CBS and Alzheimer disease: For instance, patients with AD-CBS (predominant 3/4R) and 4R-CBS (predominant 4R) are characterized by involvement of the motor cortex and patients with typical AD (predominant 3/4R) and argyrophilic grain disease (predominant 4R) comprise tau accumulation in parietal-temporal cortices.34 Thus, detection of differences in [18F]PI-2620 binding characteristics among different tau isoforms would potentially facilitate a more reliable differential diagnosis.