Prevalence of Mild and Severe Cognitive Impairment in World Trade Center Exposed Fire Department of the City of New York (FDNY) and General Emergency Responders

Abstract

Background: The emergency personnel who responded to the World Trade Center (WTC) attacks endured severe occupational exposures, yet the prevalence of cognitive impairment remains unknown among WTC-exposed-FDNY-responders. The present study screened for mild and severe cognitive impairment in WTC-exposed FDNY responders using objective tests, compared prevalence rates to a cohort of non-FDNY WTC-exposed responders, and descriptively to meta-analytic estimates of MCI from global, community, and clinical populations.

Methods: A sample of WTC-exposed-FDNY responders (n = 343) was recruited to complete an extensive battery of cognitive, psychological, and physical tests. The prevalences of domain-specific impairments were estimated based on the results of norm-referenced tests, and the Montreal Cognitive Assessment (MoCA), Jak/Bondi criteria, Petersen criteria, and the National Institute on Aging and Alzheimer's Association (NIA-AA) criteria were used to diagnose MCI. NIA-AA criteria were also used to diagnose severe cognitive impairment. Generalized linear models were used to compare prevalence estimates of cognitive impairment to a large sample of WTC-exposed-non-FDNY responders from the General Responder Cohort (GRC; n = 7102) who completed the MoCA during a similar time frame.

Result: Among FDNY responders under 65 years, the unadjusted prevalence of MCI varied from 52.57% to 71.37% depending on the operational definition of MCI, apart from using a conservative cut-off applied to MoCA total scores (18 < MoCA < 23), which yielded a markedly lower crude prevalence (24.31%) compared to alternative criteria. The prevalence of MCI was higher among WTC-exposed-FDNY-responders, compared to WTC-exposed-non-FDNY-GRC-responders (adjusted RR = 1.53, 95% C.I. = [1.24, 1.88], p < .001) and meta-analytic estimates from different global, community, and clinical populations. Following NIA-AA diagnostic guidelines, 4.96% of WTC-exposed-FDNY-responders met the criteria for severe impairments (95% CI = [2.91% to 7.82%]), a prevalence that remained largely unchanged after excluding responders over the age of 65 years.

Discussion: There is a high prevalence of mild and severe cognitive impairment among WTC-responders highlighting the putative role of occupational/environmental and disaster-related exposures in the etiology of accelerated cognitive decline.

Figure 1.

Prevalence of Mild Cognitive Impairment in WTC Responders and from Meta-Analyses of Community and Clinical Populations Notes. Squares mark the number of estimated cases of MCI per 100 individuals at risk with horizontal lines denoting 95% confidence intervals.

Figure 2.

Comparing Distributions of Cognitive Impairment Measured by the MoCA in Two Cohorts of WTC Responders Notes. Level of cognitive impairment was measured using MoCA total scores, and MCI was determined using codebook criteria and conservative criteria. “0%” indicates less than 0.50%. To help ease interpretation of the statistics reported in panel C, the standardized mean difference between cohorts is 0.24, approximately 59.5% of responders from the general responder cohort have MoCA total scores above the mean of FDNY responders, 90.4% of scores from the two cohorts overlap, and there is a 56.7% chance that a WTC responder picked at random from the GRC will have better cognitive performance on the MoCA than a WTC responder picked at random from the FDNY cohort. Crude prevalence rates based on the depicted criteria are reported in Table 2.

Figure 3.

Domain-Specific Correlates of Mild-to-Severe Cognitive Impairment in WTC-Exposed FDNY Responders Notes. Colored shapes denote multiple regression coefficients for mild cognitive impairment (coded 0 = unimpaired, 1 = impaired) and domain-specific continuous measures of cognitive and physical function (reported on the x-axis) standardized with respect to the criterion (STDY) and adjusted for the effects of age. Vertical bars donote 95% confidence intervals calculated using heteroskedasticity-consistent standard errors. Coefficients with 95% confidence intervals that do not include zero (i.e., vertical bars that do not cross the dashed horizontal line) are statistically significant at p < .05. Scores for TMT-A and TMT-B were reserve coded so lower scores indicate worse performance.

Figure 4.

Severity of Domain-Specific Cognitive Impairments in WTC-Exposed FDNY Responders Notes. Prevalence rates of domain-specific impairments are plotted across levels of severity based on age-adjusted norms. Horizontal bars donote 95% confidence intervals calculated using the exact method.