Dementia Classification: Neurocognitive Disorder
Dementia is formally classified as a neurocognitive disorder—specifically termed "major neurocognitive disorder" in modern diagnostic nomenclature—and is not categorized as a primary mental illness, though psychiatric symptoms frequently co-occur and can complicate diagnosis. 1, 2
Official Diagnostic Classification
The Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) uses the term "major neurocognitive disorder" as the formal diagnostic label for what is clinically known as dementia, distinguishing it from primary psychiatric disorders 3, 4, 5. This terminology reflects the underlying neurological basis of the condition—brain disease or brain injury causing cognitive decline—rather than a primary psychiatric etiology 3.
The core distinction is that dementia represents chronic acquired impairment in cognitive domains caused by structural or functional brain pathology, whereas mental illnesses are primary psychiatric conditions without this neurodegenerative basis. 2
Diagnostic Criteria That Define It as Neurocognitive Disorder
Dementia diagnosis requires three essential elements that distinguish it from psychiatric disorders 2:
- Functional impairment: Cognitive or behavioral symptoms must interfere with ability to function at work or usual activities 1, 2
- Documented decline: Symptoms must represent decline from previous levels of functioning 1, 2
- Exclusion of primary psychiatric causes: Symptoms cannot be better explained by delirium or major psychiatric disorder 1, 2
The diagnosis requires impairment in at least two of five cognitive domains: memory, executive function, visuospatial abilities, language, or personality/behavior 1, 2. This multi-domain cognitive impairment pattern is characteristic of neurodegenerative disease rather than primary psychiatric illness 3.
The Complex Relationship with Psychiatric Disorders
A critical clinical pitfall is that psychiatric symptoms are extremely common in dementia and can be the presenting feature, but this does not make dementia a psychiatric disorder. 3
The interplay is bidirectional and complex 3:
- More than half of patients who develop dementia have depression or irritability symptoms before cognitive impairment becomes apparent 3
- Specific dementia subtypes (frontotemporal dementia, Lewy body dementia, Huntington's disease) can present with prominent psychiatric symptoms that are difficult to differentiate from primary psychiatric disorders 3
- However, patients with behavioral variant frontotemporal dementia most often do not fulfill formal DSM-5 criteria for another mental disorder when rigorously evaluated 3
The key differentiator is that emotional distress characterizing most psychiatric disorders is usually absent in dementia patients, who instead show prominent emotional blunting and lack of insight. 3
Practical Clinical Implications
When evaluating suspected dementia, you must actively exclude primary psychiatric disorders through rigorous application of DSM-5 criteria combined with expert clinical judgment 3. The presence of psychiatric symptoms does not automatically indicate a psychiatric disorder—it may represent the neuropsychiatric manifestations of underlying neurodegenerative disease 3, 6.
Consultation with a psychiatrist with expertise in frontotemporal dementia is recommended when primary psychiatric disorders are on the differential diagnosis, as this requires specialized diagnostic expertise. 3
The distinction matters clinically because treatment approaches differ fundamentally: dementia requires management of the underlying neurodegenerative process and its behavioral manifestations, whereas primary psychiatric disorders require psychiatric treatment 6, 5.