The value of the Evans and bicaudate indices for predicting poor cognitive performance and central atrophy. Results from the Atahualpa Project

Recent studies suggested that both the Evans index (EI) and the bicaudate index (BI) are predictive markers of central atrophy and, as such, have been inversely associated with cognitive performance. This study investigated whether the EI and the BI (independently and combined) correlated with the MoCA score by means of generalized linear models adjusted for relevant confounders. Using a population-based design, 618 Atahualpa residents aged ≥40 underwent a head CT and MoCA testing. Both, the EI and the BI, were independently calculated by two readers, and a mean of the two values for each index was calculated for analysis. Generalized linear models showed inverse significant relationships between the EI and the BI with the MoCA score (p = 0.034, and p < 0.001, respectively). When both predictive variables (EI and BI) were included in a generalized linear model adjusted for all confounders, the BI remained significantly associated with the MoCA score (p = 0.004) but the EI did not (p = 0.677). This study shows that only the BI has and explanatory power outside the endogenous construct (central atrophy) for which both, the BI and the EI are part and parcel of.