Development

Sudden, sometimes with a definite beginning point

Slow, with an uncertain beginning point

Cause

Almost always another condition, such as an infection, dehydration, or use or stopping of certain medications

Usually a brain disorder, such as Alzheimer disease, vascular dementia, or dementia with Lewy bodies

Main early symptom

Inability to pay attention

Loss of memory, especially for recent events

Effect at night

Almost always worse

Often worse

Level of alertness (consciousness)

Impaired to varying degrees, can vary from being hyperalert to sluggish

Normal until late stages

Orientation to surroundings

Varies

Impaired

Effect on language

Slowed speech, often with incoherent and inappropriate language

Sometimes difficulty finding the right word

Memory

Varies

Lost, especially for recent events

Progression

Causes variations in mental function—people are alert one moment and sluggish and drowsy the next

Slowly progresses, gradually but eventually greatly impairing all mental functions

Duration

Days to weeks, sometimes longer

Almost always permanent

Need for treatment

Immediate

Needed but less urgently

Effect of treatment

Usually resolution of the symptoms

May slow progression but cannot reverse or cure the disorder