Dementia
Dementia is a clinical syndrome characterised by progressive cognitive decline that interferes with independent functioning. It is an important differential diagnosis in any older adult presenting with new-onset psychotic symptoms, as paranoid delusions are common in dementing illnesses and may be mistaken for a primary psychotic disorder such as schizophrenia or delusional-disorder.
Why Does This Happen? (First Principles)
💡 FIRST PRINCIPLE: Dementia involves progressive neuronal loss and brain atrophy, most commonly due to neurodegenerative diseases such as Alzheimer’s disease. The cognitive deficits — particularly in memory, executive function, and language — arise from the specific brain regions affected. Psychotic symptoms such as paranoid delusions occur secondary to the cognitive impairment: the patient cannot accurately process and verify information about their environment, leading to misinterpretations that solidify into fixed false beliefs.
Aetiology & Risk Factors
- Alzheimer’s disease (most common cause)
- Vascular dementia
- Lewy body dementia (commonly presents with visual hallucinations)
- Frontotemporal dementia
- Parkinson’s disease dementia
Clinical Features
Cognitive Symptoms
- Progressive memory impairment (especially short-term memory).
- Deficits in executive function, language, and visuospatial skills.
- Disorientation to time, place, and person.
Psychiatric Symptoms
- Paranoid delusions are common, particularly in moderate stages.
- Visual hallucinations are characteristic of Lewy body dementia.
- Agitation, aggression, and sleep disturbance may occur.
Key Distinguishing Features from Delusional Disorder
- Significant cognitive impairment on cognitive testing (e.g., Mini-Mental State Examination [MMSE]).
- Progressive course — dementia worsens over time, unlike delusional disorder where cognition remains intact.
- Multiple cognitive domains affected — not just memory but also language, executive function, and visuospatial ability.
⚠️ EXAM DETAIL: In elderly patients presenting with new-onset paranoid delusions, dementia must be assessed with cognitive testing, as delusional disorder and schizophrenia also occur in this age group but have different management and prognosis.
Investigations
- Cognitive assessment (MMSE, Montreal Cognitive Assessment [MoCA]).
- Neuroimaging to identify structural causes.
- Blood work to exclude reversible causes (vitamin B12, thyroid function, syphilis serology).
Management
📝 TODO: Needs source — pharmacological (acetylcholinesterase inhibitors, memantine) and non-pharmacological management of dementia; management of psychotic symptoms in dementia.
Differential Diagnosis
| Condition | Distinguishing Features |
|---|---|
| delusional-disorder | Cognitive function intact, no progressive decline, personality preserved (outside the delusion). |
| schizophrenia | Onset typically in early adulthood, chronic course with negative symptoms, no progressive cognitive decline of the dementia type. |
| delirium | Acute onset, fluctuating consciousness, attention deficits, identifiable medical trigger. |
| depression (pseudodementia) | Cognitive complaints that improve with depression treatment; no progressive decline. |
Exam Focus
Viva Questions
- How do you differentiate dementia from delusional disorder in an elderly patient with paranoid delusions? (Cognitive testing reveals significant impairment in dementia; personality and function are preserved in delusional disorder.)
- What type of hallucinations are characteristic of Lewy body dementia? (Well-formed visual hallucinations.)
OSCE Scenarios
- Cognitive assessment of an elderly patient with new-onset paranoid ideation — performing and interpreting an MMSE.
MCQ Traps
- ⚠️ EXAM DETAIL: New-onset psychosis in an elderly patient should always prompt cognitive testing to exclude dementia.
- ⚠️ EXAM DETAIL: Visual hallucinations are more characteristic of Lewy body dementia than Alzheimer’s disease.
Source Notes
- Information in this page is drawn from the differential diagnosis discussion in delusional-disorder, which is sourced from the Handbook of Clinical Psychiatry (de Silva & Hanwella) and Dr. Ajith Jayasekara’s lectures.