Early diagnosis of prodromal dementia with Lewy bodies using clinical history of probable REM sleep behaviour disorder and cardiac I-MIBG scintigraphy in memory clinics.

Background: Rapid eye movement sleep behaviour disorder (RBD) is associated with reduced cardiac I-metaiodobenzylguanidine (MIBG) uptake and often precedes the onset of Lewy body (LB) disorders. We investigated the role of cardiac I-MIBG scintigraphy in relation to probable RBD for the clinical diagnosis of prodromal dementia with Lewy bodies (DLB) in memory clinics.

Methods: We reviewed clinical profiles of 60 consecutive patients who underwent cardiac I-MIBG scintigraphy in our memory clinics. The diagnostic threshold of 2.20 was used as the cut-off for the heart-to-mediastinum ratio at the delayed phase.

Results: Cardiac I-MIBG abnormality was identified in 28 patients at baseline; six were cognitively unimpaired, six had mild cognitive impairment (MCI)-LB, and 16 had probable DLB based on the National Institute on Aging and Alzheimer's Association Research Framework. Although the number of core features increased in accordance with the progression of three cognitive categories, there were no differences in the prevalence of probable RBD and the cardiac MIBG scintigraphy indices among them. During the observation period, two cognitively unimpaired patients with probable RBD progressed to MCI-LB, and three MCI-LB patients with probable RBD developed DLB. The prevalence of final diagnosis of probable MCI-LB or DLB was significantly higher in these patients (85%) than the remaining 32 patients without (9%). Of 25 patients with probable RBD, 22 (88%) had a cardiac I-MIBG abnormality regardless of cognitive conditions. Only one patient consulted a sleep centre for the abnormal sleep behaviour before visiting our memory clinics. Regarding the gender differences, male predominance was not identified and sleep-related injury more frequently occurred in men (7/12, 58%) than in women (1/10, 10%).

Conclusions: Proactive detection of probable RBD plus cardiac I-MIBG abnormality provides the opportunity for an early diagnosis of prodromal DLB in memory clinics. This approach warrants further follow-up studies with polysomnographic and pathological verification.