There is an urgent need for clinical blood biomarkers which can rule in/out neurological disorders early in those with psychiatric symptoms, personality or behavioural changes and/or functional decline together with cognitive symptoms. The neuronal axonal protein neurofilament light (NfL) is released from damaged neuronal axons and can be measured in in blood and cerebrospinal fluid (CSF). We have undertaken a series of studies aimed at examining the clinical utility of blood and CSF NfL in assisting with the distinction between psychiatric and neurodegenerative / neurological disorders.

Since 2016 we have measured blood and CSF NfL levels across multiple psychiatric and neurological populations recruited through Neuropsychiatry, Royal Melbourne Hospital and our collaborators (national and international). We have described our findings in a series of published studies. Data from our ongoing work, in larger cohorts and diagnostic groups, will be presented. The diagnostic groups include people with psychiatric disorders (schizophrenia, bipolar disorder, depression, functional neurological disorders), neurodegenerative disorders (Alzheimer’s disease, frontotemporal dementia, Huntington’s disease, Niemann-Pick Type C) and neurological disorders (e.g., epilepsy).

Our initial pilot study (n=129) found that CSF NfL was a promising biomarker in differentiating psychiatric from neurological disorders. In our larger follow up larger study (n=498) which included more diagnostic groups CSF NfL levels exhibited high accuracy (91%), sensitivity (92%), and specificity (87%) in differentiating psychiatric from neurological disorders, and distinguished behavioural variant frontotemporal dementia from frontal lobe syndrome phenocopies/mimics, with high accuracy. We have found that NfL is not elevated in people with treatment resistant schizophrenia compared to controls and is elevated in people with Niemann-Pick Type C compared to people with psychiatric disorders and controls. Further (unpublished) data has shown that these findings are replicated with plasma NfL levels across 400 further psychiatric, neurological and control participants.

NfL is a highly promising biomarker which differentiates psychiatric from neurological disorders with high sensitivity and specificity. The translation of NfL levels into standard clinical practice could substantially improve the clinical diagnostic process in people with complex neuropsychiatric and cognitive disorders.