TSPO and Alzheimer disease: While several studies using the first-generation radioligand [11C]PK 11195 reported higher TSPO PET brain signal in amyotrophic lateral sclerosis, AD, PD, and in brains of people at risk of Huntington’s disease when compared to controls [31,32,85,86,87,88,89,90], other studies using second-generation ligands reported no difference in TSPO PET signal in AD and multiple sclerosis [45,91,92,93,94].