Research from JAMA Neurology — Comparison of Visual and Quantitative Florbetapir F 18 Positron Emission Tomography Analysis in Predicting Mild Cognitive Impairment Outcomes

Cerebrospinal fluid (CSF) neurofilament light chain (NfL) has emerged as putative diagnostic biomarker in amyotrophic lateral sclerosis (ALS), but it remains a matter of debate, whether CSF total tau (ttau), tau phosphorylated at threonine 181 (ptau) and the ptau/ttau ratio could serve as diagnostic biomarker in ALS as well. Moreover, the relationship between CSF NfL and tau measures to further axonal and (neuro)degeneration markers still needs to be elucidated. Our analysis included 89 ALS patients [median (range) age 63 (33–83) years, 61% male, disease duration 10 (0.2–190) months] and 33 age- and sex-matched disease controls [60 (32–76), 49%]. NfL was higher and the ptau/ttau ratio was lower in ALS compared to controls [8343 (1795–35,945) pg/ml vs. 1193 (612–2616), H(1) = 70.8, p < 0.001; mean (SD) 0.17 (0.04) vs. 0.2 (0.03), F(1) = 14.3, p < 0.001], as well as in upper motor neuron dominant (UMND, n = 10) compared to classic (n = 46) or lower motor neuron dominant ALS [n = 31; for NfL: 16,076 (7447–35,945) vs. 8205 (2651–35,138) vs. 8057 (1795–34,951)], Z ≥ 2.5, p ≤ 0.01; for the ptau/ttau ratio: [0.13 (0.04) vs. 0.17 (0.04) vs. 0.18 (0.03), p ≤ 0.02]. In ALS, NfL and the ptau/ttau ratio were related to corticospinal tract (CST) fractional anisotropy (FA) and radial diffusivity (ROI-based approach and whole-brain voxelwise analysis). Factor analysis of mixed data revealed a co-variance pattern between NfL (factor load − 0.6), the ptau/ttau ratio (0.7), CST FA (0.8) and UMND ALS phenotype (− 2.8). NfL did not relate to any further neuroaxonal injury marker (brain volumes, precentral gyrus thickness, peripheral motor amplitudes, sonographic cross-sectional nerve area), but a lower ptau/ttau ratio was associated with whole-brain gray matter atrophy and widespread white matter integrity loss. Higher NfL baseline levels were associated with greater UMN disease burden, more rapid disease progression, a twofold to threefold greater hazard of death and shorter survival times. The findings that higher CSF NfL levels and a reduced ptau/ttau ratio are more associated with clinical UMN involvement and with reduced CST FA offer strong converging evidence that both are markers of central motor degeneration. Furthermore, NfL is a marker of poor prognosis, while a low ptau/ttau ratio indicates extramotor pathology in ALS.

Non-amyloid cerebral small vessel disease (CSVD) and cerebral amyloid angiopathy (CAA) may be interrelated through the damaged basement membranes (BMs) and extracellular matrix changes of small vessels, resulting in a failure of β-amyloid (Aβ) transport and degradation. We analyzed BM changes and the pattern of deposition of Aβ in the walls of blood vessels in spontaneously hypertensive stroke-prone rats (SHRSP), a non-transgenic CSVD model. In 45 SHRSP and 38 Wistar rats aged 18 to 32 weeks: (i) the percentage area immunostained for vascular collagen IV and laminin was quantified; (ii) the capillary BM thickness as well as endothelial and pericyte pathological changes were analysed using transmission electron microscopy (TEM); and (iii) the presence of vascular Aβ was assessed. Compared with controls, SHRSP exhibited a significantly higher percentage area immunostained with collagen IV in the striatum and thalamus. SHRSP also revealed an age-dependent increase of the capillary BM thickness and of endothelial vacuoles (caveolae) within subcortical regions. Endogenous Aβ deposits in the walls of small blood vessels were observed in the cortex (with the highest incidence found within fronto-parietal areas), striatum, thalamus and hippocampus. Vascular β-amyloid accumulations were frequently detected at sites of small vessel wall damage. Our data demonstrate changes in the expression of collagen IV and of the ultrastructure of BMs in the small vessels of SHRSP. Alterations are accompanied by vascular deposits of endogenous Aβ. Impaired β-amyloid clearance along perivascular and endothelial pathways and failure of extracellular Aβ degradation may be the key mechanisms connecting non-amyloid CSVD and CAA.

Deep perforator arteriopathy (DPA) and cerebral amyloid angiopathy (CAA) are the commonest known cerebral small vessel diseases (CSVD), which cause ischaemic stroke, intracebral haemorrhage (ICH) and vascular cognitive impairment (VCI). While thus far mainly considered as separate entities, we here propose that DPA and CAA share similarities, overlap and interact, so that ‘pure’ DPA or CAA are extremes along a continuum of age‐related small vessel pathologies. We suggest blood‐brain barrier (BBB) breakdown, endothelial damage and impaired perivascular β‐amyloid (Aβ) drainage are hallmark common mechanisms connecting DPA and CAA. We also suggest a need for new biomarkers (e.g. high‐resolution imaging) to deepen understanding of the complex relationships between DPA and CAA.