Dysregulated neurofluid coupling as a new noninvasive biomarker for primary progressive aphasia.

Accumulation of pathological tau is one of the primary causes of Primary Progressive Aphasia (PPA). The glymphatic system is crucial for removing metabolite waste from the brain whereas impairments in glymphatic clearance in PPA are poorly understood. Thus, this study aims to investigate the role of dysregulated macroscopic cerebrospinal fluid (CSF) movement in PPA. Fifty-six PPA individuals and ninety-four healthy controls were included in our analysis after excluding those with excessive head motions during the scan. The coupling strength between blood-oxygen-level-dependent (BOLD) signals in the gray matter and CSF flow was calculated using Pearson correlation and compared between the groups. Its associations with clinical characteristics including scores from Clinical Dementia Rating (CDR), Mini-Mental State Exam, Geriatric Depression Scale and with morphological measures in the hippocampus and entorhinal cortex were examined. PPA subjects exhibited weaker global BOLD-CSF coupling compared to HCs, indicating impairments in glymphatic function in the patients (p = 0.01). In the PPA but not HC group, global BOLD-CSF coupling correlated with the CDR scores (p = 0.04) and hippocampal volume (p = 0.009). The observed decoupling between global brain activity and CSF flow and its association with symptomatology and brain structural changes in PPA converges with previous reports on the same measure in other neurodegenerative diseases. These findings support the potential role of global BOLD-CSF coupling as a noninvasive marker for glymphatic dysregulation in PPA.