Increasing clinical attention has been focused on cardiac
sympathetic denervation for the differential diagnosis of
dementia with Lewy bodies (DLB) from
Alzheimer's disease (AD) with the development of [123I] metaiodobenzylguanidine (
MIBG) scintigraphy. Decreased
MIBG uptake, which reflects cardiac
sympathetic denervation, has been detected in DLB, but not in AD. However, the time course of detected cardiac sympathetic degeneration is poorly understood in DLB. Herein, the authors report two patients with a clinical diagnosis of amnestic
mild cognitive impairment (MCI) who had cardiac
sympathetic denervation, detected by cardiac (123)I-MIBG scintigraphy, without the core clinical features of DLB. One amnestic MCI patient had nocturnal dream enactment behavior, consistent with clinically probable
REM sleep behavior disorder (RBD), and converted to probable DLB with the development of recurrent
visual hallucination and spontaneous
parkinsonism two years after MCI is diagnosed. The other amnestic MCI patient exhibited occipital metabolic reduction on [18F]-fluoro-
d-glucose (FDG) positron emission tomography (PET) scan, which is the preferentially affected region in DLB patients, although she had no core or suggestive clinical features of DLB. Both patients had abnormal findings on electrocardiogram at annual health checkups despite having no cardiac-related symptoms. Detailed clinical examinations, including angiography and echocardiogram, revealed no overt etiology, supporting the idea that cardiac
sympathetic denervation is due to underlying
Lewy body disease. The clinical courses of these patients suggest that (123)I-MIBG cardiac scintigraphy is useful for the detection of DLB in the predementia phase, even before core clinical features appear.