MAPT and Schnyder corneal dystrophy: It has been suggested that in case of cognitive impairment at the MCI or dementia level, the tau PET results might be used both to rule in and to rule out AD as the underlying primary pathology,23 but in cognitively unimpaired patients with SCD, the tau PET result might only be used to rule in AD pathology as the underlying cause.16,25,29,30 We recommend that tau PET is only used in patients with SCD when there is an increased risk of an underlying AD pathology and where the information may result in a beneficial change in patient management.