Identification of biomarkers in Lewy-body disorders.

Dementia with Lewy bodies (DLB) may account for up to 30% of all dementia cases. The symptoms of DLB can be difficult to disentangle from other dementia subtypes, particularly Alzheimer's disease (AD). AD and DLB pathologies often overlap within individuals. Like DLB, Parkinson's disease dementia (PDD) also shares common features with DLB. Currently, whether an individual is diagnosed with PDD or DLB depends solely on the timing of symptom onset. Early, accurate diagnosis is needed for optimal management and treatment. It is hoped that the development of existing and new Lewy body disorders biomarkers will facilitate more accurate diagnosis. Reduced dopamine transporter levels in DLB as shown with [123I]FP-CIT-SPECT currently appears to be the most reliable and valid biomarker, although other (predominantly imaging-based) methods also appear to have the high sensitivity and specificity required for a good biomarker. This includes (in DLB compared to AD) reduced cardiac 123I-MIBG uptake, occipital hypometabolism on FDG-PET and preservation of medial temporal lobe structures on CT/MRI. Perfusion SPECT, cerebrospinal fluid protein levels (amyloid, tau and α-synuclein), electroencephalography, saccadic eye movement tracking and 11C-PiB amyloid imaging also hold promise as biomarkers in terms of differentiating DLB, AD, PDD and other neurodegenerative disorders, although findings are less consistent. Studies utilising a combination approach in which two or more potential biomarkers are compared seem to provide very good sensitivity and specificity. In general, longitudinal studies, pathological confirmation of diagnosis and the combined approach may hold the most promise for the identification of biomarkers.