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The frequency of DLB has been estimated at 1/893 person-years. DLB is not considered a rare disease. In the overall general population, prevalence estimates vary greatly and range from 1/5,882 in Japan to 1/135 individuals in Finland. In the general population over 65 years of age, prevalence estimates are variable and range from less than 1/1,000 up to 1/ 20 individuals and from less than 1/59 up to 1/ 3 individuals with dementia (>65). Autopsy studies of elderly patients with dementia revealed that 1/4 to 1/7 had Lewy bodies.
In its early stages, DLB is not easily distinguished from Parkinson's disease (PD); it rarely resembles Alzheimer's disease (AD). At the onset of DLB, in contrast to AD, individuals often do not present with memory impairment but rather with an impairment of executive functions. Core clinical manifestations consist of 1) a fluctuating cognitive decline particularly pronounced fluctuations in attention, awareness, alertness and vigilance; 2) (visual) hallucinations; 3) PD symptoms. Symptoms such as recurring falls, transient unconsciousness, syncope, depression, systemic delusions, REM sleep behavior disorder and severe autonomic dysfunction such as urinary incontinence and orthostatic dysregulations are supportive for DLB diagnosis.
DLB usually appears sporadically (isolated). Genetic risk factors for DLB include the PARK11 gene locus and mutations in the glucocerebrosidase gene, GBA. Furthermore the ε4 allele of the apolipoprotein E gene occurs more frequently in DLB diagnosed individuals.
Diagnosis requires a careful clinical assessment based on the international consensus on clinical-diagnostic criteria and the patient's medical history. Attenuated dopaminergic reuptake in the basal ganglia in FP-CIT SPECT scanning (DAT scan) increases diagnostic certainty. Other characteristics suggestive for DLB include a lack of temporal atrophy in MRI and REM sleep behavior disorder (EEG). EEG may also show early generalized background slowing with abnormal transients in the temporal lobes or frontally dominant burst pattern. Some rare cases may reveal sympathetic denervation with a scintigraphy of the myocardium.
There can be a large clinical overlap between DLB and AD which sometimes results in the diagnosis of 'in-between' Lewy Body variant of Alzheimer's disease. If PD symptoms precede cognitive impairment by 12 months or longer, the disorder is called PDD and not DLB, but this is an arbitrary consensus among clinicians and not a disease definition. Retrospective history can be a major problem in DLB. Differential diagnosis also includes normal pressure hydrocephalus (see this term) (estimates of in 1/10 patients with dementia).
It is important to make an early diagnosis because of therapeutic implications. Although curative treatment is not yet available, cholinesterase inhibitors may substantially relieve symptoms in some cases, although large trials are lacking. Levodopa monotherapy is usually advised to alleviate PD symptoms. Atypical neuroleptics are important in managing symptoms and should be used in low dosages.
DLB is a progressive dementia disorder. Life expectancy is estimated to be about 8 years after the age of onset but may vary according to phenotype.