We do not have data on this for the country, neither for smaller areas. According to our previous study conducted in one city (São José dos Campos, in São Paulo state), we found that rates of under diagnosis were lower in the rich areas of the city (Nakamura et al., 2015).

References:

Nakamura, A., Opaleye, D., Tani, G., & Ferri, C. P. (2015). Dementia underdiagnosis in Brazil. The Lancet, 385(9966), 418–419. https://doi.org/10.1016/S0140-6736(15)60153-2