The age of onset is typically between the ages of 60 to 80 and males may be a greater risk. The average length of duration is around 6 years but is variable. The disease typically has a rapid, fluctuating progressive course. The key features of DLB include fluctuating cognitive impairment with episodic delirium, prominent psychiatric symptoms including visual hallucinations and some further signs such as rigidity and slowing of and difficulty initiating movements.

Other supporting features of DLB are repeated falls, syncope (fainting), and loss of consciousness. Neuroleptic sensitivity may also be an important indication of DLB. Medications such as haloperidol can lead to a severe adverse reaction which results in increase symptoms. Delusions are also supportive of the diagnosis of DLB. These usually are based on recollection of hallucinations and other perceptual disturbances. As a result, the content of the delusions may be complex and bizarre.

Diagnosis of DLB cannot achieve 100% accuracy until autopsy. Using special staining techniques the distinctive brainstem Lewy bodies and somewhat less distinctive cortical Lewy bodies can be identified with the microscope. The genetics of DLB are not clear and because approximately 75% of DLB cases share AD clinical and pathological features, it is likely to share genetic influences. The presence of the ApoE-4 allele is a risk factor for both AD and DLB. However, the presence of ApoE-4 does not distinguish DLB from AD, nor does its absence rule out either disorder.

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