; 95% CI, 1.30-1.64; P < .001), whereas mild TBI may be a more important risk factor with increasing age (age 55-64: HR, 1.11; 95% CI, 0.80-1.53; P = .55; vs age 65-74: HR, 1.25; 95% CI, 1.04-1.51; P = .02; age interaction P < .001).
  
  
  CONCLUSIONS
  Among patients evaluated in the ED or inpatient settings, those with moderate to severe TBI at 55 years or older or mild TBI at 65 years or older had an increased risk of developing dementia. Younger adults may be more resilient to the effects of recent mild TBI than older adults.
authors.affiliation: Memory and Aging Center, Department of Neurology, University of California, San Francisco2Department of Veterans Affairs, San Francisco Veterans Affairs Medical Center, San Francisco, California.
authors.forename: Raquel C
authors.initials: RC
authors.lastname: Gardner
authors.affiliation: Department of Neurology, University of Michigan, Ann Arbor4Department of Veterans Affairs, Veterans Affairs Center for Clinical Management and Research, Ann Arbor Veterans Affairs Healthcare System, Ann Arbor, Michigan.
authors.forename: James F
authors.initials: JF
authors.lastname: Burke
authors.affiliation: Department of Veterans Affairs, San Francisco Veterans Affairs Medical Center, San Francisco, California5Department of Epidemiology and Biostatistics, University of California, San Francisco.
authors.forename: Jasmine
authors.initials: J
authors.lastname: Nettiksimmons
authors.affiliation: Department of Veterans Affairs, San Francisco Veterans Affairs Medical Center, San Francisco, California6Department of Psychiatry, University of California, San Francisco.
authors.forename: Allison
authors.initials: A
authors.lastname: Kaup
authors.affiliation: Department of Veterans Affairs, San Francisco Veterans Affairs Medical Center, San Francisco, California5Department of Epidemiology and Biostatistics, University of California, San Francisco6Department of Psychiatry, University of California, San Francisc.
authors.forename: Deborah E
authors.initials: DE
authors.lastname: Barnes
authors.affiliation: Memory and Aging Center, Department of Neurology, University of California, San Francisco2Department of Veterans Affairs, San Francisco Veterans Affairs Medical Center, San Francisco, California5Department of Epidemiology and Biostatistics, University of.
authors.forename: Kristine
authors.initials: K
authors.lastname: Yaffe
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001930:Brain Injuries / Q000150:complications / Q000453:epidemiology*; D002140:California / Q000453:epidemiology; D003704:Dementia / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D005500:Follow-Up Studies; D050723:Fractures, Bone / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012306:Risk; D015599:Trauma Severity Indices