Intracranial volume and dementia: some evidence in support of the cerebral reserve hypothesis

The brain reserve hypothesis has been posited as being one important mediating factor for developing dementia, especially Alzheimer's disease (AD). Evidence for this hypothesis is mixed though different methodologies have made these findings difficult to interpret. We examined imaging data from a large cohort (N=194) of mixed dementia patients and controls, 65years old and older from the Cache County, Utah Study of Memory and Aging for evidence of the brain reserve hypothesis using total intracranial volume (TICV) as a quantitative measure of pre-morbid brain size and a vicarious indicator of reserve. A broader spectrum of non-demented elderly control subjects from previous studies was also included for comparison (N=423). In addition, non-parametric Classification and Regression Tree (CART) analyses were performed to model group heterogeneity and identify any subgroups of patients where TICV might be an important predictor of dementia. Parametrically, no main effect was found for TICV when predicting a dementia diagnosis; however, the CART analysis did reveal important TICV subgroups, including a sex differential wherein ε4 APOE allele presence in males and low TICV predicted AD classification. TICV, APOE, and other potential mediator/moderator variables are discussed in the context of the brain reserve hypothesis.

Comparison of Lumin LED fluorescent attachment, fluorescent microscopy and Ziehl-Neelsen for AFB diagnosis

DESIGN

Cross-sectional studies in Russia (n = 502) and Macedonia (n = 205), with fluorochrome-stained sputum examined by 1) the new Lumin light emitting diode (LED) fluorescent attachment on a light microscope, and 2) conventional fluorescent microscope (CFM) available in each laboratory, and compared to 3) Ziehl-Neelsen (ZN) restaining/reading of the same smears. Poor readings of ZN-restained smears in Russia stimulated a retrospective laboratory registry analysis for sensitivity and specificity of directly ZN-stained smears (n = 791) from a previous period.

RESULTS

In Macedonia, the sensitivity of the Lumin and CFM were 87.8%, and that of restained ZN smears with conventional light microscope was 78.0%. In Russia, sensitivity was as follows: Lumin 72.8%, CFM 52.5%; re-stained ZN smears 28.5% and directly ZN stained smears 55.6%.

CONCLUSION

Fluorescence microscopy is more sensitive than conventional microscopy. The Lumin attachment to conventional light microscopes provided results equal to or better than the CFMs. Smear restaining for ZN showed a 12% advantage for Lumin and CFM in Macedonia, in line with other meta-analyses. Restaining for ZN gave poor results in Russia for unknown reasons. Retrospective analysis of directly ZN-stained smears showed 55.6% sensitivity compared to the Lumin (72.8%), which is also in line with the superiority of fluorescent microscopy reported in literature.