Abstract
OBJECTIVE:
To explore the neuropsychological effects and levels of tau protein (TAU), amyloid β 1-42 (Aβ 1-42), and lipid peroxidase after 10 sessions of anodal transcranial direct current stimulation (tDCS) in patients with mild to moderate Alzheimer disease (AD).

PATIENTS AND METHODS:
A total of 46 consecutive patients with probable AD participated in this study. They were classified randomly into 2 equal groups: active versus sham. Each patient received 10 sessions of anodal tDCS over the left and right temporoparietal region for 20 minutes for each side with the cathode on the left arm. Patients were assessed using the Modified Mini Mental State Examination (MMMSE), clock drawing test, Montreal Cognitive Scale (MoCA), and the Cornell Scale for depression. Serum TAU, Aβ 1-42, and lipid peroxidase were measured before and after the 10th session.

RESULTS:
There was a significant improvement in the total score of each cognitive rating scale (MMMSE, clock drawing test, and MoCA) in the real group, whereas no such change was observed in the sham group. The Cornell depression score improved significantly in both groups. There was a significant increase in serum Aβ 1-42 ( P = .02) in the real but not in the sham group, with a significant Treatment condition × Time interaction ( P = .009). There was no significant effect on tau or lipid peroxidase in either group but a significant positive correlation between changes of Aβ1-42 and MMMSE ( P = .005) and MoCA ( P = .02).

CONCLUSION:
The observed cognitive improvements were complemented by parallel changes in serum levels of Aβ 1-42.

TRIAL REGISTRATION:
ClinicalTrials.gov NCT03313518.