Plasma amyloid‐β40/42 ratio can distinguish co‐morbid Alzheimer’s disease pathology in patients with Lewy body disease

Abstract Background Although comorbidity with Alzheimer’s disease (AD) is not uncommon in Lewy body disease (LBD), no blood biomarkers which can identify AD pathology in LBD have ever been established. Objectives To investigate if plasma amyloid‐β (Aβ) biomarkers can distinguish AD comorbidity in LBD patients. Methods We examined plasma Aβ 40 , and Aβ 42 in 15 patients with Aβ negative LBD, 10 with Aβ positive LBD, and 37 with AD. In addition, patients underwent amyloid‐positron emission tomography imaging ( 11 C Pittsburgh compound‐B) or cerebrospinal fluid Aβ 42 test. Results The plasma Aβ 40 /Aβ 42 ratio was significantly decreased in patients with Aβ+ LBD compared with those with Aβ‐ LBD (p = 0.037) and could accurately classify the two diseases (area under the curve, 0.727). Conclusions Plasma Aβ 40 /Aβ 42 ratio might be a useful marker for comorbid AD pathology in LBD.