Mild Cognitive Impairment Predicts Phenoconversion in Patients With iRBD

Mild cognitive impairment (MCI) may be considered an early sign of phenoconversion in patients with isolated rapid eye movement (REM) sleep behavior disorder (iRBD), although no wide consensus has been reached as yet, according to findings of a cross-sectional study published in the journal Sleep Medicine.

Recognizing that early detection of patients with iRBD who are at an elevated risk for phenoconversion is critical for clinicians, researchers sought to compare the differences in neuropsychiatric, neuropsychological, and neuroimaging markers of neurodegeneration in patients with MCI-iRBD and those with iRBD and normal cognition (NC).

A total of 61 participants with iRBD were enrolled in the current study — with 30 patients in the iRBD-MCI group and 31 individuals in the iRBD-NC group. A total of 78.8% of the patients were men. Individuals in both groups underwent neuropsychiatric and neuropsychological evaluations to assess psychopathologic symptoms and neuropsychological functions. Further, brain [18F]fluorodeoxyglucose positron emission tomography ([18F]FDG PET) and 1231-I-Ioflupane (FP-CIT) single-photon emission computed tomography (SPECT) were performed in all participants, in order to assess brain glucose metabolism and nigrostriatal function in convenient patient subgroups, respectively.

Comparisons between the groups demonstrated a statistically significant difference in reaction times in the Stroop Task, with considerably longer reaction times for color naming list (P <.05) and for the interference list (P <.01) in the iRBD-MCI group.

According to visuospatial memory scores, significantly lower scores on immediate reproduction (P <.01), delayed reproduction (P <.01), and immediate recall (P <.01) were observed in the iRBD-MCI group than in the iRBD-NC group, which was indicative of poor visuospatial function. Attentional-executive functions were impaired in iRBD individuals with MCI compared with patients with iRBD with NC.

Based on neuroimaging results, reduced brain glucose uptake was observed in the bilateral posterior cingulate cortex, as well as more evident nigrostriatal deafferentation in individuals in the iRBD-MCI group. The researchers did not find differences in pathologic symptoms were observed between the 2 groups.

Some limitations of the present analysis should be noted. The cross-sectional design of the study did not permit the researchers to demonstrate an increased risk for phenoconversion in patients with iRBD who were coaffected by MCI. Additionally, although the sample size was considered large for a single sleep medicine center study, the number of patients was nonetheless insufficient to use parametric analyses; thus, only preliminary observations could be made.

“The present findings highlight the presence of a diffuse neurodegenerative process affecting the entire brain of iRBD patients, possibly reflecting the higher risk of phenoconversion in iRBD-MCI than in iRBD-NC patients,” the researchers noted.

They concluded that the study findings highlight “the importance of identifying iRBD patients with MCI for urgent neuroprotective trials.”

Disclosure: None of the study authors has declared affiliations with biotech, pharmaceutical, and/or device companies.