620 Neurocognitive Disorders
agnosis” for this disorder). Disease course may be characterized by occasional plateaus
but eventually progresses through severe deme ntia to death. Average duration of survival
is 5–7 years in clinical series. Onset of symptoms is typically observed from the sixth
through the ninth decades of life, with most cases having their onset when affected indi-
viduals are in their mid-70s.
Risk and Prognostic Factors 
Genetic and physiological. Familial aggregation may occur, and several risk genes have
been identified, but in most cases of NCDLB, there is no family history.
Diagnostic Markers
The underlying neurodegenerative disease is  primarily a synucleinopathy due to alpha-
synuclein misfolding and aggregation. Cognitiv e testing beyond the use of a brief screen-
ing instrument may be necessary to define de ficits clearly. Assessment scales developed to
measure fluctuation can be useful. The associated condition REM sl eep behavior disorder
may be diagnosed through a formal sleep study or identified by questioning the patient or
informant about relevant symptoms. Neurolep tic sensitivity (challenge) is not recom-
mended as a diagnostic marker but raises suspicion of NCDLB if it occurs. A diagnosti-
cally suggestive feature is low striatal dopa mine transporter uptake on single photon
emission computed tomography  (SPECT) or positron emission tomography (PET) scan.
Other clinically useful markers potentially include relative preservation of medial tempo-
ral structures on computed tomography (C T)/magnetic resonance imaging (MRI) brain
scan; reduced striatal dopamine transporter uptake on SPECT/PET scan; generalized low
uptake on SPECT/PET perfusion scan with re duced occipital activity; abnormal (low up-