LAUSR

The clinical criteria for the diagnosis of dementia with Lewy bodies (DLB) were revised in the Fourth Consensus Report of 2017; the new criteria replaced those of the Third Report of the DLB Consortium, which was published in 2005. According to the 2005 criteria, a diagnosis of probable DLB was to be made when a patient had dementia with at least two of three core features, namely recurrent visual hallucinations, fluctuating cognition, and/or spontaneous parkinsonism. If only one core feature was present, at least one of three suggestive features—rapid eye movement (REM) sleep behaviour disorder (RBD), severe neuroleptic sensitivity, or low dopamine transporter uptake in the basal ganglia—had to be demonstrated on singlephoton emission computed tomography or positron emission tomography. In the revised criteria of 2017, RBD was upgraded to become the fourth core clinical feature. Additionally, the three suggestive features have been replaced by three indicative biomarkers: low dopamine transporter uptake, abnormal (low) uptake of Imetaiodobenzylguanidine on cardiac scintigraphy, and polysomnographic confirmation of REM sleep without atonia. If only one core clinical feature is present, diagnosis of probable DLB can be made based on the presence of at least one indicative biomarker. Neuropathological findings remain the only way to diagnose DLB definitively and are the gold standard. By comparison, the 2005 criteria have a sensitivity and specificity of 73% and 93%, respectively. To our knowledge, there have been no studies thus far comparing the diagnostic accuracy of the fourth criteria and neuropathological data. Ideally, the fourth criteria should have a higher sensitivity than the third criteria and a specificity that is equal or higher. We wanted to know if the application of the fourth set of criteria to a population of patients with a clinical diagnosis of probable DLB could identify patients who would not have been diagnosed by the third set. We reviewed all the medical files of patients from our memory clinic who had received a clinical diagnosis of probable DLB between 1 June 2010 and 31 January 2020. Diagnosis of probable DLB was based on the third or fourth consensus criteria depending on the time of diagnosis. For each patient, we noted the presence or absence of the different clinical features (i.e. recurrent visual hallucinations, cognitive fluctuation, RBD, and spontaneous parkinsonism) at the time of diagnosis, the suggestive features of the third set of criteria, and the indicative biomarkers of the fourth. This study was approved by the hospital’s ethics committee. Ninety-two patients with probable DLB were included in the study. Their demographic and clinical data are presented in Table 1. All patients fulfilled the 2017 criteria for probable DLB, whereas only 88 patients (95.6%) fulfilled the 2005 criteria. The four patients who did not fulfil the 2005 criteria were significantly younger than those who did (two-sided ttest with unequal variance, P = 0.001), and all had RBD and low dopamine transporter uptake. Our data suggest that the 2017 criteria for DLB have a higher sensitivity than the 2005 criteria because they enable the diagnosis of patients with cognitive deterioration associated with an isolated RBD and do so with the help of dopamine transporter imaging. Therefore, if a patient has a bed partner, it is crucial that that person be carefully questioned about the presence of RBD (e.g. talking during sleep, acting out dreams, and falling out of bed); this should be systematically done during each work-up for chronic cognitive disorders, as it seems more reliable than polysomnography. This might be explained by the fact that RBD, although very common in DLB patients, does not occur frequently in individual patients and may be a fluctuating symptom, occurring daily or only once a year. In the present study, two patients with RBD underwent polysomnography that did not reveal the absence of muscle atonia during REM sleep. In the near future, the use of wearable