Differential Diagnosis
Normal cognition. The differential diagnosis between  normal cognition and mild NCD,
as between mild and major NCD, is challenging because the boundaries are inherently ar-
bitrary. Careful history taking and objective as sessment are critical to  these distinctions. A
longitudinal evaluation using quantified a ssessments may be key in detecting mild NCD.
Delirium. Both mild and major NCD may be difficult to distinguish from a persistent de-
lirium, which can co-occur. Careful assessment  of attention and arou sal will help to make
the distinction.
Major depressive disorder. The distinction between mild NCD and major depressive
disorder, which may co-occur with NCD, can also be challenging. Specific patterns of cog-
nitive deficits may be helpfu l. For example, consistent memory and executive function
deficits are typical of Alzheimer’s disease, whereas nonspecific or more variable perfor-
mance is seen in major depression. Alternat ively, treatment of the depressive disorder
with repeated observation over time may be required to make the diagnosis.
Specific learning disorder and other neurodevelopmental disorders. A careful clari-
fication of the individual’s baseline status will help distinguish an NCD from a specific
learning disorder or other neurodevelopmental disorders.  Additional issues may enter the
differential for specific etiological subtypes, as described in the relevant sections.
Comorbidity 
NCDs are common in older individuals and thus  often co-occur with a wide variety of age-
related diseases that may co mplicate diagnosis or treatme nt. Most notable of these is
delirium, for which NCD increases the risk. In  older individuals, a delirium during hos-