MAPT and Alzheimer disease: Furthermore, 11 of 33 patients with SCD, where AD was suspected as an underlying cause before PET (33%), had a positive tau PET scan; 122 of 179 patients with MCI, where AD was suspected as underlying cause before PET (68%), had a positive tau PET scan; and 171 of 196 patients with dementia, where AD was suspected as underlying cause before PET (87%), had a positive tau PET scan.