Which statement best defines dementia?

• A. A temporary delirium caused by infection
• B. Short-term memory loss due to dehydration
• C. Reduced mental or cognitive functioning after age 18 with various causes
• D. A childhood developmental delay

Answer: (C)

Dementia is a chronic, progressive decline in cognitive function caused by brain disease, not a normal part of aging and not a temporary issue. The statement that best defines dementia reflects this by describing reduced mental or cognitive functioning that begins after adulthood and can arise from various underlying causes, such as neurodegenerative diseases or vascular problems, leading to problems with memory, thinking, and other mental abilities over time. This helps distinguish dementia from delirium, which is an acute, often reversible state due to infection or other immediate factors; from temporary cognitive issues like dehydration; and from a childhood developmental delay, which is present from early life rather than developing later in adulthood.