Cerebrospinal fluid (CSF) levels of neurofilament light protein (NFL), a marker of neuronal damage, are normal in Parkinson's disease (PD) but elevated in multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). Therefore, CSF NFL can help differentiate between PD on one hand and MSA/PSP on the other. In the present study of 10 patients with PD, 21 with MSA, 14 with PSP, 11 with corticobasal degeneration (CBD), and 59 healthy controls, this previous observation is confirmed and also extended to include CBD by showing that similarly high CSF NFL levels are seen not only in MSA and PSP but also in CBD. CSF levels of glial fibrillary acidic protein (GFAP), a protein expressed mainly in fibrillary astrocytes, were similar in all investigated groups. In addition, consecutive analyses of CSF NFL and CSF GFAP levels showed relatively stable levels over time in all the investigated parkinsonian disorders, suggesting that the rate of neuronal degeneration is rather constant over time. Our results suggest that measurements of CSF NFL but not GFAP can be useful in the differential diagnosis of PD versus atypical parkinsonian disorders (APD). However they do not help differentiate between the different APD.
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