Post-hoc analysis showed a significant effect for p-tau on axonal length density in the DLB group (β =  − 5.04 × 10–5; t(24.2) =  − 3.24, P = 0.003) compared to PD (β =  − 1.5 × 10–5; t(40.6) =  − 0.42, P = 0.67) and PDD (β =  − 6.4 × 10–5; t(41.3) =  − 0.7, P = 0.5) as well as for the agranular compared to dysgranular insula (β =  − 5 × 10–5; t(42.3) =  − 3, P = 0.004). Here, MAPT is linked to Lewy body dementia.