Advances in biomarker discovery for canine cognitive dysfunction: a comprehensive structured narrative review and future perspectives.

Canine Cognitive Dysfunction (CCD) is a naturally occurring neurodegenerative syndrome in aging dogs that shares clinical and neuropathological parallels with Alzheimer's disease (AD). As the demand for objective diagnostic tools grows, identifying reliable biofluid biomarkers is essential for clinical staging and therapeutic monitoring. This review synthesizes evidence on cerebrospinal fluid (CSF) and blood-based biomarkers (BBM) of CCD, focusing on amyloid-β (Aβ), neurofilament light chain (NfL), tau, and glial fibrillary acidic protein (GFAP). Evidence shows that Aβ42 and Aβ42/Aβ40 ratios exhibit stage-dependent, non-linear alterations resembling early compensatory phases in human AD. In contrast, tau pathology in CCD consists mainly of pre-tangle synaptic hyperphosphorylation rather than abundant neurofibrillary tangles, limiting its current diagnostic utility. GFAP, a marker of astroglial activation, shows inconsistent associations with cognitive decline and remains exploratory. Conversely, NfL has emerged as the most robust biomarker; CSF and plasma NfL levels consistently increase with age, correlate with cognitive impairment, and reflect central axonal pathology, making it the leading candidate for staging and monitoring disease progression. Overall, the CCD biomarker landscape supports a multimodal approach integrating Aβ dysregulation, axonal injury, and glial activation. Advancing this field requires harmonized diagnostic criteria, standardized sampling, and longitudinal studies. Such efforts will strengthen the translational value of CCD as a model for human dementia, accelerating discovery and therapeutic development across species.