Central disorders of hypersomnolence: a narrative review on current and potential biomarkers

Central disorders of hypersomnolence are currently diagnosed in clinical practice from overnight polysomnography and multiple sleep latency test (MSLT). Cerebrospinal fluid (CSF) orexin levels are also a useful confirmatory test for type 1 narcolepsy. The diagnosis and differentiation of disorders of hypersomnolence remain limited by the lack of repeatability of MSLT and the absence of any known biomarkers for type 2 narcolepsy (NT2) and idiopathic hypersomnolence (IH). There remains limited understanding of the pathophysiology and neural pathways involved in NT2 and IH. In this narrative review, we explore the research on serum and CSF testing, neuroimaging, polysomnography and other modalities in improving the sensitivity and specificity of diagnosing these disorders.