Diagnosis of Dementia: Essential Criteria
All of the above criteria are required for a diagnosis of dementia. The diagnosis mandates three essential elements: impairment in at least two cognitive domains, documented functional impairment, and exclusion of reversible causes 1.
Core Diagnostic Requirements
A dementia diagnosis requires the simultaneous presence of all three components 2, 3, 1:
1. Impairment of At Least Two Cognitive Domains
Cognitive impairment must involve a minimum of two of the following five domains: memory (ability to acquire and remember new information), executive function (reasoning and judgment), visuospatial abilities, language functions, or personality/behavioral changes 2, 1.
The cognitive impairment must be detected through both history-taking from a knowledgeable informant and objective cognitive assessment (bedside mental status examination or neuropsychological testing) 1.
Memory impairment is not always the primary deficit—nonamnestic presentations can occur, particularly with onset before age 65, including language-predominant, visuospatial-predominant, or executive dysfunction-predominant presentations 1.
2. Evidence of Functional Impairment
Cognitive or behavioral symptoms must interfere with the ability to function at work or usual daily activities 2, 1.
This represents the critical distinction from mild cognitive impairment (MCI), where cognitive deficits are present but do not significantly interfere with daily functioning 2, 1.
The symptoms must represent a documented decline from previous levels of functioning and performance, not lifelong cognitive limitations 2, 1.
3. Ruling Out Potential Reversible Causes
Symptoms must not be explained by delirium or major psychiatric disorder 2, 1.
Laboratory evaluation should include thyroid function tests (TSH, free T4), vitamin B12 and folate levels, and HIV testing if risk factors are present 3.
Reversible causes (neuroinfections, normal pressure hydrocephalus, vitamin B12 deficiency) account for approximately 18% of dementia presentations and can result in moderate to severe cognitive dysfunction 4.
Neuroimaging (MRI preferred over CT) is recommended to exclude structural causes such as stroke, tumor, or normal pressure hydrocephalus 2, 3.
Diagnostic Algorithm
Step 1: Obtain detailed history from both the patient and a knowledgeable informant about onset, progression pattern, and impact on instrumental activities of daily living 1.
Step 2: Perform objective cognitive assessment using standardized tools (MMSE or MoCA) to document impairment in multiple cognitive domains 3, 1.
Step 3: Assess functional impairment using validated instruments (Pfeffer FAQ, Lawton IADL Scale, or DAD) with informant input 3.
Step 4: Complete laboratory workup to exclude reversible causes (thyroid function, B12, folate, and other tests as clinically indicated) 3, 4.
Step 5: Obtain neuroimaging (MRI preferred) to identify structural abnormalities and exclude other etiologies 2, 3.
Common Pitfalls to Avoid
Relying solely on patient self-report without informant corroboration leads to missed diagnoses due to lack of insight in dementia patients 3.
Failing to use standardized, validated instruments reduces diagnostic accuracy and makes longitudinal tracking unreliable 3.
Overlooking reversible causes: Clinically suspected in only 58% of cases where they were actually present, yet most patients showed substantial improvement with treatment 4.
Assuming memory must be the primary deficit: Nonamnestic presentations are common and valid dementia presentations 1.