Reduced brain amyloid burden in elderly patients with narcolepsy type 1

Objective: To determine whether brain amyloid burden in elderly patients with narcolepsy type 1 (NT1) is lower than in controls, and to assess in patients with NT1 the relationships between amyloid burden, cerebral spinal fluid (CSF) markers of Alzheimer disease (AD), CSF orexin-A, and cognitive profile.

Methods: Cognitive and ¹⁸ F-florbetapir positron emission tomography (PET) data were compared in patients with NT1 aged ≥ 65 years (n = 23) and in age- and sex-matched controls free of clinical dementia selected from the Alzheimer's Disease Neuroimaging Initiative (ADNI; n = 69) and the Multi-Domain Intervention Alzheimer's Prevention Trial (MAPT-18F AV45-PET; n = 23) cohorts. The standardized uptake values (SUVs) of the cortical retention index for 6 regions of interest were computed and averaged to create a mean SUV ratio normalized to 3 subcortical reference regions (cerebellum, pons, and a composite region). A cortical/cerebellum SUV ratio ≥ 1.17 defined positive PET amyloid.

Results: Lower cortical amyloid burden was observed in the NT1 than in the ADNI and MAPT-AV45 groups (mean cortical/cerebellum SUV ratios = 0.95 ± 0.15, 1.11 ± 0.18 [p < 0.0001], and 1.14 ± 0.17 [p = 0.0005], respectively). Similar results were obtained with all subcortical reference regions and for all cortical regions of interest, except cingulum. Only 1 patient with NT1 (4.4%) had positive PET amyloid compared with 27.5% in the ADNI and 30.4% in the MAPT-AV45 group. In the NT1 group, cortical or regional amyloid load was not associated with CSF orexin-A, CSF AD biomarkers, or neuropsychological profile.

Interpretation: Lower brain amyloid burden, assessed by ¹⁸ F-florbetapir PET, in patients with NT1 suggests delayed appearance of amyloid plaques. ANN NEUROL 2019;85:74-83.