Parkinson disease (PD) is the second most common neurodegenerative disorder, affecting >1% of the population ≥65 years of age and with a prevalence set to double by 2030. In addition to the defining motor symptoms of PD, multiple non-motor symptoms occur; among them, cognitive impairment is common and can potentially occur at any disease stage. Cognitive decline is usually slow and insidious, but rapid in some cases. Recently, the focus has been on the early cognitive changes, where executive and visuospatial impairments are typical and can be accompanied by memory impairment, increasing the risk for early progression to dementia. Other risk factors for early progression to dementia include visual hallucinations, older age and biomarker changes such as cortical atrophy, as well as Alzheimer-type changes on functional imaging and in cerebrospinal fluid, and slowing and frequency variation on EEG. However, the mechanisms underlying cognitive decline in PD remain largely unclear. Cortical involvement of Lewy body and Alzheimer-type pathologies are key features, but multiple mechanisms are likely involved. Cholinesterase inhibition is the only high-level evidence-based treatment available, but other pharmacological and non-pharmacological strategies are being tested. Challenges include the identification of disease-modifying therapies as well as finding biomarkers to better predict cognitive decline and identify patients at high risk for early and rapid cognitive impairment.

ObjectiveTo determine the diagnostic relevance of myelin oligodendrocyte glycoprotein antibodies (MOG-Abs) in CSF of seronegative cases by retrospectively analyzing consecutive time-matched CSF of 80 MOG-Ab–seronegative patients with demyelinating disease.MethodsThe cohort included 44 patients with NMOSD and related disorders and 36 patients with multiple sclerosis (MS). Two independent neurologists blinded to diagnosis analyzed MOG-Abs by live cell-based immunofluorescence assay with goat anti-human immunoglobulin (Ig) G (whole molecule) antibody. Sera were tested at dilutions of 1:20 and 1:40, and a cutoff of 1:160 was considered for serum positivity. CSF specimens were tested undiluted and at 1:2 dilution with further titrations in case of positivity. Anti-IgG–Fc and anti-IgM-µ secondary antibodies were used to confirm the exclusive presence of MOG-IgG in positive cases. CSF of 13 MOG-Abs seropositive cases and 36 patients with neurodegenerative conditions was analyzed as controls.ResultsThree seronegative cases had CSF MOG-Abs (4% of the whole cohort or 7% of cases excluding patients with MS, in which MOG-Abs seem to lack diagnostic relevance). In particular, 2 patients with neuromyelitis optica spectrum disorder (NMOSD) and 1 with acute disseminated encephalomyelitis had MOG-Abs in CSF. Analysis with anti-IgG–Fc and anti-IgM confirmed the exclusive presence of MOG-IgG in the CSF of these patients. Among the control group, MOG-Abs were detectable in the CSF of 8 of 13 MOG-Ab–seropositive cases and in none of the patients with neurodegenerative disorders.ConclusionAlthough serum is the optimal specimen for MOG-Ab testing, analyzing CSF could improve diagnostic sensitivity in seronegative patients. This observation has relevant diagnostic impact and might provide novel insight into the biological mechanisms of MOG-Ab synthesis.