Neuron-Specific Enolase as a Biomarker for Selected Neurological and Psychiatric Disorders—A Systematic Review of the Literature

<i>Background and Objectives</i>: Neuron-specific enolase (NSE) is an isoenzyme of enolase, of which the γ isoform is expressed in nerve cells. The activity of NSE occurs during late neuronal differentiation, which determines the specificity of the enzyme for neurodevelopmental cells. The activity of NSE is also observed in processes associated with neuronal damage. The aim of this study was to present the state of the art related to the knowledge, advances, and possible developmental directions in terms of the use of NSE as a biomarker in the diagnosis of selected neurological and mental disorders (NDs, MDs), with particular emphasis on ischemic stroke (IS) and psychotic disorders (PSDs). <i>Materials and Methods</i>: A literature review was performed using the PubMed, Embase, and Scopus databases. Keywords such as "neuron-specific enolase", "neuron-specific enolase in schizophrenia", "neuron-specific enolase in ischemic stroke", "neuron-specific enolase in psychiatric disorders", and "neuron-specific enolase in neurological diseases" were used during the literature search. A total of 11,350 items were found. However, 188 papers were finally selected after applying the filters ("clinical trial", "meta-analysis", "randomized control trial", and "systematic review"). <i>Results</i>: The literature was analyzed and 67 items relevant to the subject of this study were selected. This article points out the differences in NSE levels in different clinical groups, such as patients after an incident of hypoxic/ischemic encephalopathy (HIE), neuroinfection, or particular inflammatory processes in the nervous system region, as well as central nervous system (CNS) injury, selected MD, neurodegenerative disorders (NGDs), headaches, or epilepsy (EP). <i>Conclusions</i>: In the future, they may serve to support further work on the use of enolase as a potential biomarker of the described diseases.