Frontal dysfunction blocks the therapeutic effect of THA on attention in Alzheimer's disease.

We evaluated the effect of a single dose of a cholinesterase inhibitor, tetrahydroaminoacridine (THA; 25 and 50 mg, orally), on attention in patients with Alzheimer's disease (AD). THA 50 mg improved performance in attentional measures (Trail Making Test, Big/Little Circle, Simple and Choice Reaction Time) in nine of 28 patients with AD. We analysed retention of 99mTc-labelled ethylene dicysteinate (ECD) in the cortical areas using single photon emission computed tomography. Those patients who benefited from THA treatment had bilaterally higher frontal and prefrontal ECD retention values. We suggest that THA may improve attention in patients with AD, but a severe frontal dysfunction may block the therapeutic effect of THA.